North American Network Operators Group

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RE: What Worked - What Didn't

  • From: Iljitsch van Beijnum
  • Date: Mon Sep 17 18:12:44 2001

On Mon, 17 Sep 2001, Randy Bush wrote:

> > "The suggested value for the Hold Time is 90 seconds.  The suggested value
> > for the KeepAlive timer is 30 seconds."

> the hello timer != noticing an interface has gone hard down, which i thought
> was your original point.

If there are no other means to detect the datalink session between two
BGP speakers has gone south, the hold timer will do this.

For POS and most other point-to-point links the "fast-external-fallover"
will usually kick in sooner because datalink layer keepalives aren't
received anymore (some advocate "no fast-external-fallover" to avoid
flapping, though), but in switched environments such as Ethernet or ATM
the interface may stay up while there is no connectivity. In those
circumstances, the hold timer is the only thing that will break the BGP
session eventually.