It could be that the author wants to implant "keep timer values consistent
across your network or die a horrible death" into the reader's head. So he
lists these timers. Maybe OSPF wants even the most trivial timers to match.
I don't recall these timers you speak of being in the hello packets, so the
routers will form adjacencies even if these timers don't match. I don't see
why these timers must match either, so im going to say the author just made
that assumption, and didn't want to confuse readers by saying "match these
timers up, and you dont have to worry about these timers", rather "keep all
timers consistent, and you'll be fine.
Richard A. Holland
Voice/Data Integrator
Telec, Inc.
http://www.telecinc.com
CCDA,CCNP,MCSE,CSE
-----Original Message-----
From: [EMAIL PROTECTED] <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED] <[EMAIL PROTECTED]>
Date: Thursday, September 14, 2000 8:04 PM
Subject: SPF timers
>
>
>At
http://www.cisco.com/cpress/cc/td/cpress/design/ospf/on0407.htm#xtocid163652
3
>(which is an extracted chapter from 'OSPF Network Design Solutions', by Tom
>Thomas), there is a bit that states...
>
>"Cisco's OSPF implementation enables you to alter certain
interface-specific
>OSPF parameters, as needed. You are not required to alter any of these
>parameters, but some interface parameters must be consistent across all
routers
>in an attached network. Those are the parameters set by the following
commands:
>
>ip ospf hello-interval
>ip ospf dead-interval
>ip ospf authentication-key
>timers spf spf-delay spf-holdtime
>
>Therefore, be sure that if you do configure any of these parameters, the
>configurations for all routers on your network have compatible values. "
>
>The first three I can understand, and I don't have a problem with these
>parameters having to match on all routers on the network. But I can't see
why
>the spf timers should have to match. And in any case, that one's not an
>interface-specific parameter.
>
>For those who haven't used this command before, 'spf-delay' is the delay
time,
>in seconds, between when OSPF receives a topology change and when it starts
a
>SPF calculation. 'spf-holdtime' is the minimum time, in seconds, between
two
>consecutive SPF calculations. The command reference on CCO doesn't mention
that
>the spf timers have to match on all routers. I can see that if they are
>mismatched by too much, it will take longer for routers to converge to a
>consistent view of the network, but would it cause any other problems?
>
>I've had a look at RFC 2328, and am no wiser, although I will happily admit
I
>did not read all 240 pages. Why would one router care how long another
router
>has waited between SPF calculations? Or is this an error in the
book/website -
>can they in fact be different everywhere (obviously it's simpler if they're
the
>same, but does it do nasty things to OSPF if they're not)?
>
>JMcL
>
>
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