Nov 20 2008
Non VPN transit providers – Option 4?
There can be cases where two MPLS VPN service providers would like to deliver an MPLS VPN service to a customer using a non-VPN transit provider ie this non-VPN transit provider has an MPLS infrastructure, but does not deliver MPLS VPN services.
This architecture is sometimes referred to as Option 4(This is not mentioned in section 10 RFC 4364).
Topology as below.
There are two variations in the implementation, the variations in implementation are with respect to how the label information is advertised across the MPLS VPN service provider networks.
1-In variation 1 the ASBR redistributes the learned IPv4 prefixes into the local IGP. A label is then generated and advertised through the network.
2-In variation 2 the ASBR advertised the learned IPv4 prefixes and IPv4 labels using iBGP directly to either the PE or Route reflector.
An LSP is constructed from a PE in one AS to another PE in the destination AS via the non-VPN transit provider.
The route reflectors in the MPLS VPN Service Providers establish an MP-eBGP session to transport VPNv4 prefixes. The route reflectors advertise the prefixes with the next hop unchanged using the command below.
neighbor rr-ip-address next-hop-unchanged
The original VPN label generated by the source PE does not change anywhere in the path.
The link between the ASBRs in the different ASs is a non LDP link, the MPLS signalling carried out over the link is done via BGP (read about BGP MPLS signalling).
