MPLS RT

[rajeshk200_2]

I have been scratching my head around to understand how export RT's attached while implementing central services with isolation between customer sites.

lets say

client 1

ip vrf client1

rd 100:100

route-target both 100:100

route-target import 300:300

client2

ip vrf client2

rd 200:200

route-target both 200:200

route-target import 300:300

Central

ip vrf central1

rd 300:300

route-target both 300:300

route-target import 100:100

route-target import 200:200

I am inclined to think this will lead to connectivity between two sites via central services ,  central services vrf import all client routes in it's vrf (with

route-target import 100:100,  route-target import 200:200) and then export all the routes with rt 300:300 which are getting imported into client vrfs.

I know I am wrong , but I'm trying to think how client segments gets isolated when they have connectivity with central services.

will central services only export routes originated from local vrf? , if yes then how.

thanks

Rajesh

[Peter Paluch · Accepted solution]

Hello Rajesh,

A key fact to remember is that a route-target set once is not changed when readvertising routes further. The Central router may receive routes from both Client1 and Client2, but it will not change their RTs. Routes from Client1 will continue to have the RT set to 100:100 and routes from Client2 will continue having the RT set to 200:200. Only the locally-injected routes on the Central router will have their RT set to 300:300.

Let's examine this in a closer detail. In your example, Client1 exports routes with the RT set to 100:100, Client2 exports routes with RT set to 200:200, and Central exports routes with 300:300.

Now, Client1 imports routes with 100:100 and 300:300 which means it accepts its own routes plus routes from the Central location described by RT 300:300.

In a similar fashion, Client2 imports routes with RT 200:200 and 300:300, i.e. its own routes plus routes from the Central location having RT 300:300.

Client1 will not accept routes from Client2 because routes exported from Client1 have their RT set to 100:100, and Client2 accepts only routes having RT set either to 200:200 or 300:300. As the RT set by Client1 and received at the Central does not change when Central advertises the routes to Client2, the Client2 will not accept these routes because their RT is different from Client2's import list.

Best regards,

Peter

[rajeshk200_2]

Many thanks Peter, This was the information I was after. I was thinking that rt stripped off when gets in to vrf routing table and again gets attached when exports.

Regards

Rajesh