Redistribution between Eigrp and BGP to setup a new backup link

[gryffindor]

Hi All

I need help regarding setup of a new backup connection between my DCs. The link is terminated on edge routers in each DC, namely DC1-edge and DC2-edge. There is EIGRP (As 40) running between two edge routers. On DC-1, we have eBGP between DC1-core and DC1-edge and we will have to redistribute the EIGRP 40 routes into this BGP. On DC-2, we have another EIGRP (AS 50) between DC2-core and DC2-edge and will do redistribution between these two.

We have few other eigrp (both AS 40 and 50) neighborships on DC2-edge router. Redistribution is already configured there betwen DC2-edge and DC2-core and I will have to just update the prefix list there advertise the routes to core. But because of existing metric config, core will use this new link as primary and I don't know how to cofigure metric for different routes.

Similary, on DC-1 core we are getting the routes from primary link through another EIGRP (AD value 160) while the AD of routes from the BGP with DC1-edge would be 20. I don't think we can modify BGP AD value for a neighbor there as well. 

I hope, I have make my problem clear (non-native speaker).

Thanks

[Giuseppe Larosa]

Hello @gryffindor ,

>> We have few other eigrp (both AS 40 and 50) neighborships on DC2-edge router. Redistribution is already configured there betwen DC2-edge and DC2-core and I will have to just update the prefix list there advertise the routes to core. But because of existing metric config, core will use this new link as primary and I don't know how to cofigure metric for different routes.

You need to use a second prefix-list to be used to match prefixes coming from the new backup link.

your route-map will need to be configured with multiple clauses / blocks

! existing route map for example:

route-map EIGRP-TO-BGP permit 10

match address prefix PL1

set metric 50

you add

route-map EIGRP-TO-BGP permit 20

match address prefix PL2

set metric 5000

This allows you to set different metric values in redistribution of EIGRP into BGP.

Hope to help

Giuseppe

[gryffindor]

Hi @Giuseppe Larosa 

Thanks a lot for your reply. I wasn't aware of this command. Just to confirm, can I use the same method for redistribuiting eigrp into eigrp (another AS).

Can you please also suggest something for this. 

>> Similary, on DC-1 core we are getting the routes from primary link through another EIGRP (AD value 160) while the AD of routes from the BGP (backup link) with DC1-edge would be 20. I don't think we can modify BGP AD value for a neighbor there as well. 

[Giuseppe Larosa]

Hello @gryffindor ,

BGP has a feature called backdoor that allows to deal with this type of scenario.

on DC-edge device that has the eBGP session on the backup link you need to add

under router bgp <your AS>

network   <prefix> <prefix-mask> backdoor

do it for each prefix you receive on the backup link

This will increase the AD to 200 like it was an iBGP learned path and this should make it less preferred then the EIGRP learned route.

Hope to help

Giuseppe

[MHM Cisco World]

why you run EIGRP between the two Edge router ? if there direct connect then only config iBGP between them and make edge router only advertise to each other the prefix from eBGP.