[Idr] SR-Capabilities TLV in draft-ietf-idr-bgp-ls-segment-routing-ext-01

Simon Zhong <szhong@juniper.net> Sun, 09 April 2017 18:20 UTC

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From: Simon Zhong <szhong@juniper.net>
To: "idr@ietf.org" <idr@ietf.org>
Thread-Topic: SR-Capabilities TLV in draft-ietf-idr-bgp-ls-segment-routing-ext-01
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Date: Sun, 9 Apr 2017 18:20:46 +0000
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Subject: [Idr] SR-Capabilities TLV in draft-ietf-idr-bgp-ls-segment-routing-ext-01
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Hi,

I'm working on Wireshark bgp dissector and following description confuses me.

2.1.1.  SR-Capabilities TLV

   The SR Capabilities sub-TLV has following format:
......
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Range Size                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   //                SID/Label Sub-TLV (variable)                 //
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

This implies that there's one "Range Size" and one or more "SID/Lable Sub-TLV), however later in this section, it says:

     One or more entries, each of which have the following format:

         Range Size: 3 octet value indicating the number of labels in
         the range.

         SID/Label sub-TLV (as defined in Section 2.3.7.2).

Which sounds like one or more "Range Size" + "SID/Lable sub-TLV" combo are allowed.

The same applies to SR Local Block TLV as well.

So what's the intended behaviour? Thanks.

/Simon