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

Uma Chunduri <> Mon, 11 April 2016 21:45 UTC

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From: Uma Chunduri <>
To: Eric C Rosen <>, Xuxiaohu <>, "" <>
Thread-Topic: [mpls] Clarification on the motivation of draft-xu-spring-islands-connection-over-ip-05
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Date: Mon, 11 Apr 2016 21:45:08 +0000
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Subject: Re: [mpls] Clarification on the motivation of draft-xu-spring-islands-connection-over-ip-05
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In-line [Uma]:

Uma C.

-----Original Message-----
From: Eric C Rosen [] 
Sent: Monday, April 11, 2016 11:59 AM
To: Uma Chunduri; Xuxiaohu;
Subject: Re: [mpls] Clarification on the motivation of draft-xu-spring-islands-connection-over-ip-05

>> [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?

[Uma]: I was describing more of #2. However #1 is one of the cases. 
              In #2 as the shortest path neighbor doesn't support SR (and no outgoing LDP/RSVP label) and it recognizes the same, it encapsulates in IP or 
              as per the  egress node N's tunnel de-capsulation capabilities. 
              There is no additional computation required here and  its still shortest path towards egress but not labeled.