how LSP is established in MPLS-VPN

hichamlechqar · ‎04-20-2014

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 )

Muhammad Thanveer · ‎04-21-2014

when you enable vpnv4 or 6 there will be a stack of the label which identifies what is the Local Label and which vpnv4 or 6 label it has attached and when it goes to the other end PE first vpnv4 label will be poped and then it ideniies the local mpls label and sends it accordingly I am not considering the PHP, if PHPs is there then before one hop the label will be popped

Hope you understand and if you feel I misunderstood your question please elaborate.

BR

Thanveer

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hichamlechqar · ‎04-25-2014

don't worry i really understood thanks you for your helps

Nagendra Kumar Nainar · ‎04-21-2014

Hi,

Just to elaborate what Tanveer said....

VPN can be considered as a service running on top of MPLS. So in your case,

CUST1 (10.10.10.1) ---(VRFA)PE1 ----P1 ------P2 ----PE2(VRFA) ----- CUST2 (20.20.20.2)

You will have BGP enabled between PE1 and PE2 to advertise/exchange VRFA prefixes. PE2 will assign Label L22 for 20.20.20.2 and advertise (via BGP) to PE1 with PE2 as nexthop (say loopback address). PE2 will also have advertised its loopback address via IGP to P/PE1 nodes and assign local label for loopback address and advertise via LDP (in this case it will be POP). P1 node connected to PE1 will assign L2 for loopback of PE2 and advertise to PE1.

PE1 will now impose 2 labels when it wants to send a traffic destinated to 20.20.20.2. On receiving the packet from CUST1, it will impose label L22 (received from PE2 via BGP) and Label L2 received via LDP from P nodes. P2 node will pop the top label and send the packet with label L22 untouched. THis will be used by PE2 to identify the VRF and forward the traffic.

The LSP between PE1 and PE2 is simply known as Transport LSP. Irrespective of any number of prefixes or VRFs between PE1 and PE2, you only need one transport LSP and the underlying label (L22 in this case) will help identify the VRF or prefixes.

HTH,

Nagendra

hichamlechqar · ‎04-22-2014

thanks for your answer

Muhammad Thanveer · ‎04-23-2014

You are Always Welcome

BR

Thanveer

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