[c-nsp] Segment Routing (SR)

[Adam Vitkovsky]

Hi Saku,


>> What would be the drawbacks of using SPF/linkstate-based BGP for label 
>> propagation instead of ISIS or OSPF as IGP&LDP?
>I see no reason why it wouldn't work, however your iBGP sessions would 
>be unlabeled and routed natively. I personally prefer everything to be 
>labeled in my network.
 Well ISIS is CLNS and OSPF is pure IP that is no labels so the same would
apply for the hop by hop BGP sessions. 

>IGP is also always needed in SP network,
I'd like the BGP-LS to take over that role, with BGP-LS as IGP you would not
need to worry about scalability, so you could still have a separate area (AS
in case of BGP-LS) per each aggregation island for administrative purposes,
however you could pass full SR information into core AS and other
aggregation island. So there would be no need for yet another level of
abstraction i.e. RFC3017 and/or Opt.C. 

Also as we had the discussion about MPLS on the CPE devices, in case of
BGP-LS in the role of IGP&LDP you could control specifically which prefixes
and labels you accept into your LSDB. 

adam