[c-nsp] IS-IS Emergency

Vinny Abello vinny at tellurian.com
Fri Jun 22 11:17:54 EDT 2007


Justin Shore wrote:
> Robert Boyle wrote:
>> At 02:40 PM 6/20/2007, you wrote:
>>> That brings up a related question.  Does anyone have any recommendations
>>> for using the overload-bit with a startup delay or BGP hold?  We set it
>>> to 5 minutes on boot.  I figure that's just enough time for the BGP to
>>> settle down.  These 720-3BXLs are in an iBGP mesh with both border
>>> routers and get a full Internet table from both.  The RIB Update and BGP
>>> Scanner processes don't usually settle down for 3-4 minutes.  Should I
>>> set a hard timeframe or should I just set it up to wait for BGP?
>> This is what we use on our Cisco & Foundry core network. This is 
>> obviously a Cisco config snippet.
>>
>> router isis
>>  net xxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>>  is-type level-2-only
>>  domain-password xxxxxxxxxxxxxxxx
>>  metric-style wide
>>  ip fast-convergence
>>  set-overload-bit on-startup wait-for-bgp
>>  max-lsp-lifetime 65535
>>  lsp-refresh-interval 65000
>>  no hello padding
>>  log-adjacency-changes
>>  passive-interface Loopback0
>>  maximum-paths 6
>>
>> It works very well and we don't have any issues.
> 
> Many thanks for the input, Robert.  That's close to what we're doing as 
> well.  We also have the prc-interval set to 10, increased 
> max-area-addresses and set NSF to cisco (plus some evil redistribution 
> that is temporary and will be gone soon).  "ip fast-convergence" isn't 
> an option on our 7600s.  What platform are you working on?  I'm going to 
> change up for "on-startup 300" to wait-for-bgp.  We upgraded to SRB1 
> last night and the overload-bit delay worked flawlessly.  The load on 
> the Sup pulling down 2 full BGP tables from directly connected routers 
> took less than 30 seconds, the RIB update was finished in well under a 
> minute, and the load never exceeded 30%.  This is compared to the load 
> pegging at 100% for a couple minutes without the delay.  Much better.  :-)

Just a side note as well:

As far as the BGP convergence on start-up, you may also want to
investigate using "ip tcp path-mtu-discovery" in your configurations if
you don't have it already. Last I knew, the MTU defaults to a very low
size for BGP sessions. Adding this command will allow it to converge
faster as more data can be transmitted in each packet when your sessions
are coming up.

Our ISIS configuration above that Robert provided was largely based on
the recommended settings from Cisco that were provided to AOL during
their OSPF to ISIS migration... maybe minus the ip fast-convergence.

Our (Cisco) platforms are generally Cat6500 12.2(18)SXF and 7206
12.2(28)SB builds.

-- 

Vinny Abello
Network Engineer
vinny at tellurian.com
(973)940-6100
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