Low latency forwarding failure detection

Thu Nov 4 15:17:27 UTC 2004

Not receiving any response for over a week after posting this query to
cisco-nsp I thought perhaps folks here might have some input.  In my
scenario, Cisco is the likely gear involved, but even if people have
vendor neutral feedback about this I'd be interesting in hearing it.

  From: John Kristoff <jtk at northwestern.edu>
  To: cisco-nsp at puck.nether.net
  Subject: Low latency forwarding failure detection
  Date: Tue, 26 Oct 2004 17:14:57 -0500
  X-Mailer: Sylpheed-Claws 0.9.12 (GTK+ 1.2.10; i686-pc-linux-gnu)

  I've got a situation where something like HSRP seems appropriate for a
  redundant default gateway configuration.  However, this application will
  want very low latency in finding and using the alternative gateway.
  Note, while the hosts have two NICs, they are both on the same subnet
  with one interface the default source and sink as long as it has link.
  I don't get to change this behavior.

  Default HSRP failure detection time however is likely not quick enough
  to bring a standby interface up to get traffic moving again.  I see that
  HSRP provides for hello and hold times in milliseconds.

  I have a few questions for people who may have had a need to get very
  low latency recovery of links and routers.  Have you used HSRP to do
  this?  On a typical local ethernet (gig) LAN configuration, what sorts
  of latencies and packet loss have you seen during a failure event?

  I'm cco-familiar with GLBP.  It appears to have essentially the same
  timing knobs with the ability to actively load balance traffic.  Is
  my assumption that some traffic will not experience any packet loss
  if it is not using the failed path correct?  For anyone who has used
  this, was the added complexity of this protocol worth it?

  As a general question... are people looking at implementing BFD?

    <http://www.ietf.org/html.charters/bfd-charter.html>

  Here I'm draft-familiar with what this is and I believe some vendors
  have code for it, but I've yet to try it.  I believe the spec is held
  up for security and IESG review.  This work looks very useful for some
  related applications going forward.  For this crowd, is this deployable
  and useful for minimizing forwarding failure time?

  This doesn't appear to be on the roadmap for HSRP/GLBP from what I
  can tell, but perhaps that would a worthwhile application of BFD?

  Are there other things people are doing (besides plain old load sharing)
  to get very low latency failover?

John