Re: mpls vpn route-target

On Mon, Nov 2, 2009 at 19:54, Ivan <ivanzghr_at_gmail.com> wrote:
> Yes, if I put import also on R3 it works. But now I'm confused how
> come that it works when you just put this on R4 (like solution of the
> task specifies):
>
> ip vrf VPNB
> B route-target both 1:105

Doing "route-target both X:Y" in VRF definition section is the same as
doing both import *and* export for that RT. Also, notice that each VRF
can set more than one RT extended community on prefixes that it
advertises, as well as import prefixes with several RTs. Now, armed
with that knowledge, let's proceed.

ip vrf VPNB
 route-target both 1:105
!

equals:

ip vrf VPNB
 route-target import 1:105
 route-target export 1:105
!

Since boh PEs with VPNA already import 1:105, prefixes advertised as
part of VPNB will be imported if they have this RT attached.
Similarly, since VPNA PEs are advertising prefixes with 1:105
attached, R4 will now import these routes into VPNB.

Another thing to notice - VRF definitions are *local* to the router.
If you have multiple routers supporting "same VRF", they do so only if
they are configured with proper import/export statements. This allows
us more advanced configurations, like extranet, central services and
even more exotic ones, like half-duplex VRFs.

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