Subject: RFC4577 Question

From: David Freedman <[email-masked]>
Date: Mon, 6 Feb 2012 14:38:48 +0000

Hiya,

I have a question pertaining to RFC4577

"OSPF as the Provider/Customer Edge Protocol for
BGP/MPLS IP Virtual Private Networks (VPNs)"

RFC4577 makes the following requirement of creating
Sham Links (Sec 4.2.7.3):

--------------

   An OSPF protocol packet is regarded as having been received on a
   particular Sham Link if and only if the following three conditions
   hold:

      -  The packet arrives as an MPLS packet, and its MPLS label stack
         causes it to be "delivered" to the local Sham Link endpoint
         address.

      -  The packet's IP destination address is the local Sham Link
         endpoint address.

      -  The packet's IP source address is the remote Sham Link endpoint
         address.

---------------

Can I ask why a requirement for the OSPF protocol
packet to be MPLS exists?

Imagining that only the CE router runs OSPF, and runs BGP with
the PE router, since the (OSPF) routing information is injected
into the BGP at the PE router, and also labelled (As per RFC4364)
, surely an MPLS LSP directly from the OSPF endpoint is not required?
 
I currently have a use-case whereby I do not wish to run the OSPF
protocol on the PE router, but am happy to do this on the CE,
I'd like to be able to form the sham link between the CE routers,
without having to introduce MPLS to them, since I speak BGP with
the PE which is capable of labelling, and the BGP is also responsible
for consistent routing between the two, surely this restriction
shouldn't need to exist?

Regards

David Freedman

Claranet

---

From: Acee Lindem <[email-masked]>
Date: Mon, 6 Feb 2012 09:52:33 -0500

Hi David, 
You are envisioning a topology that is not supported by RFC4577. You simply cannot have a sham link w/o running OSPF on the PE. 
I've been in discussions of running OSPF as an OTT protocol but there is no standard and it is not RFC4577. 
Hope this helps,
Acee