Re: [Idr] REVISED Last Call: <draft-ietf-idr-ls-distribution-10.txt> (North-Bound Distribution of Link-State and TE Information using BGP) to Proposed Standard

Balaji Rajagopalan <> Wed, 01 April 2015 17:00 UTC

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From: Balaji Rajagopalan <>
To: "" <>, Hannes Gredler <>
Thread-Topic: [Idr] REVISED Last Call: <draft-ietf-idr-ls-distribution-10.txt> (North-Bound Distribution of Link-State and TE Information using BGP) to Proposed Standard
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Subject: Re: [Idr] REVISED Last Call: <draft-ietf-idr-ls-distribution-10.txt> (North-Bound Distribution of Link-State and TE Information using BGP) to Proposed Standard
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I seek a correction to the following text in section

IGP Router ID: <snip> For an OSPFv2 "Pseudonode" representing a LAN,

      this contains the 4 octet Router-ID of the designated router (DR)
      followed by the 4 octet IPv4 address of the DR's interface to the
      LAN (8 octets in total) <snip>"

The reason I seek this change is, the transit link representation in OSPFv2 router-LSA does not contain the router-id of the DR (section of RFC2328). So, BGP-LS has nowhere to derive Router-ID from.

Below are more details with an example.

The 'IGP router ID' field can appear either in ‘Local Node Descriptor’ or ‘Remote Node Descriptor’. Let’s consider the case in which this field appears in ‘Remote Node Descriptor’ in the following topology.

R1( <----L1----> R2 (

R1's router-id is, and L1 interface IP address is
R2's router-id is, and L1 interface IP address is
L1 is a LAN.
R1 is elected as the DR for L1.

There are four distinct unidirectional links in the topology above: R1->DR, DR->R1, R2->DR, and DR->R2. Let’s consider the link R2->DR. R2’s router LSA represents R2->DR link as follows: -

Advertising router:
   Link ID:
   Link data:
   Type:2 (Transit)

Note that the OSPF link representation above does not include the router-id of the DR, which is

According to the text in section, BGP-LS requires us to represent R2->DR link as follows (considering only node descriptors of relevance to this discussion, and ignoring the remaining fields) : -

Local Node(IGP-Router-Id: -> Remote Node(IGP-Router-Id:

However, the OSPF representation of the above link in R2’s router LSA does not contain at all. Therefore, BGP-LS has nowhere to derive ‘’ from, for the link R2->DR.

The example in section 3.7 is at odds with the text in section, and represents the link as follows (which works perfectly): -

Local Node(IGP-Router-Id: -> Remote Node(IGP-Router-Id:

I suggest rewording the text in as follows:

IGP Router ID: <snip> For an OSPFv2 "Pseudonode" representing a LAN,

      this contains the 4 octet IPv4 address of the DR's interface to the
      LAN, followed by any non-zero 4-octet number (8 octets in total) <snip>”

Balaji Rajagopalan

From: The IESG <<>>
Reply-To: "<>" <<>>
Date: Thursday, March 19, 2015 at 1:10 AM
To: IETF-Announce <<>>
Cc: "<>" <<>>
Subject: [Idr] REVISED Last Call: <draft-ietf-idr-ls-distribution-10.txt> (North-Bound Distribution of Link-State and TE Information using BGP) to Proposed Standard

The IESG has received a request from the Inter-Domain Routing WG (idr) to
consider the following document:
- 'North-Bound Distribution of Link-State and TE Information using BGP'
  <draft-ietf-idr-ls-distribution-10.txt> as Proposed Standard

The IESG plans to make a decision in the next few weeks, and solicits
final comments on this action. Please send substantive comments to the<> mailing lists by 2015-04-08. Exceptionally, comments may be
sent to<> instead. In either case, please retain the
beginning of the Subject line to allow automated sorting.


   In a number of environments, a component external to a network is
   called upon to perform computations based on the network topology and
   current state of the connections within the network, including
   traffic engineering information.  This is information typically
   distributed by IGP routing protocols within the network.

   This document describes a mechanism by which links state and traffic
   engineering information can be collected from networks and shared
   with external components using the BGP routing protocol.  This is
   achieved using a new BGP Network Layer Reachability Information
   (NLRI) encoding format.  The mechanism is applicable to physical and
   virtual IGP links.  The mechanism described is subject to policy

   Applications of this technique include Application Layer Traffic
   Optimization (ALTO) servers, and Path Computation Elements (PCEs).

The file can be obtained via

IESG discussion can be tracked via

The following IPR Declarations may be related to this I-D:

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