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BGP multihome Failover Question

I have DS3 to main provider

I am getting 2 T1s DIA to fail over to a different provider (don't want to use them unless i have to)

I am already set to bgp peer with DS3 provider, but will need to set up BGP peer with other provider shortly and set it up as failover. I want to advertise to both, but dont' want anything to do with load balance.

Q1) What is the optimal configuration for what i want to do?

here is my best guess for my scenario

__________________________________________________

interface Hssi1

ip address y.y.y.y+1 255.255.255.252

interface serial2

ip adddress a.a.a.a 255.255.255.252

interface serial3

ip address b.b.b.b 255.255.255.252

BGP myASN

network x.x.x.x 255.255.192.0

neighbor y.y.y.yremote-as DS3provider_ASN

neighbor y.y.y.y filter-list 10 out

neighbor y.y.y.y soft-reconfiguration inbound

neighbor y.y.y.y route-map ABC out

neighbor z.z.z.z remote-as 2T1provider_ASN

neighbor z.z.z.z filter-list 10 out

neighbor z.z.z.z soft-reconfiguration inbound

neighbor z.z.z.z route-map ABC out

no auto summary

ip as-path access-list 10 permit ^$

route-map ABC permit 10

match as-path 10

ip route 0.0.0.0 0.0.0.0 y.y.y.y 5

ip route 0.0.0.0 0.0.0.0 z.z.z.z 10

ip route z.z.z.z 255.255.255.252 a.a.a.a

ip route z.z.z.z 255.255.255.252 b.b.b.b

______________________________________________________

Q2) If this works right.. how does the incoming traffic come in as far as choosing where to come in through. They are just going to use whatever is closer/faster? Any way to control that?

Thanx in advance

1 REPLY
Cisco Employee

Re: BGP multihome Failover Question

Hello Ben,

Your configuration will not work. Here is the correct configuraiton:

router bgp

network x.x.x.x 255.255.192.0

neighbor y.y.y.y remotge-as DS3provider_ASN

neighbor y.y.y.y weighth 200 <------This will always prefer this link for all outgoing traffic

neighbor y.y.y.y filter-list 10 out

neighbor y.y.y.y soft-reconfiguration inbound

neighbor z.z.z.z remote-as 2T1provider_ASN

neighbor z.z.z.z filter-list 10 out

neighbor z.z.z.z soft-reconfiguration inbound

!! The following configs below will help in advertising your network with worst path to the outside world. Now there is always a possibility that the outside world may have their outgoing policy that will override this but this configs work in most cases !!

neighbor z.z.z.z route-map asprepend out

ip as-path access-list 10 permit ^$

route-map asprepend

match as-path 10

set as-path prepend

Hope it help,

Faraz

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