how LSP is established MPLS VPN

hichamlechqar · ‎04-23-2014

hey everybody

i know that LSP without vpn MPLS , is performed like that :
CUST1 (10.10.10.1) ---PE1 ----P ------P ----PE2 ----- CUST2 (20.20.20.2)
PE2 assigned a label (L1) to FEC 20.20.20.2 and sent at P this last receive (L1) and swap it to P with (L2) and the same thing for PE1.
the P in this case without vpn MPLS know the CEF 20.20.20.2 in LFIB table because it assigned label at 20.20.20.2
my problem is that in MPLS VPN the P not known CEF 20.20.20.2 (VRF A + label VPN) therefore how LSP is established in step when PE2 add 2 label ,one for VPN and second label for which FEC ? it is 20.20.20.2 if yes the 20.20.20.2 is not known in RIB
please some one explain me step to performed LSP in above case.
i have the same for 6PE (LSP for P )

rais · ‎04-23-2014

For MPLS VPN network, usually all PEs know how to get to other PE routers via LSP tunnels. These are transport/outer tunnels/labels.

Over the transport tunnel, PE2 advertises to PE1 via BGP, to use a label L for 20.20.20.2. This L is inner label that is put on the packet leaving PE1, then PE1 also puts an outer/transport label on the packet as it exists out. All intermediate P routers just look at the transport/outer label to guide the packet all the way to PE2. PE2 knows what inner label is and guides the packet to correct interface for 20.20.20.2.

HTH.