Subject: [mpls] New Comments on Segment Routing(3): Challenge of DoD and Inter-area extensions for SR-BE Path

From: Lizhenbin <[email-masked]>
Date: Thu, 22 Jan 2015 04:54:08 +0000

Hi all authors of segment routing,

This is the third comments.

              +-------+   +-------+   +------+   +------+
              |       |   |       |   |      |   |      |
           +--+ AGN11 +---+ AGN21 +---+ ABR1 +---+ LSR1 +--> to AGN
          /   |       |  /|       |   |      |   |      |
   +----+/    +-------+\/ +-------+   +------+  /+------+
   | AN |              /\                     \/     |
   +----+\    +-------+  \+-------+   +------+/\ +------+
          \   |       |   |       |   |      |  \|      |
           +--+ AGN12 +---+ AGN22 +---+ ABR2 +---+ LSR2 +--> to AGN
              |       |   |       |   |      |   |      |
              +-------+   +-------+   +------+   +------+

   static route     ISIS L1                ISIS L2
    LDP DoD         LDP DU                 LDP DU
   <-Access-><--Aggregation Domain--><---------Core--------->

Seamless MPLS has been proposed as one important architecture for network integration. As show in the
above the figure. In the access network between AN and AGNs, static route and LDP DoD are adopted.
There even more fetures related LDP in the scenarios: LDP proxy egress on AGN and Inter-area extensions
 of LDP. The challenge of proxy egress for SR has been proposed in the previous comments. I would like
to discuss the other two issues:
1. LDP DoD: In this scenarios, LDP DoD is adopted to set up LSP on demand which can controlled the number
of LSP. The control can be applied in the ingress node combing with the service supported(e.g. in the case,
if the configured LDP remote peer for PW service can trigger LDP DoD to send label request in AN). But for
SR, its floods the label mapping in the network. If hope to control the setup of LSP, the complex policy

must be applied on multiple nodes.
2. RFC5283 proposes the LDP inter-area extensions. That is, when search routes for the received labelp mapping,
longest-match method can also be adopted besides the exact match. Could you define clearly for SR what method

is adopted for SR-BE path? Could you explain the effects proposed by different methods if you had taken into

account the issue?

Regards,
Robin