Whether you're just getting ideas for your Cisco home lab or adding to your existing lab, ebay is a great place to get ideas for your lab as well as pick up some great bargains.
Of course, the internet being what it is, there are always going to be a few people looking to take your money while shipping you inferior merchandise, or worse, no merchandise at all. While these "dealers" are in the minority, you still need to be careful when purchasing Cisco equipment on ebay. In this article, I'll give you several tips on browsing ebay ads for home lab ideas, and a few things to look out for when purchasing equipment on ebay.
For those of you just starting your Cisco certification pursuit, the idea of purchasing a home lab kit -- a set of routers, switches, and perhaps some cables and study guides -- seems like a good idea. Instead of putting your lab together one piece at a time, these kits allow you to get a head start on your studies.
One thing to watch out for in these kits is outdated equipment, or the inclusion of outdated study guides. Often, vendors will use these kits as a way to get rid of unwanted inventory.
The Cisco 1900 family of switches falls into this category. A recent search on ebay for "ccna lab" showed seven different CCNA lab kits that contained 1900 switches. The problem here is that the current CCNA exams do not test on the 1900 switches, which are menu-driven and do not have an IOS. You'll need to be well-versed with switches that do have an IOS, such as the 2950s.
The plus side here is that you will probably save money by using 1900 switches. If you're on a tight budget, having a 1900 switch is better than no switch at all. If at all possible, though, get a Cisco switch with an IOS.
The cables and transceivers included with these kits are generally exactly what you need to set up that particular kit, and this can be very helpful to those CCNA candidates who are new to the various cables needed to physically configure a home lab. Just make sure you're not buying a kit with 10 transceivers (used on AUI ports) when you've only got two routers with Ethernet ports.
Watch out for kits that include outdated study guides. I've seen four-year-old CCNA books included with some kits. If you already have your study guides, feel free to ask the vendor how much the kit costs without the books.
That leads me to the most important point. Get to know the vendor before buying anything. Visit their website and check their ebay feedback. If buying from an individual as opposed to a reseller, find out what conditions the router or switch has been kept in, and make sure to define the terms under which they will accept returns.
There's nothing wrong with buying equipment from someone who's selling their CCNA/CCNP/CCIE home lab, but just make sure you ask the right questions first. Professional resellers generally have their return policy right in their ebay ad; if they don't, ask for a copy.
Building your own CCNA and/or CCNP home lab is a little intimidating at first, but speaking as someone who has climbed the Cisco certification ladder from the CCNA to the CCIE, I can tell you that it is the best investment you can make in your career. Use a little caution, ask the right question, and soon you'll be leaving the world of "router simulators" behind - and you'll be developing your skills as a true professional should: On real Cisco routers and switches!
Showing posts with label frame. Show all posts
Showing posts with label frame. Show all posts
Friday, December 26, 2008
Computer Certification: Become A Utility Player
In baseball, a "utility player" is one who plays more than one position. These players are usually backups, but they have a job in the major leagues because of their value to the team; since they can play more than one position, they have that much more value to their employer.
Too often in IT, workers become either LAN or WAN engineers, knowing little if anything about the other side. Many LAN administrators I worked with knew little about routing and switching, while many WAN engineers I knew not only didn't know much about the LAN side of their network, but they didn't want to know anything about the servers!
In today's IT world, it's a bad idea to specialize in only one thing and not know how to do anything else. Not only does it limit your future career prospects, but it limits your current prospects as well. Employers don't want to hire someone and have them get up to speed on the job - they want someone who can walk right in and do the job. The more you know, the better your chance of getting a better job - or quickly being able to get another job if you were laid off tomorrow.
A term often heard on Wall Street is "diversification", meaning that investors should not invest heavily or totally in only one stock; if that stock plummets, they're in big trouble. Your career is the most important stock you will ever own, and you're 100% in charge of it. Diversify. If you're working primarily with servers, learn some routing and switching. If you know the routing protocols your company uses on its WAN, learn something about that protocol. (If you don't know the protocol, ask!)
While you’re adding these skills, get certified while you’re at it! Adding a CCNA, MCSE, or other computer certification looks great on your resume while signaling to employers that you’re constantly adding to your skills.
Adding more skills and knowledge to your IT skill set is always a good idea. Don't limit yourself to the technologies you work with every day. Make an investment in yourself and become a well-rounded network engineer. This will help you keep the job you have - and open doors in the future that might otherwise have remained closed.
Too often in IT, workers become either LAN or WAN engineers, knowing little if anything about the other side. Many LAN administrators I worked with knew little about routing and switching, while many WAN engineers I knew not only didn't know much about the LAN side of their network, but they didn't want to know anything about the servers!
In today's IT world, it's a bad idea to specialize in only one thing and not know how to do anything else. Not only does it limit your future career prospects, but it limits your current prospects as well. Employers don't want to hire someone and have them get up to speed on the job - they want someone who can walk right in and do the job. The more you know, the better your chance of getting a better job - or quickly being able to get another job if you were laid off tomorrow.
A term often heard on Wall Street is "diversification", meaning that investors should not invest heavily or totally in only one stock; if that stock plummets, they're in big trouble. Your career is the most important stock you will ever own, and you're 100% in charge of it. Diversify. If you're working primarily with servers, learn some routing and switching. If you know the routing protocols your company uses on its WAN, learn something about that protocol. (If you don't know the protocol, ask!)
While you’re adding these skills, get certified while you’re at it! Adding a CCNA, MCSE, or other computer certification looks great on your resume while signaling to employers that you’re constantly adding to your skills.
Adding more skills and knowledge to your IT skill set is always a good idea. Don't limit yourself to the technologies you work with every day. Make an investment in yourself and become a well-rounded network engineer. This will help you keep the job you have - and open doors in the future that might otherwise have remained closed.
Cisco Certification: The "Secret" Key To Getting Your CCNA And CCNP
Whether you're working on your CCNA or CCNP, Cisco certification exams are the most demanding computer certification exams in the IT field. Cisco exams are not a test of memorization, they're a test of your analytical skills. You'll need to look at configurations and console output and analyze them to identify problems and answer detailed questions. To pass these demanding exams, you've got to truly understand how Cisco routers and switches operate - and the key to doing so is right in front of you.
The debug command.
Of course, there is no single "debug" command. Using IOS Help, you can quickly see that there are hundreds of these debugs, and I want to mention immediately that you should never practice these commands on a production router. This is one major reason you need to get some hands-on experience with Cisco products in a home lab or rack rental. No software program or "simulator" is going to give you the debug practice you need.
Now, why am I so insistent that you use debugs? Because that's how you actually see what's going on. It's not enough to type a frame relay LMI command, you have to be able to see the LMIs being exchanged with "debug frame lmi". You don't want to just type a few network numbers in after enabling RIP, you want to see the routes being advertised along with their metrics with "debug ip rip". The list goes on and on.
By using debugs as part of your CCNA and CCNP studies, you're going beyond just memorizing commands and thinking you understand everything that's happening when you enter a command or two. You move to a higher level of understanding how routers, switches, and protocols work -- and that is the true goal of earning your CCNA and CCNP.
The debug command.
Of course, there is no single "debug" command. Using IOS Help, you can quickly see that there are hundreds of these debugs, and I want to mention immediately that you should never practice these commands on a production router. This is one major reason you need to get some hands-on experience with Cisco products in a home lab or rack rental. No software program or "simulator" is going to give you the debug practice you need.
Now, why am I so insistent that you use debugs? Because that's how you actually see what's going on. It's not enough to type a frame relay LMI command, you have to be able to see the LMIs being exchanged with "debug frame lmi". You don't want to just type a few network numbers in after enabling RIP, you want to see the routes being advertised along with their metrics with "debug ip rip". The list goes on and on.
By using debugs as part of your CCNA and CCNP studies, you're going beyond just memorizing commands and thinking you understand everything that's happening when you enter a command or two. You move to a higher level of understanding how routers, switches, and protocols work -- and that is the true goal of earning your CCNA and CCNP.
Wednesday, December 24, 2008
Cisco CCNA Certification Exam Tutorial: OSPF Hub-And-Spoke
CCNA certification demands that you master the basics of OSPF, and for many studying for the CCNA exam, their first exposure to OSPF is a hub-and-spoke configuration. That's a tough way to get started, because a hub-and-spoke configuration built over an NBMA technology such as Frame Relay requires quite a bit of attention to detail. Let's take a quick look at several common OSPF configuration errors and how to avoid them on your CCNA test.
Make sure the hub is the designated router and that there are no backup designated routers. This is done by setting the OSPF interface priority to zero on the spoke routers. This not only ensures that the hub wins the DR election with its default OSPF interface priority of 1, but it prevents the spokes from ever having a chance to become the DR or BDR.
Configure neighbor statements on the hub. Since we're dealing with an NBMA network, the hub cannot dynamically discover its neighbors. Neighbor statements are not needed on the spokes. (They don't hurt anything, but they don't do anything, either.)
Finally, if your OSPF adjacencies do not form as expected, make sure to use your OSI model knowledge to approach the problem. The issue may actually be at Layer Two, with your Frame Relay configuration. If you don't use the "broadcast" option on your frame relay statements, OSPF hellos will not be transmitted successfully between potential neighbors. OSPF hellos are multicast, but the "broadcast" option for Frame Relay includes multicasts.
By paying special attention to these details, you're that much close to CCNA exam day success and earning your certification. I recommend that you get some experience with configuring OSPF hub-and-spoke before taking the CCNA exam, because it’s by actually performing tasks such as this that makes you supremely confident on CCNA test day.
Make sure the hub is the designated router and that there are no backup designated routers. This is done by setting the OSPF interface priority to zero on the spoke routers. This not only ensures that the hub wins the DR election with its default OSPF interface priority of 1, but it prevents the spokes from ever having a chance to become the DR or BDR.
Configure neighbor statements on the hub. Since we're dealing with an NBMA network, the hub cannot dynamically discover its neighbors. Neighbor statements are not needed on the spokes. (They don't hurt anything, but they don't do anything, either.)
Finally, if your OSPF adjacencies do not form as expected, make sure to use your OSI model knowledge to approach the problem. The issue may actually be at Layer Two, with your Frame Relay configuration. If you don't use the "broadcast" option on your frame relay statements, OSPF hellos will not be transmitted successfully between potential neighbors. OSPF hellos are multicast, but the "broadcast" option for Frame Relay includes multicasts.
By paying special attention to these details, you're that much close to CCNA exam day success and earning your certification. I recommend that you get some experience with configuring OSPF hub-and-spoke before taking the CCNA exam, because it’s by actually performing tasks such as this that makes you supremely confident on CCNA test day.
Cisco CCNA Certification Exam Tutorial: Frame Relay DLCIs And Mappings
Passing the CCNA is tough, and one of the toughest parts is keeping all the acronyms straight! Frame Relay has plenty of those, and today we're going to examine what DLCIs do and how they're mapped on a Cisco router.
Frame Relay VCs use Data-Link Connection Identifiers (DLCI - pronounced "del-see") as their addresses. Unlike other Cisco technologies, VCs have only a single DLCI in their header. They do not have a source and destination.
DLCIs have local significance only. DLCI numbers are not advertised to other routers, and other routers can use the same DLCI numbers without causing connectivity issues.
Cisco uses the term global addressing to describe a technique by which a router in a frame relay network is reached via the same DLCI number from each router in the network. For example, in a 25-router network, the same DLCI number would be used to reach “Router A” by each router.
Global Addressing is an organizational tool that does not affect the fact that DLCIs have local significance only.
The locally significant DLCI must be mapped to the destination router’s IP address. There are two options for this, Inverse ARP and static mapping.
In both of the following examples, the single physical Serial interface on Router 1 is configured with two logical connections through the frame relay cloud, one to Router 2 and one to Router 3.
Inverse ARP runs by default once Frame Relay is enabled, and starts working as soon as you open the interface. By running show frame-relay map after enabling Frame Relay, two dynamic mappings are shown on this router. If a dynamic mapping is shown, Inverse ARP performed it.
R1#show frame map
Serial0 (up): ip 200.1.1.2 dlci 122(0x7A,0x1CA0), dynamic,
broadcast,, status defined, active
Serial0 (up): ip 200.1.1.3 dlci 123(0x7B,0x1CB0), dynamic,
broadcast,, status defined, active
Static mappings require the use of a frame map statement. To use static mappings, turn Inverse ARP off with the no frame-relay inverse-arp statement, and configure a frame map statement for each remote destination that maps the local DLCI to the remote IP address. Frame Relay requires the broadcast keyword to send broadcasts to the remote device.
R1#conf t
R1(config)#interface serial0
R1(config-if)#no frame-relay inverse-arp
R1(config-if)#frame map ip 200.1.1.2 122 broadcast
R1(config-if)#frame map ip 200.1.1.3 123 broadcast
The syntax of the frame map statement maps the remote IP address to the local DLCI.
Broadcasts will not be transmitted by default; the broadcast option must be configured.
R1#show frame map
Serial0 (up): ip 200.1.1.2 dlci 122(0x7A,0x1CA0), static,
broadcast,
CISCO, status defined, active
Serial0 (up): ip 200.1.1.3 dlci 123(0x7B,0x1CB0), static,
broadcast,
CISCO, status defined, active
Hands-on practice is the best way to prepare for CCNA exam success. Working with Frame Relay in a lab environment practically guarantees that you'll truly master the concepts shown here - and then you're on your way to the CCNA and becoming a master network engineer.
Frame Relay VCs use Data-Link Connection Identifiers (DLCI - pronounced "del-see") as their addresses. Unlike other Cisco technologies, VCs have only a single DLCI in their header. They do not have a source and destination.
DLCIs have local significance only. DLCI numbers are not advertised to other routers, and other routers can use the same DLCI numbers without causing connectivity issues.
Cisco uses the term global addressing to describe a technique by which a router in a frame relay network is reached via the same DLCI number from each router in the network. For example, in a 25-router network, the same DLCI number would be used to reach “Router A” by each router.
Global Addressing is an organizational tool that does not affect the fact that DLCIs have local significance only.
The locally significant DLCI must be mapped to the destination router’s IP address. There are two options for this, Inverse ARP and static mapping.
In both of the following examples, the single physical Serial interface on Router 1 is configured with two logical connections through the frame relay cloud, one to Router 2 and one to Router 3.
Inverse ARP runs by default once Frame Relay is enabled, and starts working as soon as you open the interface. By running show frame-relay map after enabling Frame Relay, two dynamic mappings are shown on this router. If a dynamic mapping is shown, Inverse ARP performed it.
R1#show frame map
Serial0 (up): ip 200.1.1.2 dlci 122(0x7A,0x1CA0), dynamic,
broadcast,, status defined, active
Serial0 (up): ip 200.1.1.3 dlci 123(0x7B,0x1CB0), dynamic,
broadcast,, status defined, active
Static mappings require the use of a frame map statement. To use static mappings, turn Inverse ARP off with the no frame-relay inverse-arp statement, and configure a frame map statement for each remote destination that maps the local DLCI to the remote IP address. Frame Relay requires the broadcast keyword to send broadcasts to the remote device.
R1#conf t
R1(config)#interface serial0
R1(config-if)#no frame-relay inverse-arp
R1(config-if)#frame map ip 200.1.1.2 122 broadcast
R1(config-if)#frame map ip 200.1.1.3 123 broadcast
The syntax of the frame map statement maps the remote IP address to the local DLCI.
Broadcasts will not be transmitted by default; the broadcast option must be configured.
R1#show frame map
Serial0 (up): ip 200.1.1.2 dlci 122(0x7A,0x1CA0), static,
broadcast,
CISCO, status defined, active
Serial0 (up): ip 200.1.1.3 dlci 123(0x7B,0x1CB0), static,
broadcast,
CISCO, status defined, active
Hands-on practice is the best way to prepare for CCNA exam success. Working with Frame Relay in a lab environment practically guarantees that you'll truly master the concepts shown here - and then you're on your way to the CCNA and becoming a master network engineer.
Cisco CCNA Certification Exam: Five Frame Relay Details You Must Know
When you're studying for your CCNA exam on the way to earning this coveted Cisco certification, the details can seem overwhelming! In this article, I'll point out five Frame Relay details that you must keep in mind when you're on your way to the CCNA exam!
Inverse ARP starts working as soon as you open the serial interface. This protocol performs dynamic Frame Relay mapping, but you don't have to enable it - it's already enabled as soon as you enter the command "encapsulation frame-relay".
When you're configuring Frame Relay map statements manually, remember that you're mapping the local DLCI to the remote IP address.
When you run "show frame map", the word "dynamic" indicates mappings created by Inverse ARP, and "static" indicates it was manually created.
To spot possible LMI type mismatches, run "show frame lmi". A large number of Status Timeouts indicates that there may be an LMI problem between your router and the frame relay switch.
This last one is for the many of you building CCNA home labs. A frame relay switch is a great addition to your lab! While you're busy putting the configuration together, don't forget the global command "frame-relay switching" - it's this command that allows a Cisco router to act as a frame relay switch!
Inverse ARP starts working as soon as you open the serial interface. This protocol performs dynamic Frame Relay mapping, but you don't have to enable it - it's already enabled as soon as you enter the command "encapsulation frame-relay".
When you're configuring Frame Relay map statements manually, remember that you're mapping the local DLCI to the remote IP address.
When you run "show frame map", the word "dynamic" indicates mappings created by Inverse ARP, and "static" indicates it was manually created.
To spot possible LMI type mismatches, run "show frame lmi". A large number of Status Timeouts indicates that there may be an LMI problem between your router and the frame relay switch.
This last one is for the many of you building CCNA home labs. A frame relay switch is a great addition to your lab! While you're busy putting the configuration together, don't forget the global command "frame-relay switching" - it's this command that allows a Cisco router to act as a frame relay switch!
Cisco CCNA Certification: The (Many) Different Kinds Of Switching
When you're studying for your CCNA exam, whether you're taking the Intro-ICND path or the single-exam path, you're quickly introduced to the fact that switching occurs at Layer 2 of the OSI model. No problem there, but then other terms involving switching are thrown in, and some of them can be more than a little confusing. What is "cell switching"? What is "circuit switching"? Most confusing of all, how can you have "packet switching"? Packets are found at Layer 3, but switching occurs at Layer 2. How can packets be switched?
Relax! As you'll see in this article, the terms aren't that hard to keep straight. Packet switching, for example, describes a protocol that divides a message into packets before they're sent. The packets are then sent individually, and may take different paths to the same destination. Once the packets arrive at the final destination, they are reassembled.
Frame switching follows the same process, but at a different layer of the OSI model. When the protocol runs at Layer 2 rather than Layer 3, the process is referred to as frame switching.
Cell switching also does much the same thing, but as the name implies, the device in use is a cell switch. Cell-switched packets are fixed in length. ATM is a popular cell-switching technology.
The process of circuit switching is just a bit different, in that the process of setting up the circuit itself is part of the process. The channel is set up between two parties, data is transmitted, and the channel is then torn down. The circuit-switching technology most familiar to CCNA candidates is ISDN.
Don't let these terms confuse you. The four different terms are describing much the same process. The main difference is that they are occurring at different levels of the OSI model, and using a different transport method to get the data where it needs to go.
Relax! As you'll see in this article, the terms aren't that hard to keep straight. Packet switching, for example, describes a protocol that divides a message into packets before they're sent. The packets are then sent individually, and may take different paths to the same destination. Once the packets arrive at the final destination, they are reassembled.
Frame switching follows the same process, but at a different layer of the OSI model. When the protocol runs at Layer 2 rather than Layer 3, the process is referred to as frame switching.
Cell switching also does much the same thing, but as the name implies, the device in use is a cell switch. Cell-switched packets are fixed in length. ATM is a popular cell-switching technology.
The process of circuit switching is just a bit different, in that the process of setting up the circuit itself is part of the process. The channel is set up between two parties, data is transmitted, and the channel is then torn down. The circuit-switching technology most familiar to CCNA candidates is ISDN.
Don't let these terms confuse you. The four different terms are describing much the same process. The main difference is that they are occurring at different levels of the OSI model, and using a different transport method to get the data where it needs to go.
Cisco CCNA Certification: Error Detection vs. Error Recovery
Passing the CCNA, Intro, and ICND exam is all about knowing and noticing the details. (Which makes perfect sense, since becoming a master networking administrator or engineer is also about noticing the details!) One such detail knows the difference between error detection and error recovery. While the terms are sometimes used interchangeably, they are not the same thing.
Error detection is just that - error detection only. Two common error detection methods are found at the Data Link layer of the OSI model, the FCS (Frame Check Sequence) and CRC (Cyclical Redundancy Check). A mathematical equation is run against the data in the frame, and the result is sent along with the data. The receiver runs the equation again, but this time. If the result is the same, the frame is considered valid; if the result is different, the frame is considered corrupt and is discarded.
Note that the FCS and CRC do nothing in regards to retransmission. They are strictly error detection schemes.
For an example of error recovery, we look to the Transport layer, where TCP runs. TCP performs reliable delivery, and the reason we call it "reliable" is that TCP uses sequence numbers to detect missing segments. If the sender determines from the sequence numbers that the remote host did not receive transmitted segments, the sender will retransmit the missing segments.
The key to keeping the terms straight in your head is to remember that while both error detection and error recovery both detect problems, only error recovery does anything about it. It's also worth reading an exam question twice when you see either term!
Error detection is just that - error detection only. Two common error detection methods are found at the Data Link layer of the OSI model, the FCS (Frame Check Sequence) and CRC (Cyclical Redundancy Check). A mathematical equation is run against the data in the frame, and the result is sent along with the data. The receiver runs the equation again, but this time. If the result is the same, the frame is considered valid; if the result is different, the frame is considered corrupt and is discarded.
Note that the FCS and CRC do nothing in regards to retransmission. They are strictly error detection schemes.
For an example of error recovery, we look to the Transport layer, where TCP runs. TCP performs reliable delivery, and the reason we call it "reliable" is that TCP uses sequence numbers to detect missing segments. If the sender determines from the sequence numbers that the remote host did not receive transmitted segments, the sender will retransmit the missing segments.
The key to keeping the terms straight in your head is to remember that while both error detection and error recovery both detect problems, only error recovery does anything about it. It's also worth reading an exam question twice when you see either term!
Cisco CCNA / CCNP Tutorial: Home Lab Assembly Case Study
Part of your CCNA / CCNP education is deciding what network topology to use when you're putting together your home lab. Some of you are starting with one or two routers or switches, while others are starting with more. A customer recently sent me a list of his Cisco routers and switches that he has available for a home lab and asked for my help in coming up with the best way to use them.
There is no "right" or "wrong" answer to this question; again, part of the learning process is configuring and reconfiguring the physical topology of your lab. Let's look at the routers and switches he has available, including the interfaces on each, and come up with one possible CCNA / CCNP home lab setup.
The equipment list:
Two 3620 routers. Each has 1 serial port and 2 ethernet ports.
One 3640 router. This has two ethernet cards, each with two ports, and two AUI ports.
Three 2503s, my personal favorite for home labs! These have 1 AUI port, 2 serial interfaces, and one BRI interface apiece.
One 2524 router. This has one serial port, 1 ethernet port, and one BRI interface.
One 4500 router. This has eight BRI ports, 2 ethernet ports, and more importantly, four serial ports.
He also has a 5200 access server, an ISDN simulator, one 2924 switch, and one 1924 switch.
Now, if you don't have this much equipment to work with, don't panic! Most CCNA / CCNP candidates don't; this is more of an exercise in looking at what you do have and using it to the utmost.
As I've mentioned in many of my CCNA / CCNP home lab articles, an access server is a great thing to have. All he needs is an octal cable to connect his AS to the other devices we choose to use, and he's all set. (If you need an access server sample configuration, there is one on my website in the Home Lab section.)
A frame relay switch is also great to have, and the 4500 will make a great FR switch. Having a frame relay cloud in your CCNA / CCNP home lab is a great way to get experience configuring and troubleshooting frame relay, an essential skill for CCNA success.
I would put both of the 3620s on the frame relay cloud via the Serial interface, as well as two of the 2503s. That gives you four routers that will be using frame relay to communicate, and that's the most we can have since the 4500 has four serial ports. The 4500 will need to be configured as a frame relay switch and connected to the other routers via a DTE/DCE cable. (Again, if you need a frame relay switch configuration, the one I use in my pods is on the website in the same place as the access server configuration.)
The two 2503s that are on the frame relay cloud should also be connected via their BRI interfaces. The home lab also includes an ISDN simulator, which is necessary to allow routers to communicate via their BRI interfaces. Just get a couple of straight-through cables to connect those two routers to the ISDN simulator and that segment is ready to go. (Remember that you can't connect Cisco routers directly via their BRI interfaces.)
All of the routers in this lab have at least one ethernet or AUI port, so we can connect them all to either one of the switches. The switches should be connected via at least two crossover cables to allow practice with trunking, root bridge election, and VLANs. Having two switches really does add quite a bit to a CCNA / CCNP home lab's capabilities. You can experiment with different subnets and vlans with as well. Don't be afraid to dive in - that's what a home lab is all about!
So now we've got four routers connected via frame relay, two via ISDN, and the others via ethernet segments. Two of the routers that are not using their serial interfaces should be connected directly via their serial ports. For this, you'll just need another DTE/DCE cable. Knowing how to bring up the line between two directly connected serial ports is an important CCNA skill, and so is troubleshooting it. You should be able to bring such a connection up with your eyes closed, and once you work with your own CCNA / CCNP home lab, you'll be able to!
Also, don't forget to add a loopback interface to each one of your routers. I like to use 1.1.1.1 for R1, 2.2.2.2 for R2, and so on. Advertising loopbacks is another great way to get practice with RIP, OSPF, EIGRP, IGRP, and static routing.
We've taken a pile of routers and switches and turned them into a fantastic CCNA / CCNP home lab. Whether you're working with two Cisco devices or ten, coming up with your own home lab topology is a great learning experience and the beginning of developing your analytical and troubleshooting skills.
There is no "right" or "wrong" answer to this question; again, part of the learning process is configuring and reconfiguring the physical topology of your lab. Let's look at the routers and switches he has available, including the interfaces on each, and come up with one possible CCNA / CCNP home lab setup.
The equipment list:
Two 3620 routers. Each has 1 serial port and 2 ethernet ports.
One 3640 router. This has two ethernet cards, each with two ports, and two AUI ports.
Three 2503s, my personal favorite for home labs! These have 1 AUI port, 2 serial interfaces, and one BRI interface apiece.
One 2524 router. This has one serial port, 1 ethernet port, and one BRI interface.
One 4500 router. This has eight BRI ports, 2 ethernet ports, and more importantly, four serial ports.
He also has a 5200 access server, an ISDN simulator, one 2924 switch, and one 1924 switch.
Now, if you don't have this much equipment to work with, don't panic! Most CCNA / CCNP candidates don't; this is more of an exercise in looking at what you do have and using it to the utmost.
As I've mentioned in many of my CCNA / CCNP home lab articles, an access server is a great thing to have. All he needs is an octal cable to connect his AS to the other devices we choose to use, and he's all set. (If you need an access server sample configuration, there is one on my website in the Home Lab section.)
A frame relay switch is also great to have, and the 4500 will make a great FR switch. Having a frame relay cloud in your CCNA / CCNP home lab is a great way to get experience configuring and troubleshooting frame relay, an essential skill for CCNA success.
I would put both of the 3620s on the frame relay cloud via the Serial interface, as well as two of the 2503s. That gives you four routers that will be using frame relay to communicate, and that's the most we can have since the 4500 has four serial ports. The 4500 will need to be configured as a frame relay switch and connected to the other routers via a DTE/DCE cable. (Again, if you need a frame relay switch configuration, the one I use in my pods is on the website in the same place as the access server configuration.)
The two 2503s that are on the frame relay cloud should also be connected via their BRI interfaces. The home lab also includes an ISDN simulator, which is necessary to allow routers to communicate via their BRI interfaces. Just get a couple of straight-through cables to connect those two routers to the ISDN simulator and that segment is ready to go. (Remember that you can't connect Cisco routers directly via their BRI interfaces.)
All of the routers in this lab have at least one ethernet or AUI port, so we can connect them all to either one of the switches. The switches should be connected via at least two crossover cables to allow practice with trunking, root bridge election, and VLANs. Having two switches really does add quite a bit to a CCNA / CCNP home lab's capabilities. You can experiment with different subnets and vlans with as well. Don't be afraid to dive in - that's what a home lab is all about!
So now we've got four routers connected via frame relay, two via ISDN, and the others via ethernet segments. Two of the routers that are not using their serial interfaces should be connected directly via their serial ports. For this, you'll just need another DTE/DCE cable. Knowing how to bring up the line between two directly connected serial ports is an important CCNA skill, and so is troubleshooting it. You should be able to bring such a connection up with your eyes closed, and once you work with your own CCNA / CCNP home lab, you'll be able to!
Also, don't forget to add a loopback interface to each one of your routers. I like to use 1.1.1.1 for R1, 2.2.2.2 for R2, and so on. Advertising loopbacks is another great way to get practice with RIP, OSPF, EIGRP, IGRP, and static routing.
We've taken a pile of routers and switches and turned them into a fantastic CCNA / CCNP home lab. Whether you're working with two Cisco devices or ten, coming up with your own home lab topology is a great learning experience and the beginning of developing your analytical and troubleshooting skills.
Cisco CCNA / CCNP Home Labs: Developing Troubleshooting Skills
CCNA / CCNP candidates are going to be drilled by Cisco when it comes to troubleshooting questions. You're going to have to be able to analyze configurations to see what the problem is (and if there is a problem in the first place), determine the meaning of different debug outputs, and show the ability not just to configure a router or switch, but troubleshoot one.
That's just as it should be, because CCNAs and CCNPs will find themselves doing a lot of troubleshooting in their careers. Troubleshooting isn't something that can just be learned from a book; you've got to have some experience working with routers and switches. The only real way to learn how to troubleshoot is to develop that ability while working on live equipment.
Of course, your company or client is going to take a very dim view of you developing this skill on their live network. So what can you do?
Assemble a Cisco home lab. When you start working with real Cisco equipment, you're doing yourself a lot of favors. First, you're going to be amazed at how well you retain information that will become second nature to you before exam day. But more importantly, both for the exam room and your career, you're developing invaluable troubleshooting skills.
Don't get me wrong, I'm not saying knowing the theory of how routers and switches work is unimportant. Quite the opposite - if you don't know networking theory, you're not going to become a CCNA or CCNP. But the ability to apply that knowledge is vital - and the only way you can get that is to work on real Cisco routers and switches. As for these "router simulators" on the market today, ask yourself this simple question: "When I walk into a server room, how many router simulators do I see?"
I often tell students that they'll do their best learning when they screw something up. I've had many a student tell me later that I was right - when they misconfigured frame relay, ISDN, or another CCNA / CCNP technology and then had to fix it themselves, it not only gave them the opportunity to apply their knowledge, but it gave them the confidence to know they could do it.
And you can't put a price on confidence - in the exam room or in the network center!
That's just as it should be, because CCNAs and CCNPs will find themselves doing a lot of troubleshooting in their careers. Troubleshooting isn't something that can just be learned from a book; you've got to have some experience working with routers and switches. The only real way to learn how to troubleshoot is to develop that ability while working on live equipment.
Of course, your company or client is going to take a very dim view of you developing this skill on their live network. So what can you do?
Assemble a Cisco home lab. When you start working with real Cisco equipment, you're doing yourself a lot of favors. First, you're going to be amazed at how well you retain information that will become second nature to you before exam day. But more importantly, both for the exam room and your career, you're developing invaluable troubleshooting skills.
Don't get me wrong, I'm not saying knowing the theory of how routers and switches work is unimportant. Quite the opposite - if you don't know networking theory, you're not going to become a CCNA or CCNP. But the ability to apply that knowledge is vital - and the only way you can get that is to work on real Cisco routers and switches. As for these "router simulators" on the market today, ask yourself this simple question: "When I walk into a server room, how many router simulators do I see?"
I often tell students that they'll do their best learning when they screw something up. I've had many a student tell me later that I was right - when they misconfigured frame relay, ISDN, or another CCNA / CCNP technology and then had to fix it themselves, it not only gave them the opportunity to apply their knowledge, but it gave them the confidence to know they could do it.
And you can't put a price on confidence - in the exam room or in the network center!
Cisco CCNA / CCNP Home Lab Tutorial: Using 2520 Routers
I know from experience that part of the excitement and anxiety of putting together your own CCNA / CCNP home lab is deciding what to buy! While you can make a workable home lab out of almost any combination of Cisco routers and switches, some routers are better suited for home lab work than others because they can fill multiple roles.
My personal favorite is the Cisco 2520. This router has four serial interfaces, making it an ideal frame relay switch. Don't forget that just because you're using a router as a frame switch, you can still use its routing capabilities. One setup I use is to use three of the four serial interfaces for frame switching and the fourth interface as a point-to-point network with another router. All you need is some DTE/DCE cables and you're all set.
The 2520 also comes with one ethernet interface and an ISDN interface, so that gives you even more options. Even if you're not planning to run ISDN in your home lab right now, you may choose to do so in the future - and with a 2520, you've already got the right router to do so. Keep in mind that if you are going to run ISDN in your home lab, you’ll need an ISDN device such as an ISDN simulator in your lab. (ISDN simulators are physical devices and are plentiful on ebay – they’re no relation to “router simulators”.)
Again, I want to reiterate that you can work any Cisco router into a CCNA / CCNP home lab - there's no "right" or "wrong" combination of equipment. But as with anything else, some combinations are better than others, so consider adding some 2520s to your home lab! This router gives you a great combination of interfaces and capabilities, plus the most important factor of all - real hands-on experience during your CCNA and CCNP exam preparation!
My personal favorite is the Cisco 2520. This router has four serial interfaces, making it an ideal frame relay switch. Don't forget that just because you're using a router as a frame switch, you can still use its routing capabilities. One setup I use is to use three of the four serial interfaces for frame switching and the fourth interface as a point-to-point network with another router. All you need is some DTE/DCE cables and you're all set.
The 2520 also comes with one ethernet interface and an ISDN interface, so that gives you even more options. Even if you're not planning to run ISDN in your home lab right now, you may choose to do so in the future - and with a 2520, you've already got the right router to do so. Keep in mind that if you are going to run ISDN in your home lab, you’ll need an ISDN device such as an ISDN simulator in your lab. (ISDN simulators are physical devices and are plentiful on ebay – they’re no relation to “router simulators”.)
Again, I want to reiterate that you can work any Cisco router into a CCNA / CCNP home lab - there's no "right" or "wrong" combination of equipment. But as with anything else, some combinations are better than others, so consider adding some 2520s to your home lab! This router gives you a great combination of interfaces and capabilities, plus the most important factor of all - real hands-on experience during your CCNA and CCNP exam preparation!
Cisco CCNA / CCNP Home Lab Tutorial: Routing On A Frame Relay Switch
When you're preparing for CCNA and CCNP exam success, the best investment you can make is to put together your own home lab. There is no better way to learn Cisco technologies and prepare for the CCNA, BSCI, BCMSN, CIT, and other exams than by working with the many protocols and services you'll need to master in order to pass the exams.
One of the most popular articles I've written over the few years dealt with buying and configuring a Cisco router as a frame relay switch. That article is still available on many websites (including my own), but I want to remind you that just because you configure a router as a frame relay switch, that doesn't mean you can't use it as a home lab router, too!
The global command "frame-relay switching" allows a Cisco router such as a 2520 or 4000 to perform just that, frame relay switching, but this command doesn't disable IP routing. Depending on the router model you use, you will most likely have some extra serial connectors as well as an ethernet port that you can use with your other routers in your home lab.
Let's say you have a 2520 router as your frame relay switch. This switch has four serial ports and an AUI port. You could connect to up to four routers to the 2520's serial ports in order to serve as the frame relay switch for those other routers, and still assign an IP address to the ethernet port and run a routing protocol on the 2520. If you're connecting to less than four other routers as the frame relay switch, you can assign IP addresses to the leftover serial ports as well.
One of the most popular articles I've written over the few years dealt with buying and configuring a Cisco router as a frame relay switch. That article is still available on many websites (including my own), but I want to remind you that just because you configure a router as a frame relay switch, that doesn't mean you can't use it as a home lab router, too!
The global command "frame-relay switching" allows a Cisco router such as a 2520 or 4000 to perform just that, frame relay switching, but this command doesn't disable IP routing. Depending on the router model you use, you will most likely have some extra serial connectors as well as an ethernet port that you can use with your other routers in your home lab.
Let's say you have a 2520 router as your frame relay switch. This switch has four serial ports and an AUI port. You could connect to up to four routers to the 2520's serial ports in order to serve as the frame relay switch for those other routers, and still assign an IP address to the ethernet port and run a routing protocol on the 2520. If you're connecting to less than four other routers as the frame relay switch, you can assign IP addresses to the leftover serial ports as well.
Cisco CCNA / CCNP Home Lab Tutorial: Cabling Your Access Server
A Cisco home lab is an invaluable study tool when you're preparing for CCNA and CCNP exam success. Once you've gotten a couple of routers and switches, you'll quickly get tired of moving that blue console cable every time you want to configure a different device. The solution to this problem is purchasing and configuring an access server (AS).
For those of you new to access servers, note that these are not white boxes running Microsoft operating systems. These are Cisco routers that allow you to connect to all the routers and switches in your home lab without moving a cable. You can physically or logically connect to the access server and work with all your devices from there.
When you're pricing access servers, please remember that you do NOT need an expensive AS. Right now on ebay there are access servers costing up to $5000 - this is NOT what you want to buy. What you're looking for is something like a 2509 or 2511, which is going to run you anywhere from $100 - $200. It's money well spent, because once you get an AS, you'll really wonder how you ever did without it.
The only additional hardware you need is the cable that will physically connect your AS to the other routers and switches in your home lab. The cable you need is called an octal cable, so named because one end of this cable is actually eight ends, all terminated with a numbered RJ-45 connector.
The large end of the cable is going to be connected to the AS itself. The cable will connect to a port on the AS that will have "async 1-8" directly above the physical port. It is this port that makes an AS different from other Cisco routers.
Once you've got your AS and this cable, you're ready to configure your AS. Connect the cable to the AS as described above, and then you will connect one of the RJ-45 connectors to the console port of each one of your routers and switches. Make sure to note the number that's on the cable itself right below the connector, because that's very important. In the next part of this home lab tutorial, I'll tell you exactly how to configure your access server for best results, along with a few troubleshooting tips.
For those of you new to access servers, note that these are not white boxes running Microsoft operating systems. These are Cisco routers that allow you to connect to all the routers and switches in your home lab without moving a cable. You can physically or logically connect to the access server and work with all your devices from there.
When you're pricing access servers, please remember that you do NOT need an expensive AS. Right now on ebay there are access servers costing up to $5000 - this is NOT what you want to buy. What you're looking for is something like a 2509 or 2511, which is going to run you anywhere from $100 - $200. It's money well spent, because once you get an AS, you'll really wonder how you ever did without it.
The only additional hardware you need is the cable that will physically connect your AS to the other routers and switches in your home lab. The cable you need is called an octal cable, so named because one end of this cable is actually eight ends, all terminated with a numbered RJ-45 connector.
The large end of the cable is going to be connected to the AS itself. The cable will connect to a port on the AS that will have "async 1-8" directly above the physical port. It is this port that makes an AS different from other Cisco routers.
Once you've got your AS and this cable, you're ready to configure your AS. Connect the cable to the AS as described above, and then you will connect one of the RJ-45 connectors to the console port of each one of your routers and switches. Make sure to note the number that's on the cable itself right below the connector, because that's very important. In the next part of this home lab tutorial, I'll tell you exactly how to configure your access server for best results, along with a few troubleshooting tips.
Tuesday, December 23, 2008
Cisco CCNA / CCNP Certification Tutorial: Frame Relay End-To-End Keepalives
One of the first things you learned about Frame is that the LMI also serves as a keepalive, or a heartbeat - and if three consecutive LMIs are missed, the line protocol goes down. There's a limitation to LMI as a keepalive, though. The LMI is exchanged only between the DTE and the closest DCE. The LMI is therefore a local keepalive that does not reflect any possible issues on the remote end of the virtual circuit.
Taking the LMI concept to the next logical level, Frame Relay End-To-End Keepalives (FREEK, one of the least-heard Cisco acronyms for some reason) are used to verify that endpoint-to-endpoint communications are functioning properly.
What you have to keep in mind about FREEK is that each and every PVC needs two separate keepalive processes. Remember, with a PVC, there's no guarantee that the path taking through the frame relay cloud to get from R1 to R2 is going to be the same path taken to go back from R2 to R1. One process will be used to send requests for information and handle the responses to these requests; this is the send side. When the send side transmits a keepalive request, a response is expected in a certain number of seconds. If one is not received, an error event is noted. If enough error events are recorded, the VC's keepalive status is marked as down.
The process that responds to the other side's requests is the receive side.
This being Cisco, we've got to have some modes, right? FREEK has four operational modes.
Bidirectional mode enables both the send and receive process enabled on the router, meaning that the router will send requests and process responses (send side) and will also respond to remote requests for information (receive side).
Request mode enables only the send process. The router will send requests and process responses to those requests, but will not answer requests from other routers.
Reply mode enables only the receive process. The router will respond to requests from other routers but will initiate no requests of its own.
Finally, passive reply mode allows the router to respond to requests, but no timers are set and no events are tracked.
Frame Relay End-To-End Keepalive defaults:
Two send or receive errors must be registered in order for the VC to be considered down.
The event window size is three. The event window is the number of events considered by the router when determining the status of the VC. Therefore, using the defaults, two send or receive errors would have to be received within the event window of three events for the VC to be considered down.
The timer mentioned earlier - the amount of time a router waits for a response - is set to 10 seconds
Working with Frame Relay end-to-end keepalives is just one Frame skill you’ll need to pass the CCNP exams – and I wouldn’t be surprised to see them on a CCIE exam. Know the details and you’re on your way to Cisco certification exam success!
Taking the LMI concept to the next logical level, Frame Relay End-To-End Keepalives (FREEK, one of the least-heard Cisco acronyms for some reason) are used to verify that endpoint-to-endpoint communications are functioning properly.
What you have to keep in mind about FREEK is that each and every PVC needs two separate keepalive processes. Remember, with a PVC, there's no guarantee that the path taking through the frame relay cloud to get from R1 to R2 is going to be the same path taken to go back from R2 to R1. One process will be used to send requests for information and handle the responses to these requests; this is the send side. When the send side transmits a keepalive request, a response is expected in a certain number of seconds. If one is not received, an error event is noted. If enough error events are recorded, the VC's keepalive status is marked as down.
The process that responds to the other side's requests is the receive side.
This being Cisco, we've got to have some modes, right? FREEK has four operational modes.
Bidirectional mode enables both the send and receive process enabled on the router, meaning that the router will send requests and process responses (send side) and will also respond to remote requests for information (receive side).
Request mode enables only the send process. The router will send requests and process responses to those requests, but will not answer requests from other routers.
Reply mode enables only the receive process. The router will respond to requests from other routers but will initiate no requests of its own.
Finally, passive reply mode allows the router to respond to requests, but no timers are set and no events are tracked.
Frame Relay End-To-End Keepalive defaults:
Two send or receive errors must be registered in order for the VC to be considered down.
The event window size is three. The event window is the number of events considered by the router when determining the status of the VC. Therefore, using the defaults, two send or receive errors would have to be received within the event window of three events for the VC to be considered down.
The timer mentioned earlier - the amount of time a router waits for a response - is set to 10 seconds
Working with Frame Relay end-to-end keepalives is just one Frame skill you’ll need to pass the CCNP exams – and I wouldn’t be surprised to see them on a CCIE exam. Know the details and you’re on your way to Cisco certification exam success!
Cisco CCNA / CCNP Certification Exam Lab: Frame Relay Subinterfaces And Split Horizon
Earning your Cisco CCNA and CCNP is a tough proposition, and part of that is the fact that you quickly learn that there’s usually more than one way to do things with Cisco routers – and while that’s generally a good thing, you better know the ins and outs of all options when it comes to test day and working on production networks. Working with Frame Relay subinterfaces and split horizon is just one such situation.
One reason for the use of subinterfaces is to circumvent the rule of split horizon. You recall from your CCNA studies that split horizon dictates that a route cannot be advertised out the same interface upon which it was learned in the first place. In the following example, R1 is the hub and R2 and R3 are the spokes. All three routers are using their physical interfaces for frame relay connectivity, and they are also running RIPv2 172.12.123.0 /24. Each router is also advertising a loopback interface, using the router number for each octet.
R1(config)#int s0
R1(config-if)#ip address 172.12.123.1 255.255.255.0
R1(config-if)#no frame inverse
R1(config-if)#frame map ip 172.12.123.2 122 broadcast
R1(config-if)#frame map ip 172.12.123.3 123 broadcast
R1(config-if)#no shut
R2(config)#int s0
R2(config-if)#encap frame
R2(config-if)#no frame inver
R2(config-if)#frame map ip 172.12.123.1 221 broadcast
R2(config-if)#frame map ip 172.12.123.3 221 broadcast
R2(config-if)#ip address 172.12.123.2 255.255.255.0
R3(config)#int s0
R3(config-if)#encap frame
R3(config-if)#no frame inver
R3(config-if)#frame map ip 172.12.123.1 321 broadcast
R3(config-if)#frame map ip 172.12.123.2 321 broadcast
R3(config-if)#ip address 172.12.123.3 255.255.255.0
R1#show ip route rip
2.0.0.0/32 is subnetted, 1 subnets
R 2.2.2.2 [120/1] via 172.12.123.2, 00:00:20, Serial0
3.0.0.0/32 is subnetted, 1 subnets
R 3.3.3.3 [120/1] via 172.12.123.3, 00:00:22, Serial0
R2#show ip route rip
1.0.0.0/32 is subnetted, 1 subnets
R 1.1.1.1 [120/1] via 172.12.123.1, 00:00:06, Serial0
R3#show ip route rip
1.0.0.0/32 is subnetted, 1 subnets
R 1.1.1.1 [120/1] via 172.12.123.1, 00:00:04, Serial0
The hub router R1 has a route to both loopbacks, but neither spoke has a route to the other spoke's loopback. That's because split horizon prevents R1 from advertising a network via Serial0 if the route was learned on Serial0 to begin with.
We've got two options here, one of which is to disable spilt horizon on the interface. While doing so will have the desired effect in our little network, disabling split horizon is not a good idea and should be avoided whenever possible. We’re not going to do it in this lab, but here is the syntax to do so:
R1(config)#interface serial0
R1(config-if)#no ip split-horizon
A better solution is to configure subinterfaces on R1. The IP addressing will have to be revisited, but that's no problem here. R1 and R2 will use 172.12.123.0 /24 to communicate, while R1 and R3 will use 172.12.13.0 /24. R3's serial0 interface will need to be renumbered, so let's look at all three router configurations:
R1(config)#interface serial0
R1(config-if)#encap frame
R1(config-if)#no frame inverse-arp
R1(config-if)#no ip address
R1(config-if)#interface serial0.12 multipoint
R1(config-subif)#ip address 172.12.123.1 255.255.255.0
R1(config-subif)#frame map ip 172.12.123.2 122 broadcast
R1(config-subif)#interface serial0.31 point-to-point
R1(config-subif)#ip address 172.12.13.1 255.255.255.0
R1(config-subif)#frame interface-dlci 123
R2(config)#int s0
R2(config-if)#ip address 172.12.123.2 255.255.255.0
R2(config-if)#encap frame
R2(config-if)#frame map ip 172.12.13.3 221 broadcast
R2(config-if)#frame map ip 172.12.123.1 221 broadcast
R3(config)#int s0
R3(config-if)#ip address 172.12.13.3 255.255.255.0
R3(config-if)#encap frame
R3(config-if)#frame map ip 172.12.13.1 321 broadcast
R3(config-if)#frame map ip 172.12.123.2 321 broadcast
A frame map statement always names the REMOTE IP address and the LOCAL DLCI. Don't forget the broadcast option!
Show frame map shows us that all the static mappings on R1 are up and running. Note the "static" output, which indicates these mappings are a result of using the frame map command. Pings are not shown, but all three routers can ping each other at this point.
R1#show frame map
Serial0 (up): ip 172.12.123.2 dlci 122(0x7A,0x1CA0), static,
broadcast, CISCO, status defined, active
Serial0 (up): ip 172.12.13.3 dlci 123(0x7B,0x1CB0), static,
broadcast, CISCO, status defined, active
After the 172.12.13.0 /24 network is added to R1 and R3’s RIP configuration, R2 and R3 now have each other's loopback network in their RIP routing tables.
R2#show ip route rip
1.0.0.0/32 is subnetted, 1 subnets
R 1.1.1.1 [120/1] via 172.12.123.1, 00:00:20, Serial0
3.0.0.0/32 is subnetted, 1 subnets
R 3.3.3.3 [120/1] via 172.12.123.1, 00:00:22, Serial0
R3#show ip route rip
1.0.0.0/32 is subnetted, 1 subnets
R 1.1.1.1 [120/1] via 172.12.13.1, 00:00:20, Serial0
2.0.0.0/32 is subnetted, 1 subnets
R 2.2.2.2 [120/1] via 172.12.13.1, 00:00:22, Serial0
While turning split horizon off is one way to achieve total IP connectivity, doing so can have other unintended results. The use of subinterfaces is a more effective way of allowing the spokes to see the hub's loopback network.
One reason for the use of subinterfaces is to circumvent the rule of split horizon. You recall from your CCNA studies that split horizon dictates that a route cannot be advertised out the same interface upon which it was learned in the first place. In the following example, R1 is the hub and R2 and R3 are the spokes. All three routers are using their physical interfaces for frame relay connectivity, and they are also running RIPv2 172.12.123.0 /24. Each router is also advertising a loopback interface, using the router number for each octet.
R1(config)#int s0
R1(config-if)#ip address 172.12.123.1 255.255.255.0
R1(config-if)#no frame inverse
R1(config-if)#frame map ip 172.12.123.2 122 broadcast
R1(config-if)#frame map ip 172.12.123.3 123 broadcast
R1(config-if)#no shut
R2(config)#int s0
R2(config-if)#encap frame
R2(config-if)#no frame inver
R2(config-if)#frame map ip 172.12.123.1 221 broadcast
R2(config-if)#frame map ip 172.12.123.3 221 broadcast
R2(config-if)#ip address 172.12.123.2 255.255.255.0
R3(config)#int s0
R3(config-if)#encap frame
R3(config-if)#no frame inver
R3(config-if)#frame map ip 172.12.123.1 321 broadcast
R3(config-if)#frame map ip 172.12.123.2 321 broadcast
R3(config-if)#ip address 172.12.123.3 255.255.255.0
R1#show ip route rip
2.0.0.0/32 is subnetted, 1 subnets
R 2.2.2.2 [120/1] via 172.12.123.2, 00:00:20, Serial0
3.0.0.0/32 is subnetted, 1 subnets
R 3.3.3.3 [120/1] via 172.12.123.3, 00:00:22, Serial0
R2#show ip route rip
1.0.0.0/32 is subnetted, 1 subnets
R 1.1.1.1 [120/1] via 172.12.123.1, 00:00:06, Serial0
R3#show ip route rip
1.0.0.0/32 is subnetted, 1 subnets
R 1.1.1.1 [120/1] via 172.12.123.1, 00:00:04, Serial0
The hub router R1 has a route to both loopbacks, but neither spoke has a route to the other spoke's loopback. That's because split horizon prevents R1 from advertising a network via Serial0 if the route was learned on Serial0 to begin with.
We've got two options here, one of which is to disable spilt horizon on the interface. While doing so will have the desired effect in our little network, disabling split horizon is not a good idea and should be avoided whenever possible. We’re not going to do it in this lab, but here is the syntax to do so:
R1(config)#interface serial0
R1(config-if)#no ip split-horizon
A better solution is to configure subinterfaces on R1. The IP addressing will have to be revisited, but that's no problem here. R1 and R2 will use 172.12.123.0 /24 to communicate, while R1 and R3 will use 172.12.13.0 /24. R3's serial0 interface will need to be renumbered, so let's look at all three router configurations:
R1(config)#interface serial0
R1(config-if)#encap frame
R1(config-if)#no frame inverse-arp
R1(config-if)#no ip address
R1(config-if)#interface serial0.12 multipoint
R1(config-subif)#ip address 172.12.123.1 255.255.255.0
R1(config-subif)#frame map ip 172.12.123.2 122 broadcast
R1(config-subif)#interface serial0.31 point-to-point
R1(config-subif)#ip address 172.12.13.1 255.255.255.0
R1(config-subif)#frame interface-dlci 123
R2(config)#int s0
R2(config-if)#ip address 172.12.123.2 255.255.255.0
R2(config-if)#encap frame
R2(config-if)#frame map ip 172.12.13.3 221 broadcast
R2(config-if)#frame map ip 172.12.123.1 221 broadcast
R3(config)#int s0
R3(config-if)#ip address 172.12.13.3 255.255.255.0
R3(config-if)#encap frame
R3(config-if)#frame map ip 172.12.13.1 321 broadcast
R3(config-if)#frame map ip 172.12.123.2 321 broadcast
A frame map statement always names the REMOTE IP address and the LOCAL DLCI. Don't forget the broadcast option!
Show frame map shows us that all the static mappings on R1 are up and running. Note the "static" output, which indicates these mappings are a result of using the frame map command. Pings are not shown, but all three routers can ping each other at this point.
R1#show frame map
Serial0 (up): ip 172.12.123.2 dlci 122(0x7A,0x1CA0), static,
broadcast, CISCO, status defined, active
Serial0 (up): ip 172.12.13.3 dlci 123(0x7B,0x1CB0), static,
broadcast, CISCO, status defined, active
After the 172.12.13.0 /24 network is added to R1 and R3’s RIP configuration, R2 and R3 now have each other's loopback network in their RIP routing tables.
R2#show ip route rip
1.0.0.0/32 is subnetted, 1 subnets
R 1.1.1.1 [120/1] via 172.12.123.1, 00:00:20, Serial0
3.0.0.0/32 is subnetted, 1 subnets
R 3.3.3.3 [120/1] via 172.12.123.1, 00:00:22, Serial0
R3#show ip route rip
1.0.0.0/32 is subnetted, 1 subnets
R 1.1.1.1 [120/1] via 172.12.13.1, 00:00:20, Serial0
2.0.0.0/32 is subnetted, 1 subnets
R 2.2.2.2 [120/1] via 172.12.13.1, 00:00:22, Serial0
While turning split horizon off is one way to achieve total IP connectivity, doing so can have other unintended results. The use of subinterfaces is a more effective way of allowing the spokes to see the hub's loopback network.
Cisco CCNA / CCNP Certification Exam: Frame Relay BECNs and FECNs
BECNs and FECNs aren't just important to know for your Cisco CCNA and CCNP certification exams - they're an important part of detecting congestion on a Frame Relay network and allowing the network to dynamically adjust its transmission rate when congestion is encountered.
The Forward Explicit Congestion Notification (FECN, pronounced "feckon") bit is set to zero by default, and will be set to 1 if congestion was experienced by the frame in the direction in which the frame was traveling. A DCE (frame relay switch) will set this bit, and a DTE (router) will receive it, and see that congestion was encountered along the frame's path.
If network congestion exists in the opposite direction in which the frame was traveling, the Backward Explicit Congestion Notification (BECN, pronounced "beckon") will be set to 1 by a DCE.
If this is your first time working with BECNs and FECNs, you might wonder why the BECN even exists - after all, why send a "backwards" notification? The BECN is actually the most important part of this entire process, since it's the BECN bit that indicates to the sender that it needs to slow down!
For example, frames sent from Kansas City to Green Bay encounter congestion in the FR cloud. A Frame Switch sets the FECN bit to 1. In order to alert KC that it's sending data too fast, GB will send return frames with the BECN bit set. When KC sees the BECN bit is set to 1, the KC router knows that the congestion occurred when frames were sent from KC to GB.
Frame Relay BECN Adaptive Shaping allows a router to dynamically throttle back on its transmission rate if it receives frames from the remote host with the BECN bit set. In this case, KC sees that the traffic it's sending to GB is encountering congestion, because the traffic coming back from GB has the BECN bit set. If BECN Adaptive Shaping is running on KC, that router will adjust to this congestion by slowing its transmission rate. When the BECNs stop coming in from GB, KC will begin to send at a faster rate.
BECN Adaptive Shaping is configured as follows:
KC(config)#int s0
KC(config-if)#frame-relay adaptive-shaping becn
To see how many frames are coming in and going out with the BECN and FECN bits set, run show frame pvc.
R3#show frame pvc
< some output removed for clarity >
input pkts 306 output pkts 609 in bytes 45566
out bytes 79364 dropped pkts 0 in FECN pkts 0
in BECN pkts 0 out FECN pkts 0 out BECN pkts 0
in DE pkts 0 out DE pkts 0
out bcast pkts 568 out bcast bytes 75128
pvc create time 01:26:27, last time pvc status changed 01:26:27
Just watch the "in"s and "out"s of BECN, FECN, and DE in both the exam room and your production networks!
The Forward Explicit Congestion Notification (FECN, pronounced "feckon") bit is set to zero by default, and will be set to 1 if congestion was experienced by the frame in the direction in which the frame was traveling. A DCE (frame relay switch) will set this bit, and a DTE (router) will receive it, and see that congestion was encountered along the frame's path.
If network congestion exists in the opposite direction in which the frame was traveling, the Backward Explicit Congestion Notification (BECN, pronounced "beckon") will be set to 1 by a DCE.
If this is your first time working with BECNs and FECNs, you might wonder why the BECN even exists - after all, why send a "backwards" notification? The BECN is actually the most important part of this entire process, since it's the BECN bit that indicates to the sender that it needs to slow down!
For example, frames sent from Kansas City to Green Bay encounter congestion in the FR cloud. A Frame Switch sets the FECN bit to 1. In order to alert KC that it's sending data too fast, GB will send return frames with the BECN bit set. When KC sees the BECN bit is set to 1, the KC router knows that the congestion occurred when frames were sent from KC to GB.
Frame Relay BECN Adaptive Shaping allows a router to dynamically throttle back on its transmission rate if it receives frames from the remote host with the BECN bit set. In this case, KC sees that the traffic it's sending to GB is encountering congestion, because the traffic coming back from GB has the BECN bit set. If BECN Adaptive Shaping is running on KC, that router will adjust to this congestion by slowing its transmission rate. When the BECNs stop coming in from GB, KC will begin to send at a faster rate.
BECN Adaptive Shaping is configured as follows:
KC(config)#int s0
KC(config-if)#frame-relay adaptive-shaping becn
To see how many frames are coming in and going out with the BECN and FECN bits set, run show frame pvc.
R3#show frame pvc
< some output removed for clarity >
input pkts 306 output pkts 609 in bytes 45566
out bytes 79364 dropped pkts 0 in FECN pkts 0
in BECN pkts 0 out FECN pkts 0 out BECN pkts 0
in DE pkts 0 out DE pkts 0
out bcast pkts 568 out bcast bytes 75128
pvc create time 01:26:27, last time pvc status changed 01:26:27
Just watch the "in"s and "out"s of BECN, FECN, and DE in both the exam room and your production networks!
Cisco CCNA / CCNP Certification Exam: Frame Relay Encapsulation Types
When you're studying to pass the Cisco CCNA and CCNP certification exams, you quickly learn that there's always something else to learn. (You'll really pick up on this in your CCIE studies, trust me!) Today we'll take a look at an often-overlooked topic in Frame Relay, the encapsulation type. You don't exactly change this on a daily basis in production networks (not if you want to stay employed, anyway!), but it's an important exam topic that you must be familiar with.
The DCE and DTE must agree on the LMI type, but there's another value that must be agreed upon by the two DTEs serving as the endpoints of the VC. The Frame encapsulation can be left at the default of Cisco (which is Cisco-proprietary), or it can be changed to the industry-standard IETF, as shown below. If a non-Cisco router is the remote endpoint, IETF encapsulation must be used. Note that the default of Cisco isn't listed as an option by IOS Help, so you better know that one by heart!
R1(config)#int s0
R1(config-if)#encap frame ?
ietf Use RFC1490/RFC2427 encapsulation
R1(config-if)#encap frame ietf
What if a physical interface is in use and some remote hosts require Cisco encapsulation and others require IETF? The encapsulation type can be configured on a per-PVC basis as well. One encap type can be used on the interface, and any map statements that require a different encap type can have that specified in the appropriate map statement. In the following example, all PVCs will use the default Cisco encapsulation type except for PVC 115. The frame map statement using that PVC has ietf specified.
R1(config)#int s0/0
R1(config-if)#encap frame
R1(config-if)#frame map ip 172.12.123.3 123 broadcast
R1(config-if)#frame map ip 172.12.123.2 122 ietf broadcast
show frame map shows us that the mapping to DLCI 123 is using Cisco encapsulation, and DLCI 122 is using IETF.
R1#show frame map
Serial0 (up): ip 172.12.123.3 dlci 123(0x7B,0x1CB0), static
broadcast, CISCO, status defined, active
Serial0 (up): ip 172.12.123.2 dlci 122(0x7B,0x1CB0), static
broadcast, ietf, status defined, active
Just remember that Cisco is the default, and all PVCs will use Cisco unless you specify IETF in the frame map statement itself. You could also change the entire interface to use IETF for all mappings with the frame-relay encapsulation IETF command. For Cisco exams, as well as work on production networks, it's always a good idea to know more than one way to do something!
The DCE and DTE must agree on the LMI type, but there's another value that must be agreed upon by the two DTEs serving as the endpoints of the VC. The Frame encapsulation can be left at the default of Cisco (which is Cisco-proprietary), or it can be changed to the industry-standard IETF, as shown below. If a non-Cisco router is the remote endpoint, IETF encapsulation must be used. Note that the default of Cisco isn't listed as an option by IOS Help, so you better know that one by heart!
R1(config)#int s0
R1(config-if)#encap frame ?
ietf Use RFC1490/RFC2427 encapsulation
R1(config-if)#encap frame ietf
What if a physical interface is in use and some remote hosts require Cisco encapsulation and others require IETF? The encapsulation type can be configured on a per-PVC basis as well. One encap type can be used on the interface, and any map statements that require a different encap type can have that specified in the appropriate map statement. In the following example, all PVCs will use the default Cisco encapsulation type except for PVC 115. The frame map statement using that PVC has ietf specified.
R1(config)#int s0/0
R1(config-if)#encap frame
R1(config-if)#frame map ip 172.12.123.3 123 broadcast
R1(config-if)#frame map ip 172.12.123.2 122 ietf broadcast
show frame map shows us that the mapping to DLCI 123 is using Cisco encapsulation, and DLCI 122 is using IETF.
R1#show frame map
Serial0 (up): ip 172.12.123.3 dlci 123(0x7B,0x1CB0), static
broadcast, CISCO, status defined, active
Serial0 (up): ip 172.12.123.2 dlci 122(0x7B,0x1CB0), static
broadcast, ietf, status defined, active
Just remember that Cisco is the default, and all PVCs will use Cisco unless you specify IETF in the frame map statement itself. You could also change the entire interface to use IETF for all mappings with the frame-relay encapsulation IETF command. For Cisco exams, as well as work on production networks, it's always a good idea to know more than one way to do something!
Monday, December 22, 2008
CCNA / CCNP Home Lab Tutorial: Assembling Your Cisco Home Lab
A CCNA or CCNP candidate who wants to be totally prepared for their exams is going to put together a home lab to practice on. With used Cisco routers and switches more affordable and plentiful then ever before, there's really no excuse to not have one!
With the many different models available, there is some understandable confusion among future CCNAs and CCNPs about which routers to buy and which ones to avoid. You can take almost any set of Cisco routers and put together a home lab; part of the learning process is taking what equipment you have available and putting together your own lab! For those of you preparing to start your home lab or add to your existing one, this article will list the routers I use in my Cisco pods. You certainly don't have to have all this equipment, but this will give you some good ideas on how to get started.
The most versatile router you can get for your CCNA / CCNP home lab is a 2520. These routers come with four serial ports, one ethernet port, and one BRI interface for ISDN practice. This mix of interfaces means you can actually use it as a frame relay switch while using the ethernet and BRI ports for routing. (There is no problem with using a lab router as both your frame relay switch and a practice router; for a frame relay switch sample configuration, visit my website!)
My pods consist of five routers and two switches, and three of the five routers are 2520s, due to their versatility. A recent ebay search showed these routers selling for $99 - $125, an outstanding value for the practice you're going to get.
I also use 2501s in my home labs. These have fewer interfaces, but the combination of two serial interfaces and one ethernet interface allows you to get plenty of practice.
A combination that works very well is using three 2520s; one as my dedicated frame relay switch, one as R1, and another as R2. Add a 2501 as R3, and you can have a frame cloud connecting R1, R2, and R3, a direct serial connection between R1 and R3, an Ethernet segment that includes all three routers, and an ISDN connection between R1 and R2 if you have an ISDN simulator. That combination will allow you to get a tremendous amount of practice for the exams, and you can always sell it when you're done!
2501s are very affordable, with many in the $50 range on ebay. It's quite possible to get three 2520s and one 2501 for less than $500 total, and you can get most of that money back if you choose to sell it when you're done.
With four routers to work with, you're probably going to get tired of moving that console cable around. An access server (actually a Cisco router, not the white boxes we tend to think of when we hear "server") will help you out with that. An access server allows you to set up a connection with each of your other routers via an octal cable, which prevents you from moving that console cable around continually. For an example of an access server configuration, just visit my website and look in the "Free Training" section.
Access server prices vary quite a bit; don't panic if you do an ebay search and see them costing thousands of dollars. You do NOT need an expensive access server for your CCNA / CCNP home lab. 2511s are great routers to get for your access server.
One question I get often from CCNA / CCNP candidates is "What routers should I buy that I can still use when I'm ready to study for the CCNP?" The CCIE lab changes regularly and sometimes drastically when it comes to the equipment you'll need. During my CCIE lab studies, I found that renting time from online rack rental providers was actually the best way to go. Don't hesitate when putting your CCNA / CCNP home lab together, wondering what will be acceptable for the CCIE lab a year or so from now. None of us know what's going to be on that equipment list, so get the CCNA and CCNP first - by building your own Cisco home lab!
With the many different models available, there is some understandable confusion among future CCNAs and CCNPs about which routers to buy and which ones to avoid. You can take almost any set of Cisco routers and put together a home lab; part of the learning process is taking what equipment you have available and putting together your own lab! For those of you preparing to start your home lab or add to your existing one, this article will list the routers I use in my Cisco pods. You certainly don't have to have all this equipment, but this will give you some good ideas on how to get started.
The most versatile router you can get for your CCNA / CCNP home lab is a 2520. These routers come with four serial ports, one ethernet port, and one BRI interface for ISDN practice. This mix of interfaces means you can actually use it as a frame relay switch while using the ethernet and BRI ports for routing. (There is no problem with using a lab router as both your frame relay switch and a practice router; for a frame relay switch sample configuration, visit my website!)
My pods consist of five routers and two switches, and three of the five routers are 2520s, due to their versatility. A recent ebay search showed these routers selling for $99 - $125, an outstanding value for the practice you're going to get.
I also use 2501s in my home labs. These have fewer interfaces, but the combination of two serial interfaces and one ethernet interface allows you to get plenty of practice.
A combination that works very well is using three 2520s; one as my dedicated frame relay switch, one as R1, and another as R2. Add a 2501 as R3, and you can have a frame cloud connecting R1, R2, and R3, a direct serial connection between R1 and R3, an Ethernet segment that includes all three routers, and an ISDN connection between R1 and R2 if you have an ISDN simulator. That combination will allow you to get a tremendous amount of practice for the exams, and you can always sell it when you're done!
2501s are very affordable, with many in the $50 range on ebay. It's quite possible to get three 2520s and one 2501 for less than $500 total, and you can get most of that money back if you choose to sell it when you're done.
With four routers to work with, you're probably going to get tired of moving that console cable around. An access server (actually a Cisco router, not the white boxes we tend to think of when we hear "server") will help you out with that. An access server allows you to set up a connection with each of your other routers via an octal cable, which prevents you from moving that console cable around continually. For an example of an access server configuration, just visit my website and look in the "Free Training" section.
Access server prices vary quite a bit; don't panic if you do an ebay search and see them costing thousands of dollars. You do NOT need an expensive access server for your CCNA / CCNP home lab. 2511s are great routers to get for your access server.
One question I get often from CCNA / CCNP candidates is "What routers should I buy that I can still use when I'm ready to study for the CCNP?" The CCIE lab changes regularly and sometimes drastically when it comes to the equipment you'll need. During my CCIE lab studies, I found that renting time from online rack rental providers was actually the best way to go. Don't hesitate when putting your CCNA / CCNP home lab together, wondering what will be acceptable for the CCIE lab a year or so from now. None of us know what's going to be on that equipment list, so get the CCNA and CCNP first - by building your own Cisco home lab!
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