Load sharing/balancing between 2 Service Providers

Unanswered Question
Sep 1st, 2008
User Badges:


I have a scenario where I have the following and this is repeated at different sites globally.

CE1-----------PE1_SP1---MPLS cloud


CE1---standby--PE2_SP1---MPLS cloud

CE2-----------PE1_SP2----MPLS Cloud


CE2---standby--PE2_SP2---MPLS Cloud

2 different service providers and we require load sharing/balancing to both SP1 and SP2.

If either of the SP's PE router is down it should bring up the standby link.

2 ASN, not sure if I can load share different prefixes in this scenario.

Will the applications fail?

Will the traffic flow be symmetric ?

Any help is very much appreciated.



  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
Giuseppe Larosa Mon, 09/01/2008 - 12:22
User Badges:
  • Super Silver, 17500 points or more
  • Hall of Fame,

    Founding Member

Hello Paul,

if you are using a single CE router on each site.

to get load-balancing on your CEx:

router bgp X

maximum-paths 2

eBGP load-balancing is easier so 2 ISP ASN is fine

Verify that you have flow based load-balancing and everything should be fine.

Notice that you have a failure on site N of provider1 you can be able to detect it in all remote sites only if they are receiving the routes of all the sites. If receiving a default route there's no way for other sites to detect the failure.

If receiving all the prefixes after MP-BGP convergence in ISP1 site N's prefixes will be withdrawn and will be reachable only via ISP2.

To use an active/standby

on all Cex

router bgp x

neighbor PE-ISP1 weigth 500

neighbor PE-ISP1 fast-external-fallover

in this way until a prefix is present in ISP1 MP-BGP traffic is sent via ISP1

If using two CE in each site things are a little more complex and you need an iBGP session between them.

Hope to help


PAUL CHEN Mon, 09/01/2008 - 15:37
User Badges:

Hi Giuseppe,

Thanks for the help. We may have 2 CEs in each site for each provider. So there are actually 4 CEs at each site.

Load balancing is between the 2 different providers.

So, I need to a ibgp peering session between the 2 CEs, please show me what else needs to be configured.

CE1 ---active--- PE_SP1


CE2 ---active--- PE_SP2

The standby links of each provider will back up their own active links, as shown in my earlier diagram

Thanks again,



This Discussion