Subject: Re:

From: divya mattey <[email-masked]>
Date: Thu, 24 May 2001 10:27:17 +0100 (BST)

Hi,
Can anybody tell me what is 'auto refresh loop' in
RSVP? RFC2205 is not very clear about that.

Thanks,
- Divya.

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From: David Charlap <[email-masked]>
Date: Thu, 24 May 2001 15:48:20 -0400

> RSVP? RFC2205 is not very clear about that.

RSVP routers refresh their state on a timer.  This is the definition of
soft state.

If there is a loop, the router at the point where the path connects back
to itself may continue receiving refreshes from the router the loop is
coming from, even through the ingress has stopped refreshing the state. 
This leads to a circular topology where everybody is refreshing state
unnecessarily.

Section 3.4 of RFC 2205 describes what has been done in the protocol to
prevent these kinds of loops from happening.

Note, however, that with the TE extensions, looping should not happen in
the first place.  For a Path that has no ERO object, behavior is similar
to that of RFC 2205.  For a Path that has an ERO consisting entirely of
strict hops, any looping will be due to the ingress router deliberately
creating it - meaning the problem is with whatever entity generated that
ERO.  A Path with an ERO that has loose subobjects may loop, but this is
solved by using the RRO object - which is mandatory when a loose-ERO is
present.

-- David