Answers: RIPv2 Basics 2
Once you have read through the book’s material for RIPv2, it should only take two or three good RIP labs to get comfortable with RIP configuration. This latest lab should help you with that bit of practice. You know the drill: check the lab post, then at least write your opinion of the correct configuration on paper, before checking the answer listed here.
For this lab, your job is to take a working IPv4 network that has no routing protocol yet and add the RIPv2 configuration. As usual, check out the lab requirements here and take your shot at the configuration. Then check your answers here vs. my suggested answer.
Answers
Figure 1: Four Router Topology
Example 1: R1 Config
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router rip version 2 no auto-summary network 192.168.1.0 network 192.168.100.0 |
Example 2: R2 Config
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router rip version 2 no auto-summary network 192.168.2.0 network 192.168.100.0 |
Example 3: R3 Config
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router rip version 2 no auto-summary network 192.168.3.0 network 192.168.100.0 ! |
Example 4: R4 Config
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router rip version 2 no auto-summary network 192.168.4.0 network 192.168.100.0 |
Commentary
Two fundamental duties of any network engineer will involve the configuration of IP addresses on routers and the configuration of a routing protocol. RIP is one of the simplest routing protocols to understand which is why it is often taught to new network engineers.
For this lab you were tasked with configuring RIP to ensure that each of the routers had reachability to all of these subnets in a simple design.
The requirements can be broken down into two broad categories: the commands used to enable RIP on router interfaces (using the network command), and any other commands related to RIP.
Covering the related commands first, one requirement stated that the routers should use RIP Version 2 and RIP Version 2 only. To do that, simply configure each RIP process with the version 2 command while inside router configuration mode.
Second, the requirements also asked that you prevent automatic route summarization. That can only happen on routers that has (at least) two interfaces whose IPv4 addresses are from different classful networks. As it turns out, in this design, all four routers have two interfaces that connect to different class C networks. To avoid those summary routes, all four routers need the no auto-summary command in RIP configuration mode to meet the requirements.
Finally, to enable RIP on the correct router interfaces, use the network network command. IOS compares the network parameter to the interface IP addresses configured on a router. With RIP (regardless of version) the network that is configured matches a whole classful network and cannot be limited by a subnet mask or wildcard mask (as with other routing protocols). In this case, all four routers connect to network 192.168.1.0, so all four routers need a network 192.168.100.0 RIP subcommand. Each of the four routers then also connects to one other class C network, requiring one more network command each:
- R1: network 192.168.1.0
- R2: network 192.168.2.0
- R3: network 192.168.3.0
- R4: network 192.168.4.0
Note that if you used extra network commands compared to those in the above list, RIPv2 would work. However, you should work to understand why other network commands on each router would not be needed. For instance, only R1 needs a network 192.168.1.0 command, because only R1 connects to a subnet of class C network 192.168.1.0.
I did the exercise but was unsure about one point.
I understood that the “no auto-summary” should be used when more than one classful network is used, but in this topology, since all of the “subnets” are actually complete classful networks, wouldn’t an auto-summarization end up giving the same result (same networks) as the no auto-summarized routes? Like, a classful summarization for 192.168.1.0/24 is 192.168.1.0/24, right?
In this case, the command would be unnecessary, as the third requirement stated.
Hi Vitor,
I agree with your analysis from a practical perspective. With all class C addresses, and using only default masks of 255.255.255.0, the use of the auto-summary or no auto-summary setting has no effect. I included the “no auto-summary” command just because the lab explicitly asked stated “do not automatically summarize…”. But it would have been more meaningful then if I had just used a /25 mask for instance on all the LAN interfaces, which would have made the “no auto-summary” command necessary.
I did the same thing, and I agree with you
Wendell,
Why wouldn’t the “passive-interface” command be added for each router? Each router has one interface needing no update information.
Hi George,
I agree that “passive-interface” would have use here. However, the lab post asked to use no commands that were not required per the lab, and I’d say that the passive-interface commands are not required. (Stating that kind of requirement is just a way to reduce the variety of “correct” answers so the flow works better in the blog, by the way.)
Wendell
I think I’m a little kerfuffled by the switch with the 192.168.100.0/24 address. The problem states its an L2 switch, and I thought that an IP would only be for remote access purposes… so why does this affect the routers and RIP? Is this switch keeping an IP routing table?
Marisa,
Sorry. That “192.168.100.0/24” is meant to represent the subnet ID and subnet mask of the entire subnet, and is no associated with the switch specifically. Then, each device in the subnet that has an IP address that matters – the 4 routers in this case – show the last octet of their IPv4 addresses in the figure as well.
Your thinking about the L2 switch not needing an IP address for the functions discussed in this post is 100% correct.