From: William Nellis (nellis_iv@yahoo.com)
Date: Tue Nov 06 2007 - 02:21:45 ART
EEM scripting is great for doing a number of things. 2 things, though,
1) Use at your own risk. Cisco can't validate and regression test every permutation or script. If you tell the router to reboot every time you enter configuration mode... have a blast. They put power switches on the routers, you assume liability for using them...
2) Using them as a solution like this in CCIE lab is probably not going to get you the points for the problem. It may be a good solution, but they are looking for you to solve the problem a certain way using keywords to guide solutions in manner which can be supported (see above number 1 for reason not all eem would be supported... The eem process is supported by Tac, homegrown eem scripts... not so much :) )
I have used EEM for a few good purposes mainly
1) rapid isolation of transient issue to collect data during transient condition (saved WEEKS of Troubleshooting)
2) Delay ospf timers for withdraw on CSM failover (so active CSM advertised via RHI into OSPF before the old LSA got maxaged... preventing BGP withdraw and associated 30 update timer delay for readvertisement)
3) in lab testing to constantly break/fix/break/fix repeat, the network to ensure convergence keeps happening and routers dont eventually barf.
They can solve a huge amount of challenges in the control plane if you need a solution for something that isn't native to IOS. They are to routers what route-maps are to routes. But... You break it... you bought it :)
-------------------------------------------------------
r/s
William Nellis IV
nellis_iv@yahoo.com
----- Original Message ----
From: Ajay Prakash <ajay.prakash@networkpeople.co.in>
To: Joseph Brunner <joe@affirmedsystems.com>; Eric Phillips <ephillips@squick.cc>; ccielab@groupstudy.com
Sent: Monday, November 5, 2007 8:15:31 PM
Subject: RE: Any way to force OSPF DR other than "priority 0"?
Hello Joseph,
Could you please share the script as you mentioned. It would be great to
learn something like this. I would also appreciate if you could share some
link on scripting for routers.
Ajay
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Joseph Brunner
Sent: Monday, November 05, 2007 11:31 PM
To: 'Eric Phillips'; ccielab@groupstudy.com
Subject: RE: Any way to force OSPF DR other than "priority 0"?
As you know the DR is not preempt-able
I could do this with EEM;
Basically script up an applet that restarts the ospf process on a router
that receives a new neighbor adj = router 1. If router 2 and 3 are running
this applet, and they clear their neighbor adjacency, 1 will be the dr on
the wire when the restart.
That touches the config on R2 & R3, but does not touch priority from default
of 1. OF course I would demand 5 points from the proctor's for being a
little hacker and doing this... LOL
Would you like to see it?
-Joe
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of Eric
Phillips
Sent: Monday, November 05, 2007 12:05 PM
To: ccielab@groupstudy.com
Subject: Any way to force OSPF DR other than "priority 0"?
Hey all,
I have done quite a bit of Googling and DOC-CD reading, and have not found
anyone offering any clever ways to force the election of a certain router as
the DR besides setting the priority to 0 on all other routers.
For example, if I had a question that asked me to ensure Router1 was always
the DR on a certain segment without touching the configuration of Router2
and Router3 I can set the priority very high on Router1, but if Router1
boots a few seconds later than Router2, Router2 will be the DR even if it
has it's default priority of 1. The only way I can think to completely
guarantee Router1 is always the DR is to make the priority 0 on all other
routers.
Am I missing something obvious, or am I over thinking this too much? I have
not seen this asked in any practice labs, just theorizing what could happen.
-Eric
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