Maximum Transmission Unit Signalling Extensions for the Label Distribution Protocol
RFC 3988

Approval announcement
Draft of message to be sent after approval:

From: The IESG <iesg-secretary@ietf.org>
To: IETF-Announce <ietf-announce@ietf.org>
Cc: Internet Architecture Board <iab@iab.org>,
    RFC Editor <rfc-editor@rfc-editor.org>, 
    mpls mailing list <mpls@lists.ietf.org>, 
    mpls chair <mpls-chairs@tools.ietf.org>
Subject: Document Action: 'Maximum Transmission Unit Signalling 
         Extensions for the Label Distribution Protocol' to Experimental 
         RFC 

The IESG has approved the following document:

- 'Maximum Transmission Unit Signalling Extensions for the Label 
   Distribution Protocol '
   <draft-ietf-mpls-ldp-mtu-extensions-04.txt> as an Experimental RFC

This document is the product of the Multiprotocol Label Switching Working 
Group. 

The IESG contact persons are Alex Zinin and Ross Callon.

A URL of this Internet-Draft is:
http://www.ietf.org/internet-drafts/draft-ietf-mpls-ldp-mtu-extensions-04.txt

Technical Summary
 
   Proper functioning of RFC 1191 path Maximum Transmission Unit (MTU)
   discovery requires that IP routers have knowledge of the MTU for each
   link to which they are connected.  As currently specified, the Label
   Distribution Protocol (LDP) does not have the ability to signal the
   MTU for a Label Switched Path (LSP) to the ingress Label Switching
   Router (LSR).  In the absence of this functionality, the MTU for each
   LSP must be statically configured by network operators or by
   equivalent, off-line mechanisms.
 
Working Group Summary
 
 The WG originally submitted the doc for PS. However, since no 
 implementations have been identified, the target status has been
 changed to Experimental.
 
Protocol Quality
 
 The document has been reviewed for the IESG by Alex Zinin.

RFC Editor Note

1. Disregard the following lines in the document header:

   "Updates: 3036"
   "Category: Standards Track"

   The document target status in Experimental.

2. Second para in Abstract:

   OLD:
   
    This document specifies extensions to LDP in support of LSP MTU
    discovery.

   NEW:

    This document specifies experimental extensions to LDP in support
    of LSP MTU discovery.

3. Section 5.1 "Interaction With LSRs Which Do Not Support MTU Signalling"

   OLD:
   
   Changes in MTU for sections of an LSP may cause intermediate LSRs to
   generate unsolicited label Mapping messages to advertise the new MTU.
   LSRs which do not support MTU signalling MUST accept these messages,
   but MAY ignore them (see Section 2.1).

   NEW:

   Changes in MTU for sections of an LSP may cause intermediate LSRs to
   generate unsolicited label Mapping messages to advertise the new MTU.
   LSRs which do not support MTU signalling will, due to message and TLV
   processing mechanisms specified in RFC3036 [2] accept the messages
   carrying the MTU TLV, but will ignore the TLV and forward the TLV
   to the upstream nodes (see Section 2.4).

    
4. Section "Security Considerations"

   OLD:

   This mechanism does not introduce any new weaknesses in LDP.  It is
   possible to spoof TCP packets belonging to an LDP session to
   manipulate the LSP MTU, but LDP has mechanisms to thwart these types
   of attacks.

   NEW:

   This mechanism does not introduce any new weaknesses in LDP.  It is
   possible to spoof TCP packets belonging to an LDP session to
   manipulate the LSP MTU, but LDP has mechanisms to thwart these types
   of attacks. See section 5 of [2] for more information on security
   aspects of LDP.