[c-nsp] VRF-LITE

[Bruce Pinsky]

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Sergio D. wrote:
> Thanks for your response.
> Can the VRF lite router able to route between VRFs? and if they have
> no relation to other VRFs on other routers, how come they use vrf
> route targets and all the works?


You may import/export route targets between VRFs within the same router.
The use of RDs and RTs within a VRF Lite router is simply the mechanism by
which the routing table instances are differentiated from each other (and
happens to be consistent with L3VPNs between PEs).  I like to think of VRF
Lite as a degenerative form of L3VPN where all the VPNs exist in the same
router (PE).

> We also have some PE routers with the same vrf route targets but
> without any MPLS configuration just ip tag switching on the interface,
> since they are only one hop away is the Label exchanged only with BGP?
> How can I check the VPN label?
> I know I need to RTFM, but not getting there fast enough :).
> 

Why do you differentiate MPLS from ip tag switching?  Tag switching is just
tag switching regardless of the label exchange protocol (LDP or TDP).

I think the thing to remember is that RFC4364 VPNs (formerly 2547bis) are
formed by exchanging routes with route targets via MP-BGP.  This allows
multiplexing of the control plane over a single BGP session instead of
multiple independent BGP sessions (i.e. full mesh of BGP sessions per VRF
per PE).  Since the core is ignorant to the specific VPN relationships, it
can switch the packets between PEs over "tunnels" by using label forwarding
(MPLS) or IP forwarding (L2TPv3).  In other words L3VPNs are enabled via
MP-BGP at the edge regardless of the method used to "tunnel" the packets
from PE->PE.

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bep

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