To pass the BCMSN exam and earn your CCNP, you've got to know HSRP inside and out! Part of that is knowing how the MAC address of the virtual router is derived, and another part is knowing how to change this address. We'll look at both features in this tutorial.
We've got two routers on a segment running HSRP, so first we need to find out what the MAC address of the HSRP virtual router is. The show command for HSRP is show standby, and it's the first command you should run while configuring and troubleshooting HSRP. Let's run it on both routers and compare results.
R2#show standby
Ethernet0 - Group 5
Local state is Standby, priority 100
Hellotime 3 sec, holdtime 10 sec
Next hello sent in 0.776
Virtual IP address is 172.12.23.10 configured
Active router is 172.12.23.3, priority 100 expires in 9.568
Standby router is local
1 state changes, last state change 00:00:22
R3#show standby
Ethernet0 - Group 5
Local state is Active, priority 100
Hellotime 3 sec, holdtime 10 sec
Next hello sent in 2.592
Virtual IP address is 172.12.23.10 configured
Active router is local
Standby router is 172.12.23.2 expires in 8.020
Virtual mac address is 0000.0c07.ac05
2 state changes, last state change 00:02:08
R3 is in Active state, while R2 is in Standby. The hosts are using the 172.12.123.10 address as their gateway, but R3 is actually handling the workload. R2 will take over if R3 becomes unavailable.
An IP address was statically assigned to the virtual router, but not a MAC address. However, there is a MAC address under the show standby output on R3, the active router. How did the HSRP process arrive at a MAC of 00-00-0c-07-ac-05?
Well, most of the work is already done before the configuration is even begun. The MAC address 00-00-0c-07-ac-xx is reserved for HSRP, and xx is the group number in hexadecimal. That's a good skill to have for the exam, so make sure you're comfortable with hex conversions. The group number is 5, which is expressed as 05 with a two-bit hex character. If the group number had been 17, we'd see 11 at the end of the MAC address - one unit of 16, one unit of 1.
On rare occasions, you may have to change the MAC address assigned to the virtual router. This is done with the standby mac-address command. Just make sure you're not duplicating a MAC address that's already on your network!
R2(config-if)#standby 5 mac-address 0000.1111.2222
1d12h: %STANDBY-6-STATECHANGE: Ethernet0 Group 5 state Active -> Learn
R2#show standby
Ethernet0 - Group 5
Local state is Active, priority 150, may preempt
Hellotime 4 sec, holdtime 12 sec
Next hello sent in 3.476
Virtual IP address is 172.12.23.10 configured
Active router is local
Standby router is 172.12.23.3 expires in 10.204
Virtual mac address is 0000.1111.2222 configured
4 state changes, last state change 00:00:00
1d12h: %STANDBY-6-STATECHANGE: Ethernet0 Group 5 state Listen -> Active
The MAC address will take a few seconds to change, and the HSRP routers will go into Learn state for that time period.
A real-world HSRP troubleshooting note: If you see constant state changes with your HSRP configuration, do what you should always do when troubleshooting - check the physical layer first. Best of luck on your BCMSN exam!
Showing posts with label address. Show all posts
Showing posts with label address. Show all posts
Thursday, December 25, 2008
Cisco CCNP / BSCI Exam Tutorial: Route Summarization
Preparing to pass the BSCI exam and earn your Cisco CCNP? Route summarization is just one of the many skills you'll have to master in order to earn your CCNP. Whether it's RIP version 2, OSPF, or EIGRP, the BSCI exam will demand that you can flawlessly configure route summarization.
Route summarization isn't just important for the BSCI exam. It's a valuable skill to have in the real world as well. Correctly summarizing routes can lead to smaller routing tables that are still able to route packets accurately - what I like to call "concise and complete" routing tables.
The first skill you've got to have in order to work with route summarization is binary math more specifically, you must be able to take multiple routes and come up with both a summary route and mask to advertise to downstream routers. Given the networks 100.16.0.0 /16, 100.17.0.0 /16, 100.18.0.0 /16, and 100.19.0.0 /16, could you quickly come up with both the summary address and mask? All you need to do is break the four network numbers down into binary strings. We know the last two octets will all convert to the binary string 00000000, so in this article we'll only illustrate how to convert the first and second octet from decimal to binary.
100 16 = 01100100 00010000
100 17 = 01100100 00010001
100 18 = 01100100 00010010
100 19 = 01100100 00010011
To come up with the summary route, just work from left to right and draw a line where the four networks no longer have a bit in common. For these four networks, that point comes between the 14th and 15th bits. This leaves us with this string: 01100100 000100xx. All you need to do is convert that string back to decimal, which gives us 100 for the first octet and 16 for the second. (The two x values are bits on the right side of the line, which aren't used in calculating the summary route.) Since we know that zero is the value for the last two octets, the resulting summary network number is 100.16.0.0.
But we're not done! We now have to come up with the summary mask to advertise along with the summary route. To arrive at the summary route, write out a mask in binary with a "1" for every bit to the left of the line we drew previously, and a "0" for every bit to the right. That gives us the following string:
11111111 11111100 00000000 00000000
Converting that to dotted decimal, we arrive at the summary mask 255.252.0.0. The correct summary network and mask to advertise are 100.16.0.0 252.0.0.0.
For the BSCI exam, emphasis is put on knowing how to advertise these summary routes in RIPv2, EIGRP, and OSPF. For RIP v2 and EIGRP, route summarization happens at the interface level - it's not configured under the protocol. On the interface that should advertise the summary route, use the command "ip summary-address". Here are examples of how the above summary route would be configured on ethernet0 in both RIPv2 and EIGRP.
R1(config-if)#ip summary-address rip 100.16.0.0 255.252.0.0
R1(config-if)#ip summary-address eigrp 100 100.16.0.0 255.252.0.0
The main difference between the two is that the EIGRP command must specify the AS number - that's what the "100" is in the middle of the EIGRP command. Since RIPv2 does not use AS numbers, there's no additional value needed in the configuration.
For OSPF, the commands differ. If you're configuring inter-area route summarization, use the "area range" command. The number following "area" is the area containing the routes being summarized, not the area receiving the summary.
R1(config)#router ospf 1
R1(config-router)#area 1 range 100.16.0.0 255.252.0.0
If you are summarizing routes that are being redistributed into OSPF, use the summary-address command under the OSPF routing process on the ASBR.
R1(config)#router ospf 1
R1(config-router)#summary-address 100.16.0.0 255.252.0.0
I speak from experience when I tell you that practice makes perfect on the BSCI exam, especially with binary and summarization questions. The great thing about these questions is that there are no grey areas with these questions - you either know how to do it or you don't. And with practice and an eye for detail, you can master these skills, pass the exam, and become a CCNP. Here's to your success on these tough Cisco certification exams!
Route summarization isn't just important for the BSCI exam. It's a valuable skill to have in the real world as well. Correctly summarizing routes can lead to smaller routing tables that are still able to route packets accurately - what I like to call "concise and complete" routing tables.
The first skill you've got to have in order to work with route summarization is binary math more specifically, you must be able to take multiple routes and come up with both a summary route and mask to advertise to downstream routers. Given the networks 100.16.0.0 /16, 100.17.0.0 /16, 100.18.0.0 /16, and 100.19.0.0 /16, could you quickly come up with both the summary address and mask? All you need to do is break the four network numbers down into binary strings. We know the last two octets will all convert to the binary string 00000000, so in this article we'll only illustrate how to convert the first and second octet from decimal to binary.
100 16 = 01100100 00010000
100 17 = 01100100 00010001
100 18 = 01100100 00010010
100 19 = 01100100 00010011
To come up with the summary route, just work from left to right and draw a line where the four networks no longer have a bit in common. For these four networks, that point comes between the 14th and 15th bits. This leaves us with this string: 01100100 000100xx. All you need to do is convert that string back to decimal, which gives us 100 for the first octet and 16 for the second. (The two x values are bits on the right side of the line, which aren't used in calculating the summary route.) Since we know that zero is the value for the last two octets, the resulting summary network number is 100.16.0.0.
But we're not done! We now have to come up with the summary mask to advertise along with the summary route. To arrive at the summary route, write out a mask in binary with a "1" for every bit to the left of the line we drew previously, and a "0" for every bit to the right. That gives us the following string:
11111111 11111100 00000000 00000000
Converting that to dotted decimal, we arrive at the summary mask 255.252.0.0. The correct summary network and mask to advertise are 100.16.0.0 252.0.0.0.
For the BSCI exam, emphasis is put on knowing how to advertise these summary routes in RIPv2, EIGRP, and OSPF. For RIP v2 and EIGRP, route summarization happens at the interface level - it's not configured under the protocol. On the interface that should advertise the summary route, use the command "ip summary-address". Here are examples of how the above summary route would be configured on ethernet0 in both RIPv2 and EIGRP.
R1(config-if)#ip summary-address rip 100.16.0.0 255.252.0.0
R1(config-if)#ip summary-address eigrp 100 100.16.0.0 255.252.0.0
The main difference between the two is that the EIGRP command must specify the AS number - that's what the "100" is in the middle of the EIGRP command. Since RIPv2 does not use AS numbers, there's no additional value needed in the configuration.
For OSPF, the commands differ. If you're configuring inter-area route summarization, use the "area range" command. The number following "area" is the area containing the routes being summarized, not the area receiving the summary.
R1(config)#router ospf 1
R1(config-router)#area 1 range 100.16.0.0 255.252.0.0
If you are summarizing routes that are being redistributed into OSPF, use the summary-address command under the OSPF routing process on the ASBR.
R1(config)#router ospf 1
R1(config-router)#summary-address 100.16.0.0 255.252.0.0
I speak from experience when I tell you that practice makes perfect on the BSCI exam, especially with binary and summarization questions. The great thing about these questions is that there are no grey areas with these questions - you either know how to do it or you don't. And with practice and an eye for detail, you can master these skills, pass the exam, and become a CCNP. Here's to your success on these tough Cisco certification exams!
Cisco CCNP / BSCI Exam Tutorial: Using The OSPF Command “Area Range”
Your BSCI and CCNP exam success depends on knowing the details, and one such detail is knowing the proper way to summarize routes in OSPF. Route summarization is not just a test of your binary conversion abilities, but knowing where and when to summarize routes. It will not surprise any CCNA or CCNP certification candidate that OSPF gives us the most options for route summarization, and therefore more details to know!
OSPF offers us two options for route summarization configurations. In a previous tutorial, we looked at the "summary-address" command, and today we'll look at the proper use of the "area range" command.
The "area range" command should be used on an Area Border Router (ABR) to summarize routes being advertised from one OSPF area to another. In this tutorial, R1 is acting as an ABR, with interfaces in both Area 0 and Area 1. Four loopbacks have been placed into R1's Area 1.
R1(config)#router ospf 1
R1(config-router)#network 12.0.0.0 0.255.255.255 a 1
R1(config-router)#network 13.0.0.0 0.255.255.255 a 1
R1(config-router)#network 14.0.0.0 0.255.255.255 a 1
R1(config-router)#network 15.0.0.0 0.255.255.255 a 1
The routing table of an OSPF neighbor, R2, shows all four routes.
R2#show ip route ospf
12.0.0.0/32 is subnetted, 1 subnets
O IA 12.12.12.12 [110/65] via 172.12.123.1, 00:18:52, Serial0
13.0.0.0/32 is subnetted, 1 subnets
O IA 13.13.13.13 [110/65] via 172.12.123.1, 00:18:42, Serial0
14.0.0.0/32 is subnetted, 1 subnets
O IA 14.14.14.14 [110/65] via 172.12.123.1, 00:18:32, Serial0
15.0.0.0/32 is subnetted, 1 subnets
O IA 15.15.15.15 [110/65] via 172.12.123.1, 00:18:32, Serial0
To keep the routing tables of downstream routers smaller but still have the desired IP connectivity, we can use the area range command on R1 to summarize these four routes. The key to keep in mind with the area range command is that the area number given in the command is the area containing the destinations, NOT the area that will receive the summary route.
R1(config)#router ospf 1
R1(config-router)#area 1 range 12.0.0.0 252.0.0.0
R2 now shows a single summary route that can be used to reach all four remote networks.
R2#show ip route ospf
O IA 12.0.0.0/6 [110/65] via 172.12.123.1, 00:00:21, Serial0
Interestingly enough, there's now an additional route in R1's routing table.
R1#show ip route ospf
O 12.0.0.0/6 is a summary, 00:07:53, Null0
When you configure summary routes in OSPF, a route to null0 will be installed into the OSPF routing table of the router performing the summarization. This helps to prevent routing loops. Any packets destined for the routes that have been summarized will have a longer match in the routing table, and packets that do not match one of the summarized routes but do match the summary route will be dropped.
OSPF offers us two options for route summarization configurations. In a previous tutorial, we looked at the "summary-address" command, and today we'll look at the proper use of the "area range" command.
The "area range" command should be used on an Area Border Router (ABR) to summarize routes being advertised from one OSPF area to another. In this tutorial, R1 is acting as an ABR, with interfaces in both Area 0 and Area 1. Four loopbacks have been placed into R1's Area 1.
R1(config)#router ospf 1
R1(config-router)#network 12.0.0.0 0.255.255.255 a 1
R1(config-router)#network 13.0.0.0 0.255.255.255 a 1
R1(config-router)#network 14.0.0.0 0.255.255.255 a 1
R1(config-router)#network 15.0.0.0 0.255.255.255 a 1
The routing table of an OSPF neighbor, R2, shows all four routes.
R2#show ip route ospf
12.0.0.0/32 is subnetted, 1 subnets
O IA 12.12.12.12 [110/65] via 172.12.123.1, 00:18:52, Serial0
13.0.0.0/32 is subnetted, 1 subnets
O IA 13.13.13.13 [110/65] via 172.12.123.1, 00:18:42, Serial0
14.0.0.0/32 is subnetted, 1 subnets
O IA 14.14.14.14 [110/65] via 172.12.123.1, 00:18:32, Serial0
15.0.0.0/32 is subnetted, 1 subnets
O IA 15.15.15.15 [110/65] via 172.12.123.1, 00:18:32, Serial0
To keep the routing tables of downstream routers smaller but still have the desired IP connectivity, we can use the area range command on R1 to summarize these four routes. The key to keep in mind with the area range command is that the area number given in the command is the area containing the destinations, NOT the area that will receive the summary route.
R1(config)#router ospf 1
R1(config-router)#area 1 range 12.0.0.0 252.0.0.0
R2 now shows a single summary route that can be used to reach all four remote networks.
R2#show ip route ospf
O IA 12.0.0.0/6 [110/65] via 172.12.123.1, 00:00:21, Serial0
Interestingly enough, there's now an additional route in R1's routing table.
R1#show ip route ospf
O 12.0.0.0/6 is a summary, 00:07:53, Null0
When you configure summary routes in OSPF, a route to null0 will be installed into the OSPF routing table of the router performing the summarization. This helps to prevent routing loops. Any packets destined for the routes that have been summarized will have a longer match in the routing table, and packets that do not match one of the summarized routes but do match the summary route will be dropped.
Cisco CCNP / BSCI Exam Tutorial: Using OSPF's "Summary-Address" Command
BSCI exam success, not to mention earning your CCNP, can come down to your OSPF route summarization skills. There are a few different commands and situations you need to be ready for, and one of these situations is the proper use of the "summary-address" command.
The summary-address command should be used on an ASBR in order to summarize routes that are being injected into the OSPF domain via redistribution. In the following example, four routes are being redisitributed into OSPF on R1, making R1 an ASBR.
interface Loopback16
ip address 16.16.16.16 255.0.0.0
!
interface Loopback17
ip address 17.17.17.17 255.0.0.0
!
interface Loopback18
ip address 18.18.18.18 255.0.0.0
!
interface Loopback19
ip address 19.19.19.19 255.0.0.0
R1(config)#router ospf 1
R1(config-router)#redistribute connected subnets
These four routes are seen on downstream router R2 as External Type-2, the default for routes redistributed into OSPF.
R2#show ip route ospf
O E2 17.0.0.0/8 [110/20] via 172.12.123.1, 00:00:07, Serial0
O E2 16.0.0.0/8 [110/20] via 172.12.123.1, 00:00:07, Serial0
O E2 19.0.0.0/8 [110/20] via 172.12.123.1, 00:00:07, Serial0
O E2 18.0.0.0/8 [110/20] via 172.12.123.1, 00:00:07, Serial0
To summarize networks learned by redistribution, use the OSPF command summary-address. You can probably do this summarization in your head, but do so before continuing with the lab.
R1(config)#router ospf 1
R1(config-router)#summary-address 16.0.0.0 252.0.0.0
Look at the change in R2's OSPF table.
R2#show ip route ospf
O E2 16.0.0.0/6 [110/20] via 172.12.123.1, 00:00:05, Serial0
The external routes have been successfully summarized. Note that the summary route is still marked as an E2 route.
There's an interesting route installed into R1's OSPF table as well.
R1#show ip route ospf
O 16.0.0.0/6 is a summary, 00:01:51, Null0
When you configure summary routes in OSPF, a route to null0 will be installed into the OSPF routing table. This helps to prevent routing loops. Any packets destined for the routes that have been summarized will have a longer match in the routing table....
C 17.0.0.0/8 is directly connected, Loopback17
C 16.0.0.0/8 is directly connected, Loopback16
C 19.0.0.0/8 is directly connected, Loopback19
C 18.0.0.0/8 is directly connected, Loopback18
O 16.0.0.0/6 is a summary, 00:03:10, Null0
O 12.0.0.0/6 is a summary, 00:07:53, Null0
.. and packets that do not match one of the summarized routes but do match the summary route will be dropped.
The summary-address command should be used on an ASBR in order to summarize routes that are being injected into the OSPF domain via redistribution. In the following example, four routes are being redisitributed into OSPF on R1, making R1 an ASBR.
interface Loopback16
ip address 16.16.16.16 255.0.0.0
!
interface Loopback17
ip address 17.17.17.17 255.0.0.0
!
interface Loopback18
ip address 18.18.18.18 255.0.0.0
!
interface Loopback19
ip address 19.19.19.19 255.0.0.0
R1(config)#router ospf 1
R1(config-router)#redistribute connected subnets
These four routes are seen on downstream router R2 as External Type-2, the default for routes redistributed into OSPF.
R2#show ip route ospf
O E2 17.0.0.0/8 [110/20] via 172.12.123.1, 00:00:07, Serial0
O E2 16.0.0.0/8 [110/20] via 172.12.123.1, 00:00:07, Serial0
O E2 19.0.0.0/8 [110/20] via 172.12.123.1, 00:00:07, Serial0
O E2 18.0.0.0/8 [110/20] via 172.12.123.1, 00:00:07, Serial0
To summarize networks learned by redistribution, use the OSPF command summary-address. You can probably do this summarization in your head, but do so before continuing with the lab.
R1(config)#router ospf 1
R1(config-router)#summary-address 16.0.0.0 252.0.0.0
Look at the change in R2's OSPF table.
R2#show ip route ospf
O E2 16.0.0.0/6 [110/20] via 172.12.123.1, 00:00:05, Serial0
The external routes have been successfully summarized. Note that the summary route is still marked as an E2 route.
There's an interesting route installed into R1's OSPF table as well.
R1#show ip route ospf
O 16.0.0.0/6 is a summary, 00:01:51, Null0
When you configure summary routes in OSPF, a route to null0 will be installed into the OSPF routing table. This helps to prevent routing loops. Any packets destined for the routes that have been summarized will have a longer match in the routing table....
C 17.0.0.0/8 is directly connected, Loopback17
C 16.0.0.0/8 is directly connected, Loopback16
C 19.0.0.0/8 is directly connected, Loopback19
C 18.0.0.0/8 is directly connected, Loopback18
O 16.0.0.0/6 is a summary, 00:03:10, Null0
O 12.0.0.0/6 is a summary, 00:07:53, Null0
.. and packets that do not match one of the summarized routes but do match the summary route will be dropped.
Cisco CCNP / BSCI Exam Tutorial: IP Version 6 Zero Compression
BSCI exam success is all part of becoming a CCNP, and part of that success is now learning the basics of IP Version 6, or IPv6. One of the most difficult parts of learning IPv6 concepts is the radically different addressing scheme that IPv6 uses as compared to IPv4. Just look at these sample addresses:
Typical IPv4 address: 129.14.12.200
Typical IPv6 address: 1029:9183:81AE:0000:0000:0AC1:2143:019B
As you can see, IPv6 isn't exactly just tacking two more octets onto an IPv4 address!
I haven't met too many networkers who really like typing, particularly numbers. You'll be happy to know there are some rules that will shorten those addresses a bit, and it's a very good idea to be fluent with these rules for your exam.
You remember from your CCNA studies that there's no difference between an upper-case letter and lower-case letter in hexadecimal. That's one of three basic rules you need to know when working with IPv6 addressing. The other factors deal with all the zeroes you'll run into in IPv6 addresses! One of these rules is the rule of zero compression.
The rule of zero compression states that if an address contains consecutive fields of zeroes, they can be expressed with two colons. It doesn't matter if you have two fields or eight, you can simply type two colons and that will represent all of them. The key here is that you can only do this once in an IPv6 address. This is referred to as zero compression. Here's an example:
Original format: 1234:1234:0000:0000:0000:0000:3456:3434
Using zero compression: 1234:1234::3456:3434
Again, you must remember that you can only do this once in an IPv6 address expression.
What if there are zeroes in the address that don't quite fit this rule? The next part of our IPv6 tutorial will deal with leading zero compression, another tool you can use to shorten these long, long addresses!
Typical IPv4 address: 129.14.12.200
Typical IPv6 address: 1029:9183:81AE:0000:0000:0AC1:2143:019B
As you can see, IPv6 isn't exactly just tacking two more octets onto an IPv4 address!
I haven't met too many networkers who really like typing, particularly numbers. You'll be happy to know there are some rules that will shorten those addresses a bit, and it's a very good idea to be fluent with these rules for your exam.
You remember from your CCNA studies that there's no difference between an upper-case letter and lower-case letter in hexadecimal. That's one of three basic rules you need to know when working with IPv6 addressing. The other factors deal with all the zeroes you'll run into in IPv6 addresses! One of these rules is the rule of zero compression.
The rule of zero compression states that if an address contains consecutive fields of zeroes, they can be expressed with two colons. It doesn't matter if you have two fields or eight, you can simply type two colons and that will represent all of them. The key here is that you can only do this once in an IPv6 address. This is referred to as zero compression. Here's an example:
Original format: 1234:1234:0000:0000:0000:0000:3456:3434
Using zero compression: 1234:1234::3456:3434
Again, you must remember that you can only do this once in an IPv6 address expression.
What if there are zeroes in the address that don't quite fit this rule? The next part of our IPv6 tutorial will deal with leading zero compression, another tool you can use to shorten these long, long addresses!
Cisco CCNP / BSCI Exam Tutorial: EIGRP Route Summarization
Summarizing routes is a vital skill to learn to pass the BSCI exam and get one step closer to earning your CCNP. The actual binary conversions are only part of the test, though! You've got to know how to correctly apply the summary routes, and that differs from one protocol to the next. In the last few CCNP / BSCI tutorials, we've looked at using the "area range" and "summary-address" commands to perform OSPF route summarization. Today, we'll take a look at summarizing routes in EIGRP.
We'll use the following four loopback addresses in this example:
Loopback 16, 16.16.16.16 /32
Loopback 17, 17.17.17.17 /32
Loopback 18, 18.18.18.18 /32
Loopback 19. 19.19.19.19 /32
On R1, we'll place these four addresses into EIGRP AS 100.
R1(config-if)#router eigrp 100
R1(config-router)#network 16.16.16.16 0.0.0.0
R1(config-router)#network 17.17.17.17 0.0.0.0
R1(config-router)#network 18.18.18.18 0.0.0.0
R1(config-router)#network 19.19.19.19 0.0.0.0
R3 is an EIGRP neighbor of R1, and that router's EIGRP routing table now looks like this:
R3#show ip route eigrp
17.0.0.0/32 is subnetted, 1 subnets
D 17.17.17.17 [90/2297856] via 172.12.123.1, 00:00:29, Serial0
16.0.0.0/32 is subnetted, 1 subnets
D 16.16.16.16 [90/2297856] via 172.12.123.1, 00:00:36, Serial0
19.0.0.0/32 is subnetted, 1 subnets
D 19.19.19.19 [90/2297856] via 172.12.123.1, 00:00:08, Serial0
18.0.0.0/32 is subnetted, 1 subnets
D 18.18.18.18 [90/2297856] via 172.12.123.1, 00:00:22, Serial0
To perform manual route summarization, write out the network addresses in binary and then determine the point at which the addresses no longer have a bit in common. For these four addresses, it will be enough to write out the first octet in binary:
16 00010000
17 00010001
18 00010010
19 00010011
Working from left to right, the common bits are the first six bits - 000100xx. In decimal, this value is 16. The summary mask must be determined as well, and that value is derived from putting a "1" in the mask for each common bit. With the first six bits all set to one - 11111100 - the resulting mask is 252.0.0.0. The full summary address is 16.0.0.0 252.0.0.0.
In EIGRP, the summary address is actually configured on an interface, not under the routing process.
R1(config)#interface serial0
R1(config-if)#ip summary-address eigrp 100 16.0.0.0 252.0.0.0
02:39:50: %DUAL-5-NBRCHANGE: IP-EIGRP 100: Neighbor
172.12.123.3 (Serial0) is down: summary configured
02:39:50: %DUAL-5-NBRCHANGE: IP-EIGRP 100: Neighbor
172.12.123.2 (Serial0) is down: summary configured
02:40:16: %DUAL-5-NBRCHANGE: IP-EIGRP 100: Neighbor
172.12.123.2 (Serial0) is up : new adjacency
02:40:17: %DUAL-5-NBRCHANGE: IP-EIGRP 100: Neighbor
172.12.123.3 (Serial0) is up: new adjacency
There's an immediate side effect here that most books leave out. Your EIGRP adjacencies are going to come down after you configure this summary, but they should come back up quickly. The key word there is "should". If you configure EIGRP summary addresses on a production network, you may want to do this during non-peak hours. The timestamps on the above commands indicate that the adjacencies were down for about 27 seconds over the NBMA network. That's about 30 minutes in end-user time. ;)
Check R3's EIGRP routing table.
R3#show ip route eigrp
D 16.0.0.0/6 [90/2297856] via 172.12.123.1, 00:01:46, Serial0
The four summarized routes are no longer in the routing table, and they have been replaced by the summary route shown at the bottom of the routing table. Notice the mask is /5, which is prefix notation for 248.0.0.0.
Knowing how and why to summarize routes is a valuable skill, regardless of the protocol in use. But before you take the BSCI exam on your way to the CCNP, make sure you know how to perform summarization with all of the core protocols!
We'll use the following four loopback addresses in this example:
Loopback 16, 16.16.16.16 /32
Loopback 17, 17.17.17.17 /32
Loopback 18, 18.18.18.18 /32
Loopback 19. 19.19.19.19 /32
On R1, we'll place these four addresses into EIGRP AS 100.
R1(config-if)#router eigrp 100
R1(config-router)#network 16.16.16.16 0.0.0.0
R1(config-router)#network 17.17.17.17 0.0.0.0
R1(config-router)#network 18.18.18.18 0.0.0.0
R1(config-router)#network 19.19.19.19 0.0.0.0
R3 is an EIGRP neighbor of R1, and that router's EIGRP routing table now looks like this:
R3#show ip route eigrp
17.0.0.0/32 is subnetted, 1 subnets
D 17.17.17.17 [90/2297856] via 172.12.123.1, 00:00:29, Serial0
16.0.0.0/32 is subnetted, 1 subnets
D 16.16.16.16 [90/2297856] via 172.12.123.1, 00:00:36, Serial0
19.0.0.0/32 is subnetted, 1 subnets
D 19.19.19.19 [90/2297856] via 172.12.123.1, 00:00:08, Serial0
18.0.0.0/32 is subnetted, 1 subnets
D 18.18.18.18 [90/2297856] via 172.12.123.1, 00:00:22, Serial0
To perform manual route summarization, write out the network addresses in binary and then determine the point at which the addresses no longer have a bit in common. For these four addresses, it will be enough to write out the first octet in binary:
16 00010000
17 00010001
18 00010010
19 00010011
Working from left to right, the common bits are the first six bits - 000100xx. In decimal, this value is 16. The summary mask must be determined as well, and that value is derived from putting a "1" in the mask for each common bit. With the first six bits all set to one - 11111100 - the resulting mask is 252.0.0.0. The full summary address is 16.0.0.0 252.0.0.0.
In EIGRP, the summary address is actually configured on an interface, not under the routing process.
R1(config)#interface serial0
R1(config-if)#ip summary-address eigrp 100 16.0.0.0 252.0.0.0
02:39:50: %DUAL-5-NBRCHANGE: IP-EIGRP 100: Neighbor
172.12.123.3 (Serial0) is down: summary configured
02:39:50: %DUAL-5-NBRCHANGE: IP-EIGRP 100: Neighbor
172.12.123.2 (Serial0) is down: summary configured
02:40:16: %DUAL-5-NBRCHANGE: IP-EIGRP 100: Neighbor
172.12.123.2 (Serial0) is up : new adjacency
02:40:17: %DUAL-5-NBRCHANGE: IP-EIGRP 100: Neighbor
172.12.123.3 (Serial0) is up: new adjacency
There's an immediate side effect here that most books leave out. Your EIGRP adjacencies are going to come down after you configure this summary, but they should come back up quickly. The key word there is "should". If you configure EIGRP summary addresses on a production network, you may want to do this during non-peak hours. The timestamps on the above commands indicate that the adjacencies were down for about 27 seconds over the NBMA network. That's about 30 minutes in end-user time. ;)
Check R3's EIGRP routing table.
R3#show ip route eigrp
D 16.0.0.0/6 [90/2297856] via 172.12.123.1, 00:01:46, Serial0
The four summarized routes are no longer in the routing table, and they have been replaced by the summary route shown at the bottom of the routing table. Notice the mask is /5, which is prefix notation for 248.0.0.0.
Knowing how and why to summarize routes is a valuable skill, regardless of the protocol in use. But before you take the BSCI exam on your way to the CCNP, make sure you know how to perform summarization with all of the core protocols!
Cisco CCNP / BSCI Exam Tutorial: A Guide To Ipv6 Addressing
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.
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.
Cisco CCNP / BCSI Exam Tutorial: Broadcasts And The IP Helper-Address Command
While routers accept and generate broadcasts, they do not forward them. This can be quite a problem when a broadcast needs to get to a device such as a DHCP or TFTP server that's on one side of a router with other subnets on the other side.
If a PC attempts to locate a DNS server with a broadcast, the broadcast will be stopped by the router and will never get to the DNS server. By configuring the ip helper-address command on the router, UDP broadcasts such as this will be translated into a unicast by the router, making the communication possible. The command should be configured on the interface that will be receiving the broadcasts.
R1(config)#int e0
R1(config-if)#ip helper-address ?
A.B.C.D IP destination address
R1(config-if)#ip helper-address 100.1.1.2
Now, you may be wondering if this command covers all UDP services. Sorry, you're not getting off that easy! The command does forward eight common UDP service broadcasts, though.
TIME, port 37
TACACS, port 49
DNS, port 53
BOOTP/DHCP Server, port 67
BOOTP/DHCP Client, port 68
TFTP, port 69
NetBIOS name service, port 137
NetBIOS datagram service, port 138
That's going to cover most scenarios where the ip helper-address command will be useful, but what about those situations where the broadcast you need forwarded is not on this list? You can use the ip forward-protocol command to add any UDP port number to the list.
Additionally, to remove protocols from the default list, use the no ip forward-protocol command. In the following example, we'll add the Network Time Protocol port to the forwarding list while removing the NetBIOS ports. Remember, you can use IOS Help to get a list of commonly filtered ports!
R1(config)#ip forward-protocol udp ?
<0-65535> Port number
biff Biff (mail notification, comsat, 512)
bootpc Bootstrap Protocol (BOOTP) client (68)
bootps Bootstrap Protocol (BOOTP) server (67)
discard Discard (9)
dnsix DNSIX security protocol auditing (195)
domain Domain Name Service (DNS, 53)
echo Echo (7)
isakmp Internet Security Association and Key Management Protocol (500)
mobile-ip Mobile IP registration (434)
nameserver IEN116 name service (obsolete, 42)
netbios-dgm NetBios datagram service (138)
netbios-ns NetBios name service (137)
netbios-ss NetBios session service (139)
ntp Network Time Protocol (123)
pim-auto-rp PIM Auto-RP (496)
rip Routing Information Protocol (router, in.routed, 520)
snmp Simple Network Management Protocol (161)
snmptrap SNMP Traps (162)
sunrpc Sun Remote Procedure Call (111)
syslog System Logger (514)
tacacs TAC Access Control System (49)
talk Talk (517)
tftp Trivial File Transfer Protocol (69)
time Time (37)
who Who service (rwho, 513)
xdmcp X Display Manager Control Protocol (177)
R1(config)#ip forward-protocol udp 123
R1(config)#no ip forward-protocol udp 137
R1(config)#no ip forward-protocol udp 138
As you can see, the ip helper-address command helps work around the fact that broadcasts aren't forwarded by routers by default, and if you just need to send one or two broadcast types, the other types can be turned off easily.
If a PC attempts to locate a DNS server with a broadcast, the broadcast will be stopped by the router and will never get to the DNS server. By configuring the ip helper-address command on the router, UDP broadcasts such as this will be translated into a unicast by the router, making the communication possible. The command should be configured on the interface that will be receiving the broadcasts.
R1(config)#int e0
R1(config-if)#ip helper-address ?
A.B.C.D IP destination address
R1(config-if)#ip helper-address 100.1.1.2
Now, you may be wondering if this command covers all UDP services. Sorry, you're not getting off that easy! The command does forward eight common UDP service broadcasts, though.
TIME, port 37
TACACS, port 49
DNS, port 53
BOOTP/DHCP Server, port 67
BOOTP/DHCP Client, port 68
TFTP, port 69
NetBIOS name service, port 137
NetBIOS datagram service, port 138
That's going to cover most scenarios where the ip helper-address command will be useful, but what about those situations where the broadcast you need forwarded is not on this list? You can use the ip forward-protocol command to add any UDP port number to the list.
Additionally, to remove protocols from the default list, use the no ip forward-protocol command. In the following example, we'll add the Network Time Protocol port to the forwarding list while removing the NetBIOS ports. Remember, you can use IOS Help to get a list of commonly filtered ports!
R1(config)#ip forward-protocol udp ?
<0-65535> Port number
biff Biff (mail notification, comsat, 512)
bootpc Bootstrap Protocol (BOOTP) client (68)
bootps Bootstrap Protocol (BOOTP) server (67)
discard Discard (9)
dnsix DNSIX security protocol auditing (195)
domain Domain Name Service (DNS, 53)
echo Echo (7)
isakmp Internet Security Association and Key Management Protocol (500)
mobile-ip Mobile IP registration (434)
nameserver IEN116 name service (obsolete, 42)
netbios-dgm NetBios datagram service (138)
netbios-ns NetBios name service (137)
netbios-ss NetBios session service (139)
ntp Network Time Protocol (123)
pim-auto-rp PIM Auto-RP (496)
rip Routing Information Protocol (router, in.routed, 520)
snmp Simple Network Management Protocol (161)
snmptrap SNMP Traps (162)
sunrpc Sun Remote Procedure Call (111)
syslog System Logger (514)
tacacs TAC Access Control System (49)
talk Talk (517)
tftp Trivial File Transfer Protocol (69)
time Time (37)
who Who service (rwho, 513)
xdmcp X Display Manager Control Protocol (177)
R1(config)#ip forward-protocol udp 123
R1(config)#no ip forward-protocol udp 137
R1(config)#no ip forward-protocol udp 138
As you can see, the ip helper-address command helps work around the fact that broadcasts aren't forwarded by routers by default, and if you just need to send one or two broadcast types, the other types can be turned off easily.
Cisco CCNP / BCMSN Exam Tutorial: Dynamic VLANs and VMPS
Knowledge of Dynamic VLANs and VMPS is important in your efforts to pass the BCMSN exam and earn your CCNP, and it's also a great skill to have for your networking career.
As a CCNA and CCNP candidate, you know how and why to configure static VLANs. Static VLANs can be a powerful tool for reducing unnecessary broadcast and multicast traffic, but if hosts are moved from one switch port to another, you've got to make those changes manually on the switch. With Dynamic VLANs, the changes are made - how else? - dynamically.
The actual configuration of dynamic VLANs is out of the scope of the BCMSN exam, but as a CCNP candidate you need to know the basics of VMPS - a VLAN Membership Policy Server.
Using VMPS results in port VLAN membership changes being performed dynamically, because the port's VLAN membership is decided by the source MAC address of the device connected to that port. (Yet another reason that the first value a switch looks at on an incoming frame is the source MAC address.)
In my home lab network, I've got a host connected to switch port fast0/1 that resides in VLAN 12. What if we had to move Host 1's connection to the switch to port 0/6? With static VLANs, we'd have to connect to the switch, configure the port as an access port, and then place the port into VLAN 12. With VMPS, the only thing we'd have to do is reconnect the cable to port 0/6, and the VMPS would dynamically place that port into VLAN 12.
I urge you to do additional reading regarding VMPS. Use your favorite search engine for the term configuring vmps and you'll quickly find some great official Cisco documentation on this topic.
To review, the VLAN membership of a host is decided by one of two factors. With static VLANs, the host's VLAN membership is the VLAN to which its switch port has been assigned. With dynamic VLANs, it is dependent upon the host's MAC address.
As a CCNA and CCNP candidate, you know how and why to configure static VLANs. Static VLANs can be a powerful tool for reducing unnecessary broadcast and multicast traffic, but if hosts are moved from one switch port to another, you've got to make those changes manually on the switch. With Dynamic VLANs, the changes are made - how else? - dynamically.
The actual configuration of dynamic VLANs is out of the scope of the BCMSN exam, but as a CCNP candidate you need to know the basics of VMPS - a VLAN Membership Policy Server.
Using VMPS results in port VLAN membership changes being performed dynamically, because the port's VLAN membership is decided by the source MAC address of the device connected to that port. (Yet another reason that the first value a switch looks at on an incoming frame is the source MAC address.)
In my home lab network, I've got a host connected to switch port fast0/1 that resides in VLAN 12. What if we had to move Host 1's connection to the switch to port 0/6? With static VLANs, we'd have to connect to the switch, configure the port as an access port, and then place the port into VLAN 12. With VMPS, the only thing we'd have to do is reconnect the cable to port 0/6, and the VMPS would dynamically place that port into VLAN 12.
I urge you to do additional reading regarding VMPS. Use your favorite search engine for the term configuring vmps and you'll quickly find some great official Cisco documentation on this topic.
To review, the VLAN membership of a host is decided by one of two factors. With static VLANs, the host's VLAN membership is the VLAN to which its switch port has been assigned. With dynamic VLANs, it is dependent upon the host's MAC address.
Cisco CCNA Exam Tutorial: Route Summarization
Preparing to pass the CCNA exam and earn this important Cisco certification? Route summarization is just one of the many skills you'll have to master in order to earn your CCNA. Whether it's RIP version 2, OSPF, or EIGRP, the CCNA exam will demand that you can flawlessly configure route summarization.
Route summarization isn't just important for the CCNA exam. It's a valuable skill to have in the real world as well. Correctly summarizing routes can lead to smaller routing tables that are still able to route packets accurately - what I like to call "concise and complete" routing tables.
The first skill you've got to have in order to work with route summarization is binary math; more specifically, you must be able to take multiple routes and come up with both a summary route and mask to advertise to downstream routers. Given the networks 100.16.0.0 /16, 100.17.0.0 /16, 100.18.0.0 /16, and 100.19.0.0 /16, could you quickly come up with both the summary address and mask? All you need to do is break the four network numbers down into binary strings. We know the last two octets will all convert to the binary string 00000000, so in this article we'll only illustrate how to convert the first and second octet from decimal to binary.
100 16 = 01100100 00010000
100 17 = 01100100 00010001
100 18 = 01100100 00010010
100 19 = 01100100 00010011
To come up with the summary route, just work from left to right and draw a line where the four networks no longer have a bit in common. For these four networks, that point comes between the 14th and 15th bits. This leaves us with this string: 01100100 000100xx. All you need to do is convert that string back to decimal, which gives us 100 for the first octet and 16 for the second. (The two x values are bits on the right side of the line, which aren't used in calculating the summary route.) Since we know that zero is the value for the last two octets, the resulting summary network number is 100.16.0.0.
But we're not done! We now have to come up with the summary mask to advertise along with the summary route. To arrive at the summary route, write out a mask in binary with a "1" for every bit to the left of the line we drew previously, and a "0" for every bit to the right. That gives us the following string:
11111111 11111100 00000000 00000000
Converting that to dotted decimal, we arrive at the summary mask 255.252.0.0. The correct summary network and mask to advertise are 100.16.0.0 252.0.0.0.
For the CCNA exam, emphasis is put on knowing how to advertise these summary routes in RIPv2 and EIGRP. For both of these protocols, route summarization happens at the interface level - it's not configured under the protocol. On the interface that should advertise the summary route, use the command "ip summary-address". Here are examples of how the above summary route would be configured on ethernet0 in both RIPv2 and EIGRP.
R1(config-if)#ip summary-address rip 100.16.0.0 255.252.0.0
R1(config-if)#ip summary-address eigrp 100 100.16.0.0 255.252.0.0
The main difference between the two is that the EIGRP command must specify the AS number - that's what the "100" is in the middle of the EIGRP command. Since RIPv2 does not use AS numbers, there's no additional value needed in the configuration.
For OSPF, the commands differ. If you're configuring inter-area route summarization, use the "area range" command; if you are summarizing routes that are being redistributed into OSPF, use the summary-address command under the OSPF routing process on the ASBR. Neither of these are interface-level commands.
I speak from experience when I tell you that practice makes perfect on the CCNA exam, especially with binary and summarization questions. The great thing about these questions is that there are no grey areas with these questions - you either know how to do it or you don't. And with practice and an eye for detail, you can master these skills, pass the exam, and become a CCNA. Here's to your success!
Route summarization isn't just important for the CCNA exam. It's a valuable skill to have in the real world as well. Correctly summarizing routes can lead to smaller routing tables that are still able to route packets accurately - what I like to call "concise and complete" routing tables.
The first skill you've got to have in order to work with route summarization is binary math; more specifically, you must be able to take multiple routes and come up with both a summary route and mask to advertise to downstream routers. Given the networks 100.16.0.0 /16, 100.17.0.0 /16, 100.18.0.0 /16, and 100.19.0.0 /16, could you quickly come up with both the summary address and mask? All you need to do is break the four network numbers down into binary strings. We know the last two octets will all convert to the binary string 00000000, so in this article we'll only illustrate how to convert the first and second octet from decimal to binary.
100 16 = 01100100 00010000
100 17 = 01100100 00010001
100 18 = 01100100 00010010
100 19 = 01100100 00010011
To come up with the summary route, just work from left to right and draw a line where the four networks no longer have a bit in common. For these four networks, that point comes between the 14th and 15th bits. This leaves us with this string: 01100100 000100xx. All you need to do is convert that string back to decimal, which gives us 100 for the first octet and 16 for the second. (The two x values are bits on the right side of the line, which aren't used in calculating the summary route.) Since we know that zero is the value for the last two octets, the resulting summary network number is 100.16.0.0.
But we're not done! We now have to come up with the summary mask to advertise along with the summary route. To arrive at the summary route, write out a mask in binary with a "1" for every bit to the left of the line we drew previously, and a "0" for every bit to the right. That gives us the following string:
11111111 11111100 00000000 00000000
Converting that to dotted decimal, we arrive at the summary mask 255.252.0.0. The correct summary network and mask to advertise are 100.16.0.0 252.0.0.0.
For the CCNA exam, emphasis is put on knowing how to advertise these summary routes in RIPv2 and EIGRP. For both of these protocols, route summarization happens at the interface level - it's not configured under the protocol. On the interface that should advertise the summary route, use the command "ip summary-address". Here are examples of how the above summary route would be configured on ethernet0 in both RIPv2 and EIGRP.
R1(config-if)#ip summary-address rip 100.16.0.0 255.252.0.0
R1(config-if)#ip summary-address eigrp 100 100.16.0.0 255.252.0.0
The main difference between the two is that the EIGRP command must specify the AS number - that's what the "100" is in the middle of the EIGRP command. Since RIPv2 does not use AS numbers, there's no additional value needed in the configuration.
For OSPF, the commands differ. If you're configuring inter-area route summarization, use the "area range" command; if you are summarizing routes that are being redistributed into OSPF, use the summary-address command under the OSPF routing process on the ASBR. Neither of these are interface-level commands.
I speak from experience when I tell you that practice makes perfect on the CCNA exam, especially with binary and summarization questions. The great thing about these questions is that there are no grey areas with these questions - you either know how to do it or you don't. And with practice and an eye for detail, you can master these skills, pass the exam, and become a CCNA. Here's to your success!
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!
Monday, December 22, 2008
CCNP Certification / BCMSN Exam Tutorial: HSRP MAC Addresses And Timers
To earn your CCNP certification and pass the BCMSN exam, you've got to know what HSRP does and the many configurable options. While the operation of HSRP is quite simple (and covered in a previous tutorial), you also need to know how HSRP arrives at the MAC address for the virtual router - as well as how to configure a new MAC for this virtual router. This puts us in the unusual position of creating a physical address for a router that doesn't exist!
The output of show standby for a two-router HSRP configuration is shown below.
R2#show standby
Ethernet0 - Group 5
Local state is Standby, priority 100
Hellotime 3 sec, holdtime 10 sec
Next hello sent in 0.776
Virtual IP address is 172.12.23.10 configured
Active router is 172.12.23.3, priority 100 expires in 9.568
Standby router is local
1 state changes, last state change 00:00:22
R3#show standby
Ethernet0 - Group 5
Local state is Active, priority 100
Hellotime 3 sec, holdtime 10 sec
Next hello sent in 2.592
Virtual IP address is 172.12.23.10 configured
Active router is local
Standby router is 172.12.23.2 expires in 8.020
Virtual mac address is 0000.0c07.ac05
2 state changes, last state change 00:02:08
R3 is in Active state, while R2 is in Standby. The hosts are using the 172.12.123.10 address as their gateway, but R3 is actually handling the workload. R2 will take over if R3 becomes unavailable.
An IP address was assigned to the virtual router during the HSRP configuration process, but not a MAC address. However, there is a MAC address under the show standby output on R3, the active router. How did the HSRP process arrive at a MAC of 00-00-0c-07-ac-05?
Well, most of the work is already done before the configuration is even begun. The MAC address 00-00-0c-07-ac-xx is reserved for HSRP, and xx is the group number in hexadecimal. That's a good skill to have for the exam, so make sure you're comfortable with hex conversions. The group number is 5, which is expressed as 05 with a two-bit hex character. If the group number had been 17, we'd see 11 at the end of the MAC address - one unit of 16, one unit of 1.
The output of the show standby command also tells us that the HSRP speakers are sending Hellos every 3 seconds, with a 10-second holdtime. These values can be changed with the standby command, but HSRP speakers in the same group should have the same timers. You can even tie down the hello time to the millisecond, but it's doubtful you'll ever need to do that.
R3(config-if)#standby 5 timers ?
<1-254> Hello interval in seconds
msec Specify hello interval in milliseconds
R3(config-if)#standby 5 timers 4 ?
<5-255> Hold time in seconds
R3(config-if)#standby 5 timers 4 12
Another important HSRP skill is knowing how to change the Active router assignment. I'll show you how to do that, and how to configure HSRP interface tracking, in the next part of my CCNP / BCMSN exam tutorial!
The output of show standby for a two-router HSRP configuration is shown below.
R2#show standby
Ethernet0 - Group 5
Local state is Standby, priority 100
Hellotime 3 sec, holdtime 10 sec
Next hello sent in 0.776
Virtual IP address is 172.12.23.10 configured
Active router is 172.12.23.3, priority 100 expires in 9.568
Standby router is local
1 state changes, last state change 00:00:22
R3#show standby
Ethernet0 - Group 5
Local state is Active, priority 100
Hellotime 3 sec, holdtime 10 sec
Next hello sent in 2.592
Virtual IP address is 172.12.23.10 configured
Active router is local
Standby router is 172.12.23.2 expires in 8.020
Virtual mac address is 0000.0c07.ac05
2 state changes, last state change 00:02:08
R3 is in Active state, while R2 is in Standby. The hosts are using the 172.12.123.10 address as their gateway, but R3 is actually handling the workload. R2 will take over if R3 becomes unavailable.
An IP address was assigned to the virtual router during the HSRP configuration process, but not a MAC address. However, there is a MAC address under the show standby output on R3, the active router. How did the HSRP process arrive at a MAC of 00-00-0c-07-ac-05?
Well, most of the work is already done before the configuration is even begun. The MAC address 00-00-0c-07-ac-xx is reserved for HSRP, and xx is the group number in hexadecimal. That's a good skill to have for the exam, so make sure you're comfortable with hex conversions. The group number is 5, which is expressed as 05 with a two-bit hex character. If the group number had been 17, we'd see 11 at the end of the MAC address - one unit of 16, one unit of 1.
The output of the show standby command also tells us that the HSRP speakers are sending Hellos every 3 seconds, with a 10-second holdtime. These values can be changed with the standby command, but HSRP speakers in the same group should have the same timers. You can even tie down the hello time to the millisecond, but it's doubtful you'll ever need to do that.
R3(config-if)#standby 5 timers ?
<1-254> Hello interval in seconds
msec Specify hello interval in milliseconds
R3(config-if)#standby 5 timers 4 ?
<5-255> Hold time in seconds
R3(config-if)#standby 5 timers 4 12
Another important HSRP skill is knowing how to change the Active router assignment. I'll show you how to do that, and how to configure HSRP interface tracking, in the next part of my CCNP / BCMSN exam tutorial!
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