Redistribution: More EIGRP Redistribution

EIGRP has a default seed metric of “infinity”, and we need to define a seed metric when we perform the redistribution. With EIGRP, that means defining five different settings.

There are two ways to set the seed metric with EIGRP:

  1. Set the metric for the redistributed routes learned from a specific source at the end of the redistribute command.
  2. Use the default-metric command to set the default metric for all routes being redistributed.

Example:

R3(config-router)#redistribute rip metric 1544 10 255 1 1500
R3(config-router)#redistribute connected metric 1544 10 255 1 1500

Fairly straightforward stuff.

Or using default metric option:

R2(config)#router eigrp 100
R2(config-router)#default-metric 1544 10 255 1 1500

Be very careful when redistributing with RIP as the AD for RIP routes is 120 and will be ‘better’ then External EIGRP routes with an AD of 170. This is example where we may need to change the AD for EIGRP to something lower than 120.

Example:

R2(config)#router eigrp 100
R2(config-router)#distance ?
<1-255> Administrative distance
eigrp IP-EIGRP distance
R2(config-router)#distance eigrp ?
<1-255> Distance for internal routes
R2(config-router)#distance eigrp 90 ?
<1-255> Distance for external routes
R2(config-router)#distance eigrp 90 119

show ip protocols’ is an excellent command for reviewing redistribution.

 

 

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Route Redistribution: Changing the AD

If we have an example whereby we are going to be redistributing between RIP and OSPF, we need to consider the AD.

We know that RIP uses an AD of 120 and OSPF uses 110, we might have an example whereby the best OSPF (selected by the AD) is not in fact the preferred or optimal path to the destination. We can get around this by changing the AD value for OSPF specifically.

To change the AD of a protocol on a router, use the distance command under the appropriate routing process. We’ll use this command to change the AD of OSPF on R2 to 200.

R2(config)#router ospf 1
R2(config-router)#distance ?
<1-255> Administrative distance
ospf OSPF distance
R2(config-router)#distance 121

This is now a higher value than RIP and therefore the RIP route with the AD of 120 will now be the ‘best’ route to the destination.

You can also change the AD for specific routes only!

Example config:

Let’s double the AD of the route for 4.4.4.4 while leaving the other routes alone. ACL 5 identifies that route and that route only, and then we just use that ACL number at the end of the distance command.

R2(config)#access-list 5 permit 4.4.4.4 0.0.0.0
R2(config)#router eigrp 100
R2(config-router)#distance 180 0.0.0.0 255.255.255.255 ?
<1-99> IP Standard access list number
<1300-1999> IP Standard expanded access list number
WORD Standard access-list name
R2(config-router)#distance 180 0.0.0.0 255.255.255.255 5

After clearing the route table, the route to 4.4.4.4 now has an AD of 180, while the other distances remain the same.