Subject: Re: Is HoldingMultiplier=10 a good value?

From: Tony Li <[email-masked]>
Date: Thu, 29 Apr 1999 01:09:41 -0700 (PDT)

From: Mike Shand <[email-masked]>

At 07:43 29/04/99 +0100, Peter Higginson wrote:
>
>Holding Multiplier has been a per-circuit variable ever since the
>original 1994 draft of the IS-IS MIB.

Yes, it should definitely be a variable (and is in all the implementations
I know about). What the default should be is somewhat debatable. If you
recall, the DEC spec had Pt-Pt as 3 * 10 seconds, and LANs as 10 * 3
seconds, so they both took 30 seconds to time out, but the LANs used a LOT
more bandwidth (especially since the LAN hellos are padded). That
distinction between LANs and Pt-Pt is now an anachronism, since Pt-Pt
circuits may have more available bandwidth than many LANs, and (as Peter
points out) don't tend to run 'reliable' data link protocols (although the
overall reliability is probably high). Given that different customers have
different requirements for stability v rapid failure detection, it all
leads to the conclusion that a universal 'default' is elusive.

I see no reason to change the current defaults. The important thing is that
they can be set to useful values if people care.

As Tony says, there is no NEED to use the holding time = hello time *
holding multiplier concept. The ratio between the hello time and the
holding time defines it anyway, and would permit non-integral values for
the notional 'multiplier'. Indeed, it is generally good practice to use a
multiplier slightly larger than an integer (well alright Tony, a holding
time slightly larger than an integer number of hello times - not QUITE the
same thing), although the effect of jitter is to make MOST of the hellos
come early anyway.

So if we were re-writing the spec (which we aren't) we'd just specify the
hello time and the holding time in the protocol part, and leave it up to
the MIB to decide how those were presented to management. AS long as it
prevented the foot shooting of making holding time shorter than hello time,
I don't care what it says technically, but it would probably be better to
stick with what people know now.

>
>I'm personnally in favour of making the default 10 to be more
>conservative than the current (MIB) default of 3. As I remember
>it, the DEC (DNA) default is 10 on LANs and 3 on Pt-to-Pt circuits
>(which were assumed to have a reliable link layer).
>
>Peter
>
>At 19:32 28/04/99 -0400, Radia Perlman - Boston Center for Networking wrote:
>>I was just looking at the 10589 spec and realized that not only is
>>HoldingMultiplier specified to be a constant, but it's the value 10.
>>That seems excessively large. It would take a long time to notice
>>someone has gone down.
>>
>>I would have expected HoldingMultiplier to be a parameter, or having
>>HoldingTime a parameter in addition to HelloTimer. But it's nice to
>>have fewer parameters, but in that case I'd have assumed it would be
>>something like 3 or 4, not 10.
>>
>>Of course since the only thing you report is HoldingTime, it would
>>be completely compatible if a router used a different HoldingMultiplier.
>>
>

---

From: "Fu, James" <[email-masked]>
Date: Thu, 29 Apr 1999 07:20:12 -0400

Holding Mutiplier is a configurable parameter. Therefore, I have control of
it when I bring up networks.

As for the default value,  anything between 1 to 10  will be reasonable.  

James Fu
[email-masked]
http://www.netcoresys.com/
Netcore System Inc.
187 Ballardvale Street
Wilmington, MA 01887
(978) 694-1555 ext. 252 

> -----Original Message-----
> From:	Peter Higginson [SMTP:[email-masked]]
> Sent:	Thursday, April 29, 1999 2:43 AM
> To:	Radia Perlman - Boston Center for Networking; [email-masked]
> Subject:	Re: Is HoldingMultiplier=10 a good value?
> 
>

---

From: Jeff Parker <[email-masked]>
Date: Thu, 29 Apr 1999 09:32:48 -0400

I have submitted version .01 of the MIB, and expect to see it on the
list
shortly.  It includes per-circuit and per-level values of the Hello
Timer and 
Multiplier, with the following defaults.  Peter has suggested that we
change
the values of (10 seconds x 3) to (3 seconds x 10) in the next draft.  

The granularity has been changed to milliseconds from seconds.  
As always, implementations of a MIB may not be able to take on 
all possible settings.  

The text is also pretty normative about how to derive the holding time
from 
the MIB values.  

Comments and suggestions are always welcome: if there seems
to be a need, I may have time to rev the MIB again before Oslo.

- jeff parker

    isisCircL1HelloTimer OBJECT-TYPE
        SYNTAX Integer32 (10..600000)
        MAX-ACCESS read-write
        STATUS current
        DESCRIPTION
            "Maximum period, in milliseconds, between Level 1
            IIH PDUs on multiaccess networks.  It is also used
            as the period between ISH PDUs when polling the ES
            configuration, and the period between Hellos on point
            to point circuits. This object follows the resettingTimer
            behaviour."
        REFERENCE "{ISIS.aoi iSISHelloTimer (45)}"
        DEFVAL { 10000 }
    ::= { isisCircEntry 34 }

    isisCircL2HelloTimer OBJECT-TYPE
        SYNTAX Integer32 (10..600000)
        MAX-ACCESS read-write
        STATUS current
        DESCRIPTION
            "Maximum period, in milliseconds, between Level 1
            IIH PDUs on multiaccess networks.  This object
            follows the resettingTimer behaviour."
        REFERENCE "{ISIS.aoi iSISHelloTimer (45)}"
        DEFVAL { 10000 }
    ::= { isisCircEntry 35 }

    isisCircL1HelloMultiplier OBJECT-TYPE
        SYNTAX Integer32 (2..100)
        MAX-ACCESS read-write
        STATUS current
        DESCRIPTION
            "This value is multiplied by the corresponding HelloTimer
            and the result in seconds (rounded up) is used as the
            holding time in transmitted hellos, to be used by receivers
            of hello packets from this IS"
        REFERENCE "{ISIS.aoi iSISHelloTimer (45)}"
        DEFVAL { 3 }
    ::= { isisCircEntry 36 }

    isisCircL2HelloMultiplier OBJECT-TYPE
        SYNTAX Integer32 (2..100)
        MAX-ACCESS read-write
        STATUS current
        DESCRIPTION
            "This value is multiplied by the corresponding HelloTimer
            and the result in seconds (rounded up) is used as the
            holding time in transmitted hellos, to be used by receivers
            of hello packets from this IS"
        REFERENCE "{ISIS.aoi iSISHelloTimer (45)}"
        DEFVAL { 3 }
    ::= { isisCircEntry 37 }

- jparker
- nexabit.com

> From:	Tony Li [SMTP:[email-masked]]
> Sent:	Thursday, April 29, 1999 4:10 AM
> To:	[email-masked]