[c-nsp] Sup720 Config registry

[Richard A Steenbergen]

On Sun, Aug 31, 2008 at 03:28:18PM +0200, Mikael Abrahamsson wrote:
> On Sun, 31 Aug 2008, Brett Clausenhauf wrote:
> 
> >Can anybody who might know advise? It would be very much appreciated..
> 
> I had a similar issue back in SXE days (2+ years ago) where the conf-reg 
> would get out of sync between modules on the Sup720-3bxl (it would show 
> conf-reg 0x2102 in IOS, but rebooting would go into rommon).
> 
> To fix it, I would simply do a conf-reg 0x2102 and "wr" in regular config 
> mode, which seemed to set this conf-reg on all modules, making the problem 
> go away.

I've seen a couple really cool side-effects from an out-of-sync config
register between RP and SP... For example, I was once rebooting a sup720 
to change the cef maximum-routes tcam partitioning, and as soon as it
would boot back up it would install a "reboot in 10 minutes" rule, 
like what Jared mentioned here:

http://puck.nether.net/pipermail/cisco-nsp/2006-October/035266.html

After sitting through a lot of automatic reboots and trying everything
known to man to stop them, I finally found the problem was a desynced
config-register that you couldn't see from IOS at all (you had to start
a shell on the SP to see it), which caused the SP to not process the
RP's new tcam partition config. Apparently there was some edge condition
which might need you to reboot twice to fully update the SP, so Cisco
just wrote code to automatically reboot if the SP wasn't updated
correctly. Combine that with an out-of-sync config-register and you've
got lots of endless rebooting fun. :)

-- 
Richard A Steenbergen <ras at e-gerbil.net>       http://www.e-gerbil.net/ras
GPG Key ID: 0xF8B12CBC (7535 7F59 8204 ED1F CC1C 53AF 4C41 5ECA F8B1 2CBC)