Subject: [Isis-wg] Hello Multiplier - FINAL ROUND

From: Jeff Parker <[email-masked]>
Date: Mon, 8 Apr 2002 14:50:30 -0400

While there is still discussion on some of the topics, I hope
we can close out a few of the more straight forward ones
such as Hello Multiplier.  If there is debate about this
or other "Final" rounds, we will keep them open until
rough consensus emerges.

I will circulate the current versions of all items, together
with a note about what has changed, and a list of any questions
open in my mind.  

- jeff parker

- Included historical note about original value in DECnet

5.2 Hello Multiplier

   An IS sends IS to IS Hello Protocol Data Units (IIHs) on a periodic
   basis over active circuits, allowing other attached routers to moni-
   tor their aliveness. The IIH includes a two byte field called the
   Holding Time which defines the time to live of an adjacency. If an IS
   does not receive a hello from an adjacent IS within this holding
   time, the adjacent IS is assumed to be no longer operational, and the
   adjacency is removed.

   [ten] states that the value of Holding Time  should be ISISHolding-
   Multiplier multiplied by iSISHelloTimer for ordinary systems, and
   dRISISHelloTimer for a DIS, and sets ISISHoldingMultiplier to a value
   of 10. This implies that the neighbor must lose 10 IIHs before an
   adjacency times out.

   In practice, a value of 10 for the ISISHoldingMultiplier has proven
   to be too large. Most implementations set the default ISISHoldingMul-
   tiplier to 3, the original value in DECnet PhaseV, and allow the net-
   work operator to configure it. Note that the Holding Timer may be
   asymmetric among the routers on the same link.

   Thus Hello Multiplier may be a configurable administrative parameter,
   with values between 3 and 10. Values lower than 3 are less stable,
   and may cause adjacencies to flap.
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From: Jeff Learman <[email-masked]>
Date: Mon, 08 Apr 2002 16:04:04 -0400

Trivial edit suggestion below.  Keep or toss, no reply necessary.

>   asymmetric among the routers on the same link.

... the Holding Timer need not be set consistently among the routers ...