BGP/MPLS Layer 3 VPNs

[EdwardJStrange]

Hi!

I read this article about BGP/MPLS Layer 3 VPNs

https://www.noction.com/blog/bgp-mpls-layer3-vpn-practical-configuration 

Regarding the statement "The label 21 is the inner (VPN) label, added by the PE1 router", I did not understand how the label 21 was selected in this scenario?

Is there a BGP (or another protocol) message exchanged between PE1 and PE2 routers?

Regards.

[MHM Cisco World]

show mpls forwarding is answer 
you see that the prefix 172.16.2.0/24  have label 21. 
this label is used by other Peer to connect to this prefix.

[Paw_Paw]

I did not read the article, but the VPN label is exchanged through the MP BGP-update.

https://www.ccexpert.us/mpls/vpn-label-propagation.html

https://www.ccexpert.us/mpls/vpn-label-propagation.html

[David Ruess]

Hello,

Just like in LDP the BGP PE routers adds a VPN label to the route since you can have more than one label attached to a route (called a label stack).

In LDP the label can be a number between 16 and 1048575. 0-15 is reserved I believe. You can go trail this number with the label range command per router. Now that’s for MPLS. In BGP VPNv4 it also assigns the vpn label. That along with the RD and route make up the whole VPNv4 route. A quick search I couldnt find anywhere you can set a “label range or static entry” for those label types. So it may just choose it automatically to be unique.

As far as the sending of the info I believe it’s sent in the extended communities portion (along with  RT) since when you enable VPNv4 in BGP it automatically sends extended communities.

Hope this helps

-David