MPLS, Summarisation, OSPF and stubby areas

[olorunloba]

Since summarisation breaks the LSP and this is not desired in an MPLS VPN network on the core, can it be concludded then that stubby areas can not be used on the service provider core, if he wants to offer MPLS VPN service?.

Or how does he avoid or workaround the issue of summarisation, small Link State Database and areas on the core.

[Harold Ritter · Accepted solution]

You are correct. It is not possible to use stubby areas if you want to deploy MPLS VPN. You can still summarize though as long as you don't summarize the IP addresses assigned to the loopback interfaces. One way to do it is to use a different address range for the loopback interface of all your PEs and to use summarization for all address ranges but this one. This way only the loopback addresses will be advertised as /32 and the rest of your prefixes will be nicely summarized.

Hope this helps,

[olorunloba]

Hmmmmm,

So I can summarise the rest of addresses used on my transmission backbone, once the loopback addresses are not part of it. I assume that this would work becasue the BGP sessions are sourced from the loopback addresses (which is the practice anyway).

[Harold Ritter]

Correct. For MPLS VPN to work properly, the LSP has to be end to end. The issue with summarization you change the FEC and by doing that you break the end to end LSP.

Hopr this helps,