Subject: Re: [Pce] 'Re: draft-ietf-pce-segment-routing-00'

From: "Daniel King" <[email-masked]>
Date: Sun, 1 Mar 2015 22:04:18 -0000

Hi All, 

Unfortunately the contents of the email from Joydeep was removed when it arrived at the list. Below is the original message/question. If the segment routing authors could respond, I am sure it would be appreciated. 

BR, Dan. 

From: Joydeep Banerjee [email-masked] <mailto:[email-masked]> 

Re: draft-ietf-pce-segment-routing-00

Sec 5.1.1.1 - Exchanging SR Capability - number of SID (MSD value) is negotiated at the PCEP session level. This is initiated only by the head end PCC based on its data plane capability. However shouldn't it also account for the finite label stacking ability of MPLS data plane for transit routers? Let us assume, head end PCC (say S) can handle a MPLS label stack depth of 10 (i.e. MSD = 10), so PCEP sessions is initiated by S with OPEN message carrying SR-PCE-CAPABILITY MSD = 10 to SR capable PCE of its choice. Next S has a requirement to get a SR TE path to destination D and consults SR capable PCE. PCE gets back to S with a label stack of 7 (less that MSD of 10). So S appends 7 SIDs from SR-ERO in LIFO order to the outgoing packets to C (the next SR enabled router towards D). C pops the topmost label and tries to forwards the packet, but it appears that it's data plane can't support more than 2 MPLS label stack. So C drops the packets.

How do you handle the scenario?

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