Wednesday, 5 October 2016

Route redistribution with OSPF and EIGRP

Route redistribution is simply the process of sharing information between two or more routing protocols - since by design OSPF and EIGRP (RIP etc.) are not compatible with each other - for example ODPF uses cost as a metric, while EIGRP uses K-Values.

For this lab we will be redistributing routing information across a EIGRP and OSPF domain - we will be using the previous lab here as a starting point.



With the addition of a EIGRP domain of which we want to redistribute information accross the OSPF and EIGRP domain:

R2>
int e0/1
ip address 172.16.30.1 255.255.255.252
no shutdown
ip ospf 1 area 0

router ospf 1
network 172.16.30.0 0.0.0.3 area 0


R3>
enable
conf t
int e0/1
ip address 10.1.0.1 255.255.255.252
no shutdown

int e0/0
ip address 172.16.30.2 255.255.255.252
no shutdown
ip ospf 1 area 0

we will create a new EIGRP AS:

router eigrp 10
no auto-summary
network 10.1.0.0 0.0.0.3

router ospf 1
router-id 3.3.3.3
network 172.16.30.0 0.0.0.3 area 0

R4>
enable
conf t
int e0/0
ip address 10.1.0.2 255.255.255.252
no shutdown

int e0/1
ip address 10.16.32.1 255.255.255.0
no shutdown

router eigrp 10
no auto-summary
network 10.1.0.0 0.0.0.3
network 10.16.32.0 0.0.0.255

We should now see a new adjacency form - confirm with:

do show ip eigrp ne

Now we need to perform the redistribution - one important thing to remember about route redistribution is that it is an outbound process for example in our topology

Since different routing protocols use different metrics we will need to convert the metric from one protocol to one that supports the destination routiong protocol - for example:

Redistribution into RIP requires the seed metric of 'Infinity.'
Redistribution into EIGRP requires the seed metric of 'Infinity.'
Redistribution into OSPF requires the seed metric of '20' or '1' if originating from BGP.
Redistribution into BGP requires the IGP metric.

Because we want to distribute our routes into our EIGRP domain we also need to ensure we have set our default K-Values as the routes will not show up without this information firstly defined:

R3>
router eigrp 10
default-metric 1500 100 255 1 1500
redistribute ospf 1 metric 1544 2000 255 1 1500

and then the other way  - redistributing OSPF routes into EIGRP:
router ospf 1
redistribute eigrp 10 metric 50000 subnets

We can then hop onto R2 and check the routes - you will notice something like the following:

O E2    10.1.0.0/30 [110/50000] via 172.16.30.2, 00:02:19, Ethernet0/1
O E2    10.16.32.0/24 [110/50000] via 172.16.30.2, 00:02:19, Ethernet0/1

Note: The E2 indicates that the network is resides outside the OSPF domain - that is - within our EIGRP domain.

And again on R4 we should see something like:

D EX    172.16.30.0 [170/2195456] via 10.1.0.1, 00:05:07, Ethernet0/0
     10.0.0.0/8 is variably subnetted, 3 subnets, 2 masks
D EX    10.0.0.0/30 [170/2195456] via 10.1.0.1, 00:05:07, Ethernet0/0

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