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Re: What IOS really does with commands (was Re: ISIS Problem. posted 03/31/2004
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There's a few of these gotcha's .
We'd enabled ospf fast hello's on some 7301's. We used 50ms hellos, with a 1 second dead time.
We expected it to be twitchy, but it worked well, ...


Untill I poped the flash card out of the router...
That caused the box to drop all the ospf adjacencies. due to a file system bug that hogs CPU for a little to long
It had always done this .. but you didn't know there was a problem until we configured the fast hellos.


Wes

Richard Dumoulin wrote:

Ouch !! How did you notice that. Is it demonstrable ?

--Richard

-----Mensaje original-----
De: McCallum, Robert [mailto:robert.mccallum@xxxxxxxx]
Enviado el: miircoles, 31 de marzo de 2004 17:33
Para: 'dburnett@xxxxxxxxxx'; Howard C. Berkowitz
CC: ccielab@xxxxxxxxxxxxxx
Asunto: RE: What IOS really does with commands (was Re: ISIS Problem.


Something for you all to note is that many routers and IOS versions when you do a wr mem you induce a 350ms Outage of traffic flowing through the box. Now some of you may say "big deal" but put a voice switch or a time Sensitive application and watch it die every time you save the config. Some IOS versions now only do this the first Time you save the config i.e. just after it is reloaded others still do it every time. Also changing the boot system commands induces the same delay (there is no way round this).

Robert McCallum
CCIE #8757 R&S
01415663448
07818002241



-----Original Message-----
From: dburnett@xxxxxxxxxx [mailto:dburnett@xxxxxxxxxx]
Sent: 31 March 2004 16:25
To: Howard C. Berkowitz
Cc: ccielab@xxxxxxxxxxxxxx
Subject: Re: What IOS really does with commands (was Re: ISIS Problem.


Where may someone find more information (as much as may be publicly available) about how IOS creates and stores the data structure that it modifies from entered keywords (aka commands)?

----- Original Message -----
From: "Howard C. Berkowitz" <hcb@xxxxxxxxxxxx>
To: <ccielab@xxxxxxxxxxxxxx>
Sent: Sunday, March 28, 2004 9:20 PM
Subject: What IOS really does with commands (was Re: ISIS Problem.




At 7:56 AM -0800 3/28/04, Joseph Rinehart wrote:


?Sometimes the router will slightly alter commands in the active
configuration when you enter them. I had this happen on an
access-list


last


week and it nearly drove me crazy at first.


Something worth knowing to anyone studying for CCIE, but rarely
spelled out specifically, is that the router doesn't just


record, or


even alter the commands when you enter them -- it


interprets them and


then throws them away. The earlier courses can give you the
impression that the commands are entered are stored


somewhere in RAM.


They are not.

On slower routers, did you ever notice the slight delay


before "show


running" displays? Show running is essentially a reverse


compiler or


formatted dump that goes throgh the data structures of the


router and


creates the configuration statements it thinks would have put the
router into the states reflected by the current values of the data
structures. The delay is due to the significant processing


involved


in recreating the statements.



I think this is what is happening, and you would need to


change it by


specifying Level-1 in the redistribution statement, I believe the
syntax


is


"redistribute isis 1 level-1-only metric 4"




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Subscription information may be found at:
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Please help support GroupStudy by purchasing your study materials from:
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