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Symmetric routing on MPLS

I want to ensure both inbound and outbound traffic between Site A and Site B use the same link based on PBR.  I plan on using PBR to isolate outbound time sensitive traffic (voice, video) to Link A and all other traffic to Link B, but need to make sure all return traffic is also dedicated to its respective link.  The sites are conencted via a SPRINT MPLS, dual 50Mbps ethernet circuits using BGP and terminating on one CE router at each site. 



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Re: Symmetric routing on MPLS

Hello Abbas,

the SP network is shared with PBR you can only choice the PE-CE link on the sending side. On the remote site the PE device can choice any of the two PE-CE links.

In order to ensure the use of dedicated PE-CE links in both sites the MPLS SP should implement two different VRFs in order to avoid to mix traffic between links.

This requires cooperation with the SP tech stuff and this is the request you should make to them.

In any case even using two VRFs, the same backbone links are used within the SP network. So sensitive traffic has to be appropriately marked in order to get better treatement within the SP cloud.

And the marking has to be agreed with the MPLS SP.

Hope to help


Symmetric routing on MPLS


are you able to use a separate subnet on each site for the time-sensitive devices?

And are the CE routers peering to a different PE on each line?

If yes, you might possibly modify the BGP attributes to make the traffic sent between those two subnets to use one line on each site only?

For example:

You could advertise the time-sensitive subnet with the site AS number prepended several times to Line B.

And you could configure a route-map giving a better Local Preference to the time-sensitive subnet prefix received from the other site on Line A. (And giving a worse Local Preference to all other prefixes recived on that Line.)

This way (if the MPLS SP does not set anything special) the traffic sent between the time-sensitive subnets would always be sent through Lines A.

On the other hand, also all outgoing traffic sent from other subnets on one site to the time-sensitive subnet on the other site would take the Line A.

Should that be a problem, you could use PBR to make that traffic to use Line B?



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