Re: [mpls] Clarification on the motivation of draft-xu-spring-islands-connection-over-ip-05

Eric C Rosen <erosen@juniper.net> Mon, 11 April 2016 18:58 UTC

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To: Uma Chunduri <uma.chunduri@ericsson.com>, Xuxiaohu <xuxiaohu@huawei.com>, "spring@ietf.org" <spring@ietf.org>
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From: Eric C Rosen <erosen@juniper.net>
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Subject: Re: [mpls] Clarification on the motivation of draft-xu-spring-islands-connection-over-ip-05
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>> [Eric] It would be somewhat unusual to have an IGP domain in which some nodes support MPLS and some don't.
> [Uma] May be true with non-SR and traditional  MPLS.
> But with SR I am working with one customer where MPLS (as SR data plane) is brought into their pure IGP-IP domain.
> With static PW labels (inner label)  currently pure soft GRE encap is being used (for transport)  but SR is being planned from EPG to cell site routers eventually.
> Planning slow upgrade for some of the MBH nodes with SR-MPLS data plane.  In this case its quite possible to use (in future) non-shortest path SR label stack.
>
>
Interesting.  But I'm not sure which of two scenarios you are describing:

1. There is always an MPLS path from ingress to egress, but the shortest 
path may not consist entirely of MPLS-capable nodes.

2. There isn't always an MPLS path from ingress to egress.  So if the 
ingress creates an MPLS packet, some intermediate node may need to 
re-encapsulate the packet  in IP, in order to get the packet delivered 
to the egress node.

Or is the scenario different from either of these two?