[c-nsp] Segment Routing (SR)

[Adam Vitkovsky]

Hi Folks, 
What would be the drawbacks of using SPF/linkstate-based BGP for label
propagation instead of ISIS or OSPF as IGP&LDP? 

My point is:
For simple single AS deployments SR is a great simplification and brings
many enhancements. 
But as soon as you start to migrate your access areas into MPLS, ISIS might
start to get stuffed with high number of prefixes that it's not designed to
cope with, so you might need to involve the RFC3017 based Unified/Seamless
MPLS. 
Also from the perspective of inter-AS MPLS backbones based on RFC3017 -these
networks can only leverage SR within the single AS. 
Of course SR promises excellent high speed local-AS based convergence near
egress PE -as mentioned in section 3.3. of the Segment Routing Use Cases
draft -so there would be no need to wait for the RFC3017 to converge and the
PIC-core to kick in at the ingress PE. 
But still the end to end LSP would have to be built using a combination of
SR & RFC3017. 

So if such an essential change is being introduced into MPLS control and
data plane, why not to use link-state BGP as IGP&LDP? 


adam