[c-nsp] Catalyst 6500 Supervisor Engine Redundancy

[Jared Mauch]

On Mon, Oct 30, 2006 at 05:05:06PM +0000, Sam Stickland wrote:
> Lasher, Donn wrote:
> > I would only offer one caveat as to Redundancy mode discussions.
> >
> > For software-related failures, SSO may actually hurt you more than it
> > helps.
> >
> > SSO, at least in my experience in the past (was SRM as I recall), is a
> > complete "mirror" of one proc to the other. This means any memory
> > corruption issues, stack problems, IOS issues, that may cause the first
> > Proc to crash, may then crash the other proc as well, leading to a
> > chassis reboot. Badness.
> >
> > RPR+, while taking longer to fail over compared to SSO, avoids those
> > issues, by being "warm" but not "hot" standby.
> >
> > For hardware related failures on the other hand, SSO > RPR*
> >   
> Can anyone else offer any thoughts on this subject? From our prespective 
> we hardly ever see any supervisors fail (linecards are of course a 
> different story), but quite a lot of software related crashes, so it 
> sounds like SSO isn't a great solution from _our_ prespective (YMMV).
> 
> The described "double failure" mechanism above certainly sounds 
> plausible - has anyone got any real-world experience of it?

	there are a number of cases where this has been a problem
in the past.

	If you don't need IPv6 or MPLS currently, you should really
be running one of the modular versions of software on the
65xx/76xx (aka "76k").  This will help mitigate the risk from this
in providing you 1) core files and 2) significantly reduced risk of
a catastrophic SW failure causing you to POST all your hardware again.

	It doesn't reduce the "same bug, both RPs" risk, but will reduce
the downtime as just the iprouting process may restart, and not
the full image.  (same goes for udp.proc and tcp.proc).

	You can also recover from various failures without a reload.

	here's hoping to a soon release of the IPv6+MPLS related
software!

	- jared


-- 
Jared Mauch  | pgp key available via finger from jared at puck.nether.net
clue++;      | http://puck.nether.net/~jared/  My statements are only mine.