LDP/TDP label allocation is, as per the standard behaviour (not talking about segment routing or PWs), a hop-by-hop behaviour, which is indeed very simple. After the labels are negotiated hop-by-hop, the incoming packet at the I-LSR is pushed an MPLS label to reach the upstream LSR for that specific destination. Consider the topology A-B-C-D, being A the I-LSR and D the E-LSR.
D distributes to C an LDP label for its IGP FECs, C to B, and so on so forth. An ingress packet hitting A, destined to a prefix advertised by D is pushed a label to reach the next-hop as per the RIB. B, then, swaps that label to reach the next second hop, and so on, so forth, until the packet reaches D, with C performing PHP. The players are then: IGP, LDP/TDP, and, ultimately, MPLS data plane forwarding (pushing/swapping and popping MPLS labels). This behaviour is however well covered by all the MPLS books you could find. Hope this helps. Nicola On Sat, Apr 13, 2013 at 8:41 AM, vishal bhugra <[email protected]>wrote: > Hello experts > > I was reading MPLS Fundamental book. In Chapter 2 page 36, they have > mentioned that MPLS Label do not have network level identifier. It is the > egress router that created label for the FEC and when that label arrives at > the Egress LSR it knows that this label belongs to which FEC. > > My question here is packets are classified at the ingress router and they > been allocated to a FEC. How do Egress LSR has communicated to Ingress > router that which label to choose for which FEC. > > May be I misunderstood, then what is correct and how Egress router know > that what is the payload of MPLS packet. > > I am not talking about MPLS VPN here, but the simple MPLS. > > > > -- > Thanks®ards > > Vishal > +91 8587900305 > > Best way to predict the future ..... is to create it > _______________________________________________ > For more information regarding industry leading CCIE Lab training, please > visit www.ipexpert.com > > Are you a CCNP or CCIE and looking for a job? Check out > www.PlatinumPlacement.com > > http://onlinestudylist.com/mailman/listinfo/ccie_rs > _______________________________________________ For more information regarding industry leading CCIE Lab training, please visit www.ipexpert.com Are you a CCNP or CCIE and looking for a job? Check out www.PlatinumPlacement.com http://onlinestudylist.com/mailman/listinfo/ccie_rs
