Learning IPv6 is paramount in your efforts to pass the BSCI exam and go on to earn your CCNP, and it's going to help in your real-world networking career as well. IPv6 can be confusing at first, but it's like anything else in Cisco or networking as a whole - learn one part at a time, master the fundamentals, and you're on your way to success. In today's article we're going to take a look at IPv6 address types.
In IPv4, a unicast address is simply an address used to represent a single host, where multicast addresses represent a group of hosts and broadcasts represent all hosts.
In IPv6, it's not quite that simple. There are actually different types of unicast addresses, each with its own separate function. This allows IPv6 to get data where it's supposed to go quicker than IPv4 while conserving router resources.
IPv6 offers two kinds of local addresses, link-local and site-local. Site-local addresses allow devices in the same organization, or site, to exchange data. Site-local addresses are IPv6's equivalent to IPv4's private address classes, since hosts using them are able to communicate with each other throughout the organization, but these addresses cannot be used to reach Internet hosts.
Site-local and link-local addresses are actually derived from a host's MAC address. Therefore, if HostA has HostB's IPv6 address, HostA can determine HostB's MAC address from that, making ARP unnecessary.
Link-local addresses have a smaller scope than site-local. Link-local addresses are just that, local to a physical link. These particular addresses are not used at all in forwarding data. One use for these addresses is Neighbor Discovery, which is IPv6's answer to ARP.
You can identify these and other IPv6 addresses by their initial bits:
001 - Global address
(first 96 bits set to zero) - IPv4-compatible address
1111 1111 – Multicast
1111 1110 11 - Site local
1111 1110 10 - Link Local
As a future CCNP, you're more than familiar with the reserved IPv4 address classes. You also know that they're not exactly contiguous. The developers of IPv6 took a structured approach to IPv6 reserved addresses - any address that begins with "0000 0000" is an IPv6 reserved address. One of these is the IPv6 loopback address, and this will give you some practice with your zero compression!
IP v6 Loopback: 0000:0000:0000:0000:0000:0000:0000:0001
Using Leading Zero Compression Only: 0:0:0:0:0:0:0:1
Combining Leading Zero and Zero Compression: ::1
Zero compression looks pretty good now, doesn't it? You just have to get used to it and keep the rules in mind. You can use all the leading zero compression you want, but zero compression ("double-colon") can only be used once in a single address.
IPv6 is here to stay, not only on your BSCI and CCNP exams, but in the real world as well. Learning it now will not only aid you in passing your Cisco exams, but in supporting IPv6 in the future.
Showing posts with label multicast. Show all posts
Showing posts with label multicast. Show all posts
Thursday, December 25, 2008
Cisco CCNP / BCMSN Exam Tutorial: Static VLANs
BCMSN exam success and earning your CCNP certification requires you to add to your knowledge of VLAN configuration. When you studied for your CCNA exam, you learned how to place ports into a VLAN and what the purpose of VLANs was, but you may not be aware that there are two types of VLAN membership. To pass the BCMSN exam, you must know the details of both types.
In this tutorial, we'll take a look at the VLAN type you are most familiar with, the "static VLAN". As you know, VLANs are a great way to create smaller broadcast domains in your network. Host devices connected to a port belonging to one VLAN will receive broadcasts and multicasts only if they were originated by another host in that same VLAN. The drawback is that without the help of a Layer 3 switch or a router, inter-VLAN communication cannot occur.
The actual configuration of a static VLAN is simple enough. In this example, by placing switch ports 0/1 and 0/2 into VLAN 12, the only broadcasts and multicasts hosts connected to those ports will receive are the ones transmitted by ports in VLAN 12.
SW1(config)#int fast 0/1
SW1(config-if)#switchport mode access
SW1(config-if)#switchport access vlan 12
% Access VLAN does not exist. Creating vlan 12
SW1(config-if)#int fast 0/2
SW1(config-if)#switchport mode access
SW1(config-if)#switchport access vlan 12
One of the many things I love about Cisco switches and routers is that if you have forgotten to do something, the Cisco device is generally going to remind you or in this case actually do it for you. I placed port 0/1 into a VLAN that did not yet exist, so the switch created it for me!
There are two commands needed to place a port into a VLAN. By default, these ports are running in dynamic desirable trunking mode, meaning that the port is actively attempting to form a trunk with a remote switch in order to send traffic between the two switches. The problem is that a trunk port belongs to all VLANs by default, and we want to put this port into a single VLAN only. To do so, we run the switchport mode access command to make the port an access port, and access ports belong to one and only one VLAN. After doing that, we placed the port into VLAN 12 with the switchport access vlan 12 command. Running the switchport mode access command effectively turns trunking off on that port.
The hosts are unaware of VLANs; they simply assume the VLAN membership of the port they're connected to. But that's not quite the case with dynamic VLANs, which we'll examine in the next part of this BCMSN tutorial.
In this tutorial, we'll take a look at the VLAN type you are most familiar with, the "static VLAN". As you know, VLANs are a great way to create smaller broadcast domains in your network. Host devices connected to a port belonging to one VLAN will receive broadcasts and multicasts only if they were originated by another host in that same VLAN. The drawback is that without the help of a Layer 3 switch or a router, inter-VLAN communication cannot occur.
The actual configuration of a static VLAN is simple enough. In this example, by placing switch ports 0/1 and 0/2 into VLAN 12, the only broadcasts and multicasts hosts connected to those ports will receive are the ones transmitted by ports in VLAN 12.
SW1(config)#int fast 0/1
SW1(config-if)#switchport mode access
SW1(config-if)#switchport access vlan 12
% Access VLAN does not exist. Creating vlan 12
SW1(config-if)#int fast 0/2
SW1(config-if)#switchport mode access
SW1(config-if)#switchport access vlan 12
One of the many things I love about Cisco switches and routers is that if you have forgotten to do something, the Cisco device is generally going to remind you or in this case actually do it for you. I placed port 0/1 into a VLAN that did not yet exist, so the switch created it for me!
There are two commands needed to place a port into a VLAN. By default, these ports are running in dynamic desirable trunking mode, meaning that the port is actively attempting to form a trunk with a remote switch in order to send traffic between the two switches. The problem is that a trunk port belongs to all VLANs by default, and we want to put this port into a single VLAN only. To do so, we run the switchport mode access command to make the port an access port, and access ports belong to one and only one VLAN. After doing that, we placed the port into VLAN 12 with the switchport access vlan 12 command. Running the switchport mode access command effectively turns trunking off on that port.
The hosts are unaware of VLANs; they simply assume the VLAN membership of the port they're connected to. But that's not quite the case with dynamic VLANs, which we'll examine in the next part of this BCMSN tutorial.
Wednesday, December 24, 2008
Cisco CCNA Certification: Broadcasts, Unicasts, And Multicasts
When you begin your CCNA studies, you get hit with a lot of different networking terms right away that you might not be familiar with. What makes it a little more confusing is that a lot of these terms sound a lot alike. Here, we're going to discuss the differences between broadcasts, multicasts, and unicasts at both the Data Link (Layer 2) and Network (Layer 3) layers of the OSI model.
A broadcast is simply a unit of information that every other device on the segment will receive. A broadcast is indicated by having every bit of the address set to its highest possible value. Since a hexadecimal bit's highest value is "f", a hexadecimal broadcast is ff-ff-ff-ff-ff-ff (or FF-FF-FF-FF-FF-FF, as the upper case does not affect hex value). The CCNA exam will demand you be very familiar with hex conversions, so if you're not comfortable with these conversions, get comfortable with them before taking the exam!
At layer 3, a broadcast is indicated by setting every bit in the 32-bit binary string to "1", making the dotted decimal value 255.255.255.255. Every host on a segment will receive such a broadcast. (Keep in mind that switches will forward a broadcast, but routers do not.) In contrast to a broadcast, a unicast is a packet or frame with only one destination.
There is a middle ground between broadcasts and unicasts, and that is a multicast. Where a broadcast will be received by all, and a unicast is received by only one host, a multicast will be received by multiple hosts, all belonging to a "multicast group". As you climb the Cisco certification pyramid, you'll be introduced to creating multicast groups and controlling multicast traffic, but for your CCNA studies you need only keep certain multicast groups in mind.
Class D addresses are reserved for multicasting this range is 224.0.0.0 - 239.255.255.255. The addresses 224.0.0.0 - 224.255.255.255 are reserved for use by network protocols on a local network segment, and like broadcasts, routers will not forward these multicast packets. (Packets with these addresses are sent with a Time To Live of 1.)
As a CCNA candidate, you should know that OSPF routers use the address 224.0.0.5 to send hellos, EIGRP routers use 224.0.0.10 to send updates, and RIP version 2 uses 224.0.0.9 to send routing updates. RIP version 1 and IGRP both broadcast their updates.
Multicasting gets a bit more complicated as you go from your CCNA to the CCNP and CCIE, but by simply understanding what multicasting is, you go a long way toward securing the CCNA.
A broadcast is simply a unit of information that every other device on the segment will receive. A broadcast is indicated by having every bit of the address set to its highest possible value. Since a hexadecimal bit's highest value is "f", a hexadecimal broadcast is ff-ff-ff-ff-ff-ff (or FF-FF-FF-FF-FF-FF, as the upper case does not affect hex value). The CCNA exam will demand you be very familiar with hex conversions, so if you're not comfortable with these conversions, get comfortable with them before taking the exam!
At layer 3, a broadcast is indicated by setting every bit in the 32-bit binary string to "1", making the dotted decimal value 255.255.255.255. Every host on a segment will receive such a broadcast. (Keep in mind that switches will forward a broadcast, but routers do not.) In contrast to a broadcast, a unicast is a packet or frame with only one destination.
There is a middle ground between broadcasts and unicasts, and that is a multicast. Where a broadcast will be received by all, and a unicast is received by only one host, a multicast will be received by multiple hosts, all belonging to a "multicast group". As you climb the Cisco certification pyramid, you'll be introduced to creating multicast groups and controlling multicast traffic, but for your CCNA studies you need only keep certain multicast groups in mind.
Class D addresses are reserved for multicasting this range is 224.0.0.0 - 239.255.255.255. The addresses 224.0.0.0 - 224.255.255.255 are reserved for use by network protocols on a local network segment, and like broadcasts, routers will not forward these multicast packets. (Packets with these addresses are sent with a Time To Live of 1.)
As a CCNA candidate, you should know that OSPF routers use the address 224.0.0.5 to send hellos, EIGRP routers use 224.0.0.10 to send updates, and RIP version 2 uses 224.0.0.9 to send routing updates. RIP version 1 and IGRP both broadcast their updates.
Multicasting gets a bit more complicated as you go from your CCNA to the CCNP and CCIE, but by simply understanding what multicasting is, you go a long way toward securing the CCNA.
Tuesday, December 23, 2008
Cisco CCNA / CCNP Certification Exam Review: Protocol Basics
To earn your Cisco CCNA certification and pass the BSCI CCNP exam, you have to know your protocol basics like the back of your hand! To help you review these important concepts, here's a quick look at the basics of RIPv1, RIPv2, IGRP, and EIGRP.
RIPv1: Broadcasts updates every 30 seconds to the address 255.255.255.255. RIPv1 is a classful protocol, and it does not recognize VLSM, nor does it carry subnet masking information in its routing updates. Update contains entire RIP routing table. Uses Bellman-Ford algorithm. Allows equal-cost load-balancing by default. Max hop count is 15. Does not support clear-text or MD5 authentication of routing updates. Updates carry 25 routes maximum.
RIPv2: Multicasts updates every 30 seconds to the address 224.0.0.9. RIPv2 is a classless protocol, allowing the use of subnet masks. Update contains entire RIP routing table. Uses Bellman-Ford algorithm. Allows equal-cost load-balancing by default. Max hop count is 15. Supports clear-text and MD5 authentication of routing updates. Updates carry 25 routes maximum.
IGRP: Broadcasts updates every 90 seconds to the address 255.255.255.255. IGRP is a Cisco-proprietary protocol, and is also a classful protocol and does not recognize subnet masking. Update contains entire routing table. Uses Bellman-Ford algorithm. Equal-cost load-balancing on by default; unequal-cost load-sharing can be used with the variance command. Max hop count is 100.
EIGRP: Multicasts full routing table only when an adjacency is first formed. Multicasts updates only when there is a change in the network topology, and then only advertises the change. Multicasts to 224.0.0.10 and allows the use of subnet masks. Uses DUAL routing algorithm. Unequal-cost load-sharing available with the variance command.
By mastering the basics of these protocols, you're laying the foundation for success in the exam room and when working on production networks. Pay attention to the details and the payoff is "CCNA" and "CCNP" behind your name!
RIPv1: Broadcasts updates every 30 seconds to the address 255.255.255.255. RIPv1 is a classful protocol, and it does not recognize VLSM, nor does it carry subnet masking information in its routing updates. Update contains entire RIP routing table. Uses Bellman-Ford algorithm. Allows equal-cost load-balancing by default. Max hop count is 15. Does not support clear-text or MD5 authentication of routing updates. Updates carry 25 routes maximum.
RIPv2: Multicasts updates every 30 seconds to the address 224.0.0.9. RIPv2 is a classless protocol, allowing the use of subnet masks. Update contains entire RIP routing table. Uses Bellman-Ford algorithm. Allows equal-cost load-balancing by default. Max hop count is 15. Supports clear-text and MD5 authentication of routing updates. Updates carry 25 routes maximum.
IGRP: Broadcasts updates every 90 seconds to the address 255.255.255.255. IGRP is a Cisco-proprietary protocol, and is also a classful protocol and does not recognize subnet masking. Update contains entire routing table. Uses Bellman-Ford algorithm. Equal-cost load-balancing on by default; unequal-cost load-sharing can be used with the variance command. Max hop count is 100.
EIGRP: Multicasts full routing table only when an adjacency is first formed. Multicasts updates only when there is a change in the network topology, and then only advertises the change. Multicasts to 224.0.0.10 and allows the use of subnet masks. Uses DUAL routing algorithm. Unequal-cost load-sharing available with the variance command.
By mastering the basics of these protocols, you're laying the foundation for success in the exam room and when working on production networks. Pay attention to the details and the payoff is "CCNA" and "CCNP" behind your name!
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