RD and RT in MPLS

[John Blakley]

Are RDs recommended to be the same for a customer across the MPLS cloud or can they be different? What scenarios would require them to be different since BGP appends the RD to the route when sending through the network? I can get routes from both scenarios.

Thanks!

John

[vmiller]

Life is simpler if the RD & RT are the same. I have used that in an enterprise setting with no issues.

they can be different if you have the need to forward (or receive) a subset of routes another source 3rd party network management for example.

[Vaibhava Varma]

Hi j.blakley

I could think of one such scenario whereby using different RD for same Customer VRF would help us:

Lets consider the below setup for a dual homed Customer

               -------CE1AGWRTR1----------MPLSPE1------------MPLSBB-------------------MPLSPE3---------------

CE1ALAN       HSRP                                                 MPLS BB                                      HSRP        CE2A-LAN

            -------CE1AGWRTR2----------MPLSPE2------------MPLSBB-------------------MPLSPE4---------------

Customer is using MPLS VPN services to connect his two sites CE1A and CE2A in Dual-Homed Fashion

Now the customer uplink Peering to ISP on both sites CE1A and CE2A is low BW link and he wants to use both the uplinks in Active:Active mode for both reverse and forward traffic.For the forward traffic from the LAN side he achieves the same via HSRP Load Balancing by relevant config.

Now when we look at the reverse direction Load-Balancing both the GWRTRs should have route for the remote site learned via both remote MPLS-PEs ie

MPLS-PE1 should have route installed in the VRF both from MPLS-PE3 and MPLS-PE3. But by default because of MP-iBGP best path selection it will select only one of the remote PE and even if we enable the MP-iBGP load balancing the metric to both the remote PEs would be same or not we can not be certain . But here if we keep separate RD on each MPLS-PE for the particular Customer VRF those will be two separate vpnv4 routes and both would be installed in the Customer VRF and would help to send across traffic destined for the remote site to both the PEs. This way we would be able to achieve reverse traffic load-balancing also.

Hope I am correct in my though process and helps to answer your question.

Regards

Varma

[mlund]

Hi John

If Your network is using route-reflector for the ibgp then it's a good idea to use different rd:s if two pe:s is advertising the same prefix.

For example if both pe has rd 1:1 and advertise 10.0.0.0.

The RR will have have 2 pe:sadvertising 1:1:10.0.0.0 , the RR will pick one of them and advertise that one to the rest of the network

If one of the pe has rd 1:1 and the other pe has 1:2. The first one will advertise 1:1:10.0.0.0 and the other will advertise 1:2:10.0.0.0

This way the RR get two different prefixes, and will also spread both to the rest of the network .

/Mikael

[John Blakley]

That's a very good point Mikael...thank you!