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.

EIGRP LAB # 1 : Manual Summarization and Default Network Advertisement

In this lab I will practice manual summarization for EIGRP and also touch on configuring Default Network Advertisement. As you can see from the topology below, we are dealing with quite a few networks that will be the cause for an inefficient routing table.

The idea is to have all these networks summarized in as few routing entries as possible while still maintaining the same functionality.

Lab Topology:

The Loopback Interface on R1 represents an internet connection.
The Loopback interfaces on R2 and R3 represent remote networks.

Objectives:

  1. Configure a Basic EIGRP configuration.
  2. Configure and review EIGRP manual summarization.
  3. Configure Default Network Advertisement.
Let’s start with the first Objective. “Configure a Basic EIGRP configuration“. I will not go through the entire base configuration step by step, you can check my previous updates for that if needed. Instead, here’s the configuration for all three routers that we are starting out with.

R1
==

interface Loopback0
ip address 172.31.1.1 255.255.255.0

interface FastEthernet0/0
ip address 192.168.100.1 255.255.255.248
duplex auto
speed auto

router eigrp 10
network 172.31.0.0
network 192.168.100.0
no auto-summary

R2
==

interface Loopback1
ip address 192.168.200.1 255.255.255.252

interface Loopback5
ip address 192.168.200.5 255.255.255.252

interface Loopback9
ip address 192.168.200.9 255.255.255.252

interface Loopback13
ip address 192.168.200.13 255.255.255.252

interface Loopback17
ip address 192.168.200.17 255.255.255.252

interface Loopback21
ip address 192.168.200.21 255.255.255.252

interface Loopback25
ip address 192.168.200.25 255.255.255.252

interface FastEthernet0/0
ip address 192.168.100.2 255.255.255.248
duplex auto
speed auto

interface FastEthernet0/1
ip address 10.1.1.2 255.255.255.248
duplex auto
speed auto

router eigrp 10
network 10.0.0.0
network 192.168.100.0
network 192.168.200.0
no auto-summary

R3
==

interface Loopback1
ip address 192.168.1.1 255.255.254.0

interface Loopback5
ip address 192.168.5.5 255.255.254.0

interface Loopback9
ip address 192.168.9.9 255.255.254.0

interface Loopback13
ip address 192.168.13.13 255.255.254.0

interface Loopback17
ip address 192.168.17.17 255.255.254.0

interface Loopback21
ip address 192.168.21.21 255.255.254.0

interface Loopback25
ip address 192.168.25.25 255.255.254.0

interface Loopback100
ip address 10.1.3.1 255.255.255.252

interface Loopback172
ip address 172.16.1.1 255.255.255.0

interface FastEthernet0/0
no ip address
shutdown
duplex auto
speed auto

interface FastEthernet0/1
ip address 10.1.1.3 255.255.255.248
duplex auto
speed auto

router eigrp 10
network 10.0.0.0
network 172.16.0.0
network 192.168.0.0 0.0.31.255
no auto-summary

The first big difference from OSPF is that the “autonomous system” number must match on all routers that are to become neighbors with each other.
The “AN” number is configured with the global config command “Router EIGRP 10

I have also disabled auto-summarization for EIGRP with the router config command “no auto-summary“.
EIGRP, like RIP, will summarize at the class-full boundary. Meaning that if you have a route for 10.1.3.0/24 , being a class A address, it will end up being advertised as 10.0.0.0/8
Disabling auto-summary will make it advertise as the classless network 10.1.3.0/24.

Some more explanation on EIGRP.

EIGRP stores its data in three tables.

  1. Neighbor Table: Stores data about the neighboring routers, i.e. those directly accessible through directly connected interfaces
  2. Topology Table: This table contains the aggregation of the routing tables gathered from all directly connected neighbors. For every destination, a successor and a feasible successor are identified and stored in the table if they exist. Every destination in the topology table can be marked either as “Passive“, which is the state when the routing has stabilized and the router knows the route to the destination, or “Active” when the topology has changed and the router is in the process of (actively) updating its route to that destination.
  3. Routing table: Stores the actual routes to all destinations; the routing table is populated from the topology table with every destination network that has its successor and optionally feasible successor identified (if unequal-cost load-balancing is enabled using the variance command). The successors and feasible successors serve as the next hop routers for these destinations.

Now my base configuration is done, we will confirm EIGRP’s proper configuration with the command “show ip eigrp neighbours“.
Here is the output from R2.

R2#show ip eigrp neighbors
IP-EIGRP neighbors for process 10
H Address Interface Hold Uptime SRTT RTO Q Seq
(sec) (ms) Cnt Num
1 10.1.1.3 Fa0/1 10 01:53:10 48 288 0 3
0 192.168.100.1 Fa0/0 13 02:13:11 377 2262 0 9

In this output we can see that, for EIGRP AS 10, it has formed neighbor relationships with the devices connected on Fa0/0 and Fa0/1.
Another interesting command is “show ip eigrp topology” which shows you the network topology as learned from the device’s neighbours.

R2#sh ip eigrp topology
IP-EIGRP Topology Table for AS(10)/ID(192.168.200.25)

Codes: P – Passive, A – Active, U – Update, Q – Query, R – Reply,
r – reply Status, s – sia Status

P 10.1.3.0/30, 1 successors, FD is 409600
via 10.1.1.3 (409600/128256), FastEthernet0/1
P 10.1.1.0/29, 1 successors, FD is 281600
via Connected, FastEthernet0/1
P 192.168.100.0/29, 1 successors, FD is 281600
via Connected, FastEthernet0/0
P 192.168.8.0/23, 1 successors, FD is 409600
via 10.1.1.3 (409600/128256), FastEthernet0/1
P 192.168.12.0/23, 1 successors, FD is 409600
via 10.1.1.3 (409600/128256), FastEthernet0/1
P 192.168.0.0/23, 1 successors, FD is 409600
via 10.1.1.3 (409600/128256), FastEthernet0/1
P 192.168.4.0/23, 1 successors, FD is 409600
via 10.1.1.3 (409600/128256), FastEthernet0/1
P 192.168.24.0/23, 1 successors, FD is 409600
via 10.1.1.3 (409600/128256), FastEthernet0/1
P 192.168.16.0/23, 1 successors, FD is 409600
via 10.1.1.3 (409600/128256), FastEthernet0/1
P 192.168.20.0/23, 1 successors, FD is 409600
via 10.1.1.3 (409600/128256), FastEthernet0/1
P 192.168.200.0/30, 1 successors, FD is 128256
via Connected, Loopback1
P 192.168.200.4/30, 1 successors, FD is 128256
via Connected, Loopback5
P 192.168.200.8/30, 1 successors, FD is 128256
via Connected, Loopback9
P 192.168.200.12/30, 1 successors, FD is 128256
via Connected, Loopback13
P 192.168.200.16/30, 1 successors, FD is 128256
via Connected, Loopback17
P 172.31.1.0/24, 1 successors, FD is 409600
via 192.168.100.1 (409600/128256), FastEthernet0/0
P 192.168.200.20/30, 1 successors, FD is 128256
via Connected, Loopback21
P 192.168.200.24/30, 1 successors, FD is 128256
via Connected, Loopback25
P 172.16.1.0/24, 1 successors, FD is 409600
via 10.1.1.3 (409600/128256), FastEthernet0/1

Okay, before I start trying to summarize all those routes for objective # 2, here’s the output of all three router’s routing tables for later reference and comparison.

R1#sh ip route

Gateway of last resort is not set

172.16.0.0/24 is subnetted, 1 subnets
D 172.16.1.0 [90/435200] via 192.168.100.2, 02:03:31, FastEthernet0/0
172.31.0.0/24 is subnetted, 1 subnets
C 172.31.1.0 is directly connected, Loopback0
192.168.200.0/30 is subnetted, 7 subnets
D 192.168.200.0 [90/409600] via 192.168.100.2, 02:23:31, FastEthernet0/0
D 192.168.200.4 [90/409600] via 192.168.100.2, 02:23:31, FastEthernet0/0
D 192.168.200.8 [90/409600] via 192.168.100.2, 02:23:31, FastEthernet0/0
D 192.168.200.12
[90/409600] via 192.168.100.2, 02:23:32, FastEthernet0/0
D 192.168.200.16
[90/409600] via 192.168.100.2, 02:23:32, FastEthernet0/0
D 192.168.200.20
[90/409600] via 192.168.100.2, 02:23:32, FastEthernet0/0
D 192.168.200.24
[90/409600] via 192.168.100.2, 02:23:33, FastEthernet0/0
10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
D 10.1.3.0/30 [90/435200] via 192.168.100.2, 02:03:34, FastEthernet0/0
D 10.1.1.0/29 [90/307200] via 192.168.100.2, 02:03:51, FastEthernet0/0
192.168.100.0/29 is subnetted, 1 subnets
C 192.168.100.0 is directly connected, FastEthernet0/0
D 192.168.12.0/23 [90/435200] via 192.168.100.2, 02:03:34, FastEthernet0/0
D 192.168.8.0/23 [90/435200] via 192.168.100.2, 02:03:34, FastEthernet0/0
D 192.168.24.0/23 [90/435200] via 192.168.100.2, 02:03:34, FastEthernet0/0
D 192.168.4.0/23 [90/435200] via 192.168.100.2, 02:03:34, FastEthernet0/0
D 192.168.20.0/23 [90/435200] via 192.168.100.2, 02:03:34, FastEthernet0/0
D 192.168.0.0/23 [90/435200] via 192.168.100.2, 02:03:34, FastEthernet0/0
D 192.168.16.0/23 [90/435200] via 192.168.100.2, 02:03:35, FastEthernet0/0
R2#sh ip route

Gateway of last resort is not set

172.16.0.0/24 is subnetted, 1 subnets
D 172.16.1.0 [90/409600] via 10.1.1.3, 02:02:44, FastEthernet0/1
172.31.0.0/24 is subnetted, 1 subnets
D 172.31.1.0 [90/409600] via 192.168.100.1, 02:21:12, FastEthernet0/0
192.168.200.0/30 is subnetted, 7 subnets
C 192.168.200.0 is directly connected, Loopback1
C 192.168.200.4 is directly connected, Loopback5
C 192.168.200.8 is directly connected, Loopback9
C 192.168.200.12 is directly connected, Loopback13
C 192.168.200.16 is directly connected, Loopback17
C 192.168.200.20 is directly connected, Loopback21
C 192.168.200.24 is directly connected, Loopback25
10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
D 10.1.3.0/30 [90/409600] via 10.1.1.3, 02:02:47, FastEthernet0/1
C 10.1.1.0/29 is directly connected, FastEthernet0/1
192.168.100.0/29 is subnetted, 1 subnets
C 192.168.100.0 is directly connected, FastEthernet0/0
D 192.168.12.0/23 [90/409600] via 10.1.1.3, 02:02:47, FastEthernet0/1
D 192.168.8.0/23 [90/409600] via 10.1.1.3, 02:02:47, FastEthernet0/1
D 192.168.24.0/23 [90/409600] via 10.1.1.3, 02:02:47, FastEthernet0/1
D 192.168.4.0/23 [90/409600] via 10.1.1.3, 02:02:47, FastEthernet0/1
D 192.168.20.0/23 [90/409600] via 10.1.1.3, 02:02:47, FastEthernet0/1
D 192.168.0.0/23 [90/409600] via 10.1.1.3, 02:02:47, FastEthernet0/1
D 192.168.16.0/23 [90/409600] via 10.1.1.3, 02:02:47, FastEthernet0/1
R3#sh ip route

Gateway of last resort is not set

172.16.0.0/24 is subnetted, 1 subnets
C 172.16.1.0 is directly connected, Loopback172
172.31.0.0/24 is subnetted, 1 subnets
D 172.31.1.0 [90/435200] via 10.1.1.2, 02:04:18, FastEthernet0/1
192.168.200.0/30 is subnetted, 7 subnets
D 192.168.200.0 [90/409600] via 10.1.1.2, 02:04:18, FastEthernet0/1
D 192.168.200.4 [90/409600] via 10.1.1.2, 02:04:18, FastEthernet0/1
D 192.168.200.8 [90/409600] via 10.1.1.2, 02:04:18, FastEthernet0/1
D 192.168.200.12 [90/409600] via 10.1.1.2, 02:04:19, FastEthernet0/1
D 192.168.200.16 [90/409600] via 10.1.1.2, 02:04:19, FastEthernet0/1
D 192.168.200.20 [90/409600] via 10.1.1.2, 02:04:19, FastEthernet0/1
D 192.168.200.24 [90/409600] via 10.1.1.2, 02:04:19, FastEthernet0/1
10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C 10.1.3.0/30 is directly connected, Loopback100
C 10.1.1.0/29 is directly connected, FastEthernet0/1
192.168.100.0/29 is subnetted, 1 subnets
D 192.168.100.0 [90/307200] via 10.1.1.2, 02:04:20, FastEthernet0/1
C 192.168.12.0/23 is directly connected, Loopback13
C 192.168.8.0/23 is directly connected, Loopback9
C 192.168.24.0/23 is directly connected, Loopback25
C 192.168.4.0/23 is directly connected, Loopback5
C 192.168.20.0/23 is directly connected, Loopback21
C 192.168.0.0/23 is directly connected, Loopback1
C 192.168.16.0/23 is directly connected, Loopback17

Now let’s get summarizing. I will first make an overview for the loopbacks per router so I know which addresses are available.
Then after that I will look what can be done with the remaining addresses.

Okay, first up, R2. It looks like we have a range from 192.168.200.1 to 192.168.200.25.
To find out which mask we can use to summarize these routes with, we have to check which increment to use that will encompass everything from 1 to 25.

Draw the following chart.

128   64   32   16   8   4   2   1

Now check which number is big enough to hold everything from 1 to 25.
That would be 32 right? So draw the following.

128   64   32   16   8   4   2   1

1        1      1     0   0   0   0   0

Now consider the IP address we’re working with. We know nothing changes in the first three octets right? So we can be sure our subnet mask will look like 255.255.255.x where “x” is the number we’re looking for. Using the method from above, this means we’ll need to add 3 bits to our subnet mask.
( 3 x 8 1‘s + 3 1’s ).
This will give us a subnet mask of 255.255.255.224 or /27 in CIDR notation.

We now end up with the subnet 192.168.200.0/27 which has the host range from 192.168.200.1 to 192.168.200.30
Using the same calculation, we end up with 192.168.0.0/19 for R3.

Now to configure our manual summarization. This can be done with the interface command “ip summary-address eigrp 10 address mask” and should be configured on the interface where you want the summarization to happen.

Let’s do it.

R2(config)#int fa 0/0
R2(config-if)#ip summary-address eigrp 10 192.168.200.0 255.255.255.224
R2(config-if)#int fa 0/1
R2(config-if)#ip summary-address eigrp 10 192.168.200.0 255.255.255.224I’ve configured summarization on those interfaces and looks what happens:

*Mar 1 04:05:11.926: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 10.1.1.3 (FastEthernet0/1) is resync: summary configured

*Mar 1 04:06:47.706: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 10: Neighbor 10.1.1.3 (FastEthernet0/1) is resync: peer graceful-restart

Our router notices what we are up to and gracefully reinitializes the neighbourship so its neighbours can learn of the new route.
Let’s do the same for R3.

R3(config)#int fa 0/1
R3(config-if)#ip summary-address eigrp 10 192.168.0.0 255.255.224.0

Okay, let’s take a look now at our new and improved routing table.

R1#sh ip route

Gateway of last resort is not set

172.16.0.0/24 is subnetted, 1 subnets
D 172.16.1.0 [90/435200] via 192.168.100.2, 00:10:13, FastEthernet0/0
172.31.0.0/24 is subnetted, 1 subnets
C 172.31.1.0 is directly connected, Loopback0
192.168.200.0/27 is subnetted, 1 subnets
D 192.168.200.0 [90/409600] via 192.168.100.2, 00:10:13, FastEthernet0/0
10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
D 10.1.3.0/30 [90/435200] via 192.168.100.2, 00:10:13, FastEthernet0/0
D 10.1.1.0/29 [90/307200] via 192.168.100.2, 00:10:14, FastEthernet0/0
192.168.100.0/29 is subnetted, 1 subnets
C 192.168.100.0 is directly connected, FastEthernet0/0
D 192.168.0.0/19 [90/435200] via 192.168.100.2, 00:06:21, FastEthernet0/0

Much much cleaner. But can we still ping all our loopbacks? Did I even do this right?
Oh god, let’s quickly test.

R1#traceroute 192.168.200.13

Type escape sequence to abort.
Tracing the route to 192.168.200.13

1 192.168.100.2 32 msec * 28 msec
R1#
R1#traceroute 192.168.1.1

Type escape sequence to abort.
Tracing the route to 192.168.1.1

1 192.168.100.2 52 msec 20 msec 20 msec
2 10.1.1.3 40 msec * 40 msec

Victory! You don’t see it here, but I tried reaching every loopback address and they all worked.

We still have the other addresses to check, but I plan to update this entry later on with that information.

For now, let’s do objective #3, Configure Default Network Advertisement.

This can be done with the command “IP Default-network address” which should be configured on R1.

R1(config)#ip default-network 172.31.0.0

R1 will then automatically advertise its new default route.
And the routing table on R2 says ..

R2#sh ip route eigrp
172.16.0.0/24 is subnetted, 1 subnets
D 172.16.1.0 [90/409600] via 10.1.1.3, 00:25:54, FastEthernet0/1
* 172.31.0.0/24 is subnetted, 1 subnets
D 172.31.1.0 [90/409600] via 192.168.100.1, 00:03:10, FastEthernet0/0
192.168.200.0/24 is variably subnetted, 8 subnets, 2 masks
D 192.168.200.0/27 is a summary, 00:26:27, Null0
10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
D 10.1.3.0/30 [90/409600] via 10.1.1.3, 00:25:54, FastEthernet0/1
D 192.168.0.0/19 [90/409600] via 10.1.1.3, 00:22:01, FastEthernet0/1

There’s our default route, the one with the *, indicating it’s a “candidate default”

And that’s a wrap!

Note to self: Come back and check the 10. and 172. routes! 
This lab has been based on chapter 2-3 of the Cisco CCNP Route LAB Manual.
Other references:
cbtnuggets.com
Enhanced Interior Gateway Routing Protocol.