Subject: RE: [Isis-wg] Status of some drafts

From: Jeff Parker <[email-masked]>
Date: Wed, 10 Oct 2001 09:33:08 -0400

> > The 3-way handshake ... [is]
>
> stuck in 'will be RFC any minute now' status. 

Pity there is no way to have a semi-official
link to docs that are between stools.  

I have a bootleg copy of draft-ietf-isis-3way-03.txt 
that I'd be happy to forward to those who need to 
implement but don't have any text.  

- jeff parker  
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Isis-wg mailing list  -  [email-masked]
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---

From: Jeff Parker <[email-masked]>
Date: Wed, 10 Oct 2001 15:21:49 -0400

> Can any body explain the idea of three way handshake for ISIS or give
> some draft about this topic? (Sorry, I am new to this mailing-list)
> 
> Jing
 
Jing -

From the draft.  

   The IS-IS protocol [1] assumes certain requirements stated in ISO
   10589 (section 6.7.2) for the operation of IS-IS over point-to-point
   links and hence provides only a two-way handshake when establishing
   adjacencies on point-to-point links.  The protocol does not operate
   correctly if these subnetwork requirements for point-to-point links
   are not met.  The basic mechanism defined in the standard is that
   each side declares the other side to be reachable if a Hello packet
   is heard from it.  Once this occurs, each side then sends a Complete
   Sequence Number PDU (CSNP) to trigger database synchronization.

   Three failure modes are known.  First, if the link goes down and then
   comes back up, or one of the systems restarts, and the CSNP packet is
   lost, and the network has a cut set of one through the link, the link
   state databases on either side of the link will not synchronize for a
   full LSP refresh period (up to eighteen hours).

   A second, more serious failure, is that if the link fails in only one
   direction, the failure will only be detected by one of the systems.
   Normally, this is not a serious issue;  only one of the two systems
   will announce the adjacency in its link state packets, and the SPF
   algorithm will thus ignore the link.  However, if there are two
   parallel links between systems and one of them fails in one
   direction, SPF will still calculate paths between the two systems,
   and the system that does not notice the failure will attempt to pass
   traffic down the failed link (in the direction that does not work).

   In addition, SONET links bring a third issue, which is that when
   SONET protection is used, a system may receive packets that are
   actually destined for a different system (or a different link on the
   same system).  The receiving system may end up thinking that it has
   an adjacency with the remote system when in fact the remote system is
   adjacent with a third system.

   The solution proposed here ensures correct operation of the protocol
   over unreliable point-to-point links. As part of the solution to the
   three-way handshaking issue, a method is defined for supporting more
   than 256 point-to-point interfaces which is more robust than the ad
   hoc methods currently in use.

I will send you a copy of the draft off-line.  

- jeff parker
- axiowave networks