You are talking about two things at once. Routing a packet is different then advertising a route. When a router receives an advertisement, it looks at the RT so it knows what VPN it belongs too. Then it stores it using the RD, which uniquely identifies the route from all the other routes. When the PE router receives a packet, it has 2 labels (actually 1 because of PHP). The outer one (which has been popped) is for its own loopback. The last label now corresponds to the VPN/interface to which the packet should be forwarded. If this label did not exist, the router would not know which VPN or interface the packet should be forwarded.
On Thu, Feb 11, 2010 at 3:11 PM, Mashburn, Vince <[email protected]>wrote: > OK, so when the transport label is stripped off, the VPN label tells the > router which VRF table to inject the packet into. Once that is done, the > router looks at the RT to determine if the route is valid to export to the > customer. Is that correct? > > > > Thanks, > > Vince Mashburn > > HP Americas Technology Services > > Account Services Manager > > FedEx On-site Office Phone: 901-263-6498 > > Mobile: 901-569-9734 > > > > > > *From:* Bryan Bartik [mailto:[email protected]] > *Sent:* Thursday, February 11, 2010 4:06 PM > *To:* Mashburn, Vince > *Cc:* [email protected] > *Subject:* Re: [OSL | CCIE_RS] MPLS VPN Label > > > > Vince, > > The Route target identifies the route, but does not identify the packet > itself. Perhaps if there was an "RT" field in the IP header, you wouldn't > need the VPN label at all :) > > On Thu, Feb 11, 2010 at 2:48 PM, Mashburn, Vince <[email protected]> > wrote: > > OK. I am a little confused with the VPN label in MPLS. I completely > understand the Transport label, but I thought that all of the VPN > information was carried within the Route-Target extended BGP community. Why > do you also need a label to identify the VPN? > > > > > > Thanks, > > Vince Mashburn > > HP Americas Technology Services > > Account Services Manager > > FedEx On-site Office Phone: 901-263-6498 > > Mobile: 901-569-9734 > > > > > > > _______________________________________________ > For more information regarding industry leading CCIE Lab training, please > visit www.ipexpert.com > > > > > -- > Bryan Bartik > CCIE #23707 (R&S, SP), CCNP > Sr. Support Engineer - IPexpert, Inc. > URL: http://www.IPexpert.com > -- Bryan Bartik CCIE #23707 (R&S, SP), CCNP Sr. Support Engineer - IPexpert, Inc. URL: http://www.IPexpert.com
_______________________________________________ For more information regarding industry leading CCIE Lab training, please visit www.ipexpert.com
