EIGRP/OSPF LAB: The Merger

In this update I will explore how to merge an existing OSPF network with an existing EIGRP network and also touch on some other subjects which you can read about in the objectives below.

Scenario:

Company A has bought Company B and must merge its network into its own. Company A runs the EIGRP routing protocol and Company B runs the OSPF routing protocol. The engineer will also need to take several other objectives into account such as route summarization, redistribution and the actual connection between the two companies over a leased line.

This lab comes with different objectives that we’ll have to research and try to complete.

Topology:

Preliminary configuration:

  1. Configure all interfaces and the Frame Relay connection.
  2. Configure all Loopback interfaces on each router.
  3. Configure EIGRP AS 10 for Company A.
  4. Configure OSPF 10 for Company B.
  5. Configure OSPF router ID’s for Company B.

Objectives:

  1. Before starting, verify proper operations for each network with the use of a Tcl script.
  2. Summarize the loopback networks on R2 as efficient as possible.
  3. Investigate and implement authentication between R3 & R4.
  4. Redistribute OSPF routes into the EIGRP network.
Instead of going step by step through the preliminary configuration, I will just give you an overview of each router and its base configuration.
If you’d like to know how to configure Frame Relay, base EIGRP or OSPF settings, please refer to my previous updates.

Now that is done, we can get started on our objectives.

Objective one; verify proper operations for each network with the use of a Tcl script.

I will use TCL scripting to check if each configured IP address is reachable for each router.
I have prepared the Tcl script for both companies’ networks in notepad as you can see below. This will then be easy to paste into each router’s cli to test inter-connectivity.

Interestingly enough, after the running the script I saw that everything was reachable, except for R3 and R4 Se 0/0 interface, and this only from its own network or locally on the router itself.

I did some research and it seems that on a connection like this, even when pinging its own local interface, the ping address will still transverse the serial link, which is weird if you ask me!

This can be solved by adding a frame-relay map pointing to the router’s own serial interface IP address. After adding this (and advertising the 10.1.1.3/27 on R3) , the Tcl script was showing full connectivity across the grid for Company A.

Now let’s take a look at Company B. I’ve made the same mistake with the frame relay map on R4, so let’s fix that first.

And now to run the Company B script that I prepared.

Seems like everything is working as should so let’s move on to objective #2; Summarize the loopback networks on R2 as efficient as possible.
I explained how to do manual summarization in this update, so you can click that link if you’re interested in learning how to do this. For now I’ll just calculate the best summary and configure it. Here is how it will end up looking for R2:

On to Objective #3, authentication between R3 and R4.
This is kind of a vague objective, what kind of authentication do they want? I’ll just decide for myself and go with route authentication, also because we will have to set up an OSPF relationship between R3 and R4 anyway for the route redistribution in Objective #4 so I will do both objectives in one go.

First I’ve set up an OSPF relationship between R3 and R4. You can also see that R3 is now aware of the OSPF routes of Company B.

And now we can configure OSPF redistribution into our EIGRP network on R3 with the router process command “redistribute OSPF 10“. You should also set the default-metric with the command “default-metric 10000 100 255 1 1500” or your routes will not be redistributed properly.

We will need to also configure R4’s equivalent and redistribute the EIGRP routes into the OSPF or else they will not be able to communicate. You would need to set up an EIGRP relationship between R4 and R3, and then use the command “redistribute EIGRP 10” under R4’s OSPF router process.

We can test proper functioning by checking the routing table and general reachability with the Company B Tcl script on R2.

Routing Table:
Note how you can see the External (EX) routes showing up now.

And let’s test reachability to Company B’s network from R2 with the prepared script.

Great, that seems to work aswell. Now I just need to configure authentication.
OSPF Authentication is implemented with the router OSPF command “area 1 authentication message-digest” and the interface Serial 0/0 command “ip ospf message-digest-key 1 md5 myospfkey” on both R 3 and R4.

You can verify proper operation of this authentication by seeing that the neighbor relationships come back up after setting the key on both sides.

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