mpls-bgp-2 isps

Unanswered Question
Sep 20th, 2008
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I have the following scenario, please refer to the attachement.

There are basically 2 links from each site.

Site A - One active link is to ISP1 and the other link is a standby to ISP2.

Site B - One active link is to ISP2 and the other link is a standby to ISP1.

This topology is also replicated at sites C,D.

I am not really sure about the bgp config between the CEs and the PEs.

Any suggestions is very much appreciated.



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Giuseppe Larosa Sun, 09/21/2008 - 01:43
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Hello Paul,

when using two different ISPs two strategies are possible:

a) choice for all sites one ISP as primary and the other one as backup

b) tune the BGP config to use both ISP services

I don't think it is easy to have :

Site A: isp1 primary isp2 secondary

Site B: isp1 secondary isp2 secondary

for this to work this way the two ISPs must cooperate and setup inter-AS VPN, but from a redundancy point of view would be better if the two ISPs offer really separated services.

I would consider to modify this requirements.

Hope to help


Marwan ALshawi Sun, 09/21/2008 - 01:53
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if u use VRFs on the PEs and all sites A,B,C and D in the same VRF/VPN then

the communication between each CE and its connected PE will be any routing protocol depends on the ISP mybe static route, mybe BGP or any IGP

within the provider network the PEs will redistribute this route into MP-BGP VPNv4

and vice versa

for example on PE1

router ospf 2 vrf CUSTA


redistribute bgp 1 subnets

network x.x.x.x y.y.y.y area 0

bgp 1

address-family ipv4 vrf CUSTA

redistribute ospf 2 vrf CUSTA match internal external 1 external 2

no synchronization


if helpful Rate


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