VPLS Multihoming on Junos - FEC confusion‏

Question

I'm going over the VPLS multihoming options on Juniper's web site. I'm not concerned with LAG and MC-LAG for the moment.

As far as I'm aware:

• FEC128 is when you are using manual discovery of pseudowires (LDP)
• FEC129 is when you are using BGP auto-discovery.

Juniper techpub for FEC129 multihoming I don't have a problem with as Juniper shows how to multihome with BGP.

The FEC128 multihome techpub says that you cannot enable LDP signalling, you have to use BGP signalling.

I know that you can use LDP for manual discovery and LDP will then signal VC labels. You can also use BGP for auto-discovery and LDP for VC label signalling. You can also use BGP for both.

What I don't get is how you could use FEC128 with BGP signalling. Junos doesn't give you the option to only signal through BGP but manual discovery through LDP.

So my question is, when exactly would the FEC128 config be used over the FEC129 config? If you are using BGP for signalling are you not using BGP for discovery at the same time?

Or maybe I'm just misunderstanding something?

Answer 1

Part of it comes down to what's supported, you might have PE's running older code that don't support FEC129.

• FEC128 multihoming was introduced in Junos 7.5 (see here).
• FEC129 multihoming was introduced in Junos 12.3 (see here).

It's not necessarily that a single VPLS domain ONLY signals with BGP and ONLY discovers with LDP, it's the fact that you can interoperate within the FEC 128 standard (and FEC129). I definitely think you're usually going to select one and run with it, but there are all kinds of environments out there.

FEC128 on Junos will support running individual mesh groups inside of a single VPLS instances (1 or more group of LDP signaled PE's, 1 group for BGP signaled PE's). You can configure them to interoperate by configuring a border PE to be a member of both the BGP signaled group, and LDP signaled group. That way if you are signaling with LDP in one area, and you want to introduce BGP in another - both can work together.

Here's some extra material/examples, if you're interested:

http://www.juniper.net/techpubs/en_US/junos13.1/topics/task/configuration/vpls-bgp-ldp-signaling-solutions.html

http://www.juniper.net/techpubs/en_US/junos14.1/topics/usage-guidelines/vpns-configuring-interoperability-between-bgp-signaling-and-ldp-signaling-in-vpls.html#jd0e120

Answer 2

I'm not sure that FEC128 is limited to just manual discovery of PWs.

I've always used the FEC128 multi-home method described in the link with BGP auto-discovery and it works just fine - if I understand your question correctly.