Subject: [mpls] I-D Action:draft-ietf-mpls-ldp-igp-sync-04.txt

From: [email-masked]
Date: Wed, 17 Dec 2008 23:45:01 -0800 (PST)

A New Internet-Draft is available from the on-line Internet-Drafts directories.
This draft is a work item of the Multiprotocol Label Switching Working Group of the IETF.

	Title           : LDP IGP Synchronization
	Author(s)       : L. Fang
	Filename        : draft-ietf-mpls-ldp-igp-sync-04.txt
	Pages           : 8
	Date            : 2008-12-17

In certain networks there is a dependency on edge-to-edge Label 
Switched Paths (LSPs) setup by Label Distribution Protocol (LDP), 
e.g., networks that are used for MultiProtocol Label Switching 
(MPLS) Virtual Private Network (VPN) applications. For such 
applications it is not possible to rely on Internet Protocol (IP) 
forwarding if the MPLS LSP is not operating appropriately. 
Blackholing of labeled traffic can occur in situations where the 
Interior Gateway Protocol (IGP) is operational on a link but LDP is 
not operational on that link. While the link could still be used for 
IP forwarding, it is not useful for MPLS forwarding, for example, 
MPLS VPN; Border Gateway Protocol (BGP) route free core; or IP 
address carried in the packet is out of the RFC 1918 [RFC 1918] 
space. This document describes a mechanism to avoid traffic loss due 
to this condition without introducing any protocol changes.

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http://www.ietf.org/internet-drafts/draft-ietf-mpls-ldp-igp-sync-04.txt

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From: "Ilya Varlashkin" <[email-masked]>
Date: Thu, 18 Dec 2008 10:36:27 +0100

Hi,

I've just went through the draft and the way it deals with broadcast
networks seems to be quite harsh. Section 3 says that on broadcast links
traffic may be diverted from all nodes due to single LDP session. Even
if it's controlled by policy, this is heavy hit and undesirable.
Couldn't following solution work in case of ISIS used as IGP (haven't
thought yet of OSPF)?

1) if node involved in new LDP session setup is non-DR, delay advance
from INIT to UP until LDP sync is achieved (so neighbor state in the
ISIS TLV #240 is set to INIT for new LDP peer)
2) DR seeing HELLO PDU with such state should review all other HELLO
PDU's recently seen on the interface, and:
	a) if there are more PDU's listing that neighbor (LDP peer from
step 1) in non-UP state than PDU's listing it as UP, then set cost from
pseudo-node to that neighbor to 0xFFFFFE (when normally it's zero)
	b) if there are more UP PDU's than non-UP reset cost from
pseudo-node to that neighbor back to zero

Alternatively condition in step 2a could be strengthened to " if there
is at least one PDU with non-UP state set cost to 0xFFFFFE".

Could that work?

Cheers,
iLya