Routing

Hi guys!

I have a question. Here it is.

In l2vpn or l2circuit,  how does the PE forward the frame when a PE received a frame from CE, i mean based on layer2 header information and lookup the routing table routing-instance-name.l2vpn.0 or l2circuit.0 ? am i right.

Thanks guys!

Hi,

Basciallly L2VPN or L2CKT would act as a transparent pipe for data coming from CE. When the packet arrives on the CE facing interface, the entire packet becomes DATA PAYLOAD for the ingress PE router. Before forwarding this to the next-hop router, it pushes L2VPN/L2CKT label and then TRANSPORT MPLS label on top.

So the router in between the PEs would forward the packets based on the TRANSPOSRT MPLS label and when it finally reaches the egress PE router, it just forwards the packets based on the L2VPN/L2CKT label.

So basically the forwarding is not based on the l2 header information. However the L2/L3 information would be used for load-balancing on ECMP paths or Aggregated interfaces.

Regards

Surya Prakash

Hi, thanks!

You mean based on the frame from which CE facing interface arrived on, PE know how to forward the frame(push on vpn and mpls label), but where the interface and VPN label&MPLS label mapping information stored.

Hi,

That's the part of L2VPN/L2CKT signalling. If you would like to know which table, then it is mpls.0.

You can check with this command

show route table mpls.0 ccc <CE_INTERFACE> detail

Regards

Surya Prakash

Hi,

    I got it, thank you very much!