[c-nsp] OIR in 6500/7600

[Ross Vandegrift]

On Mon, Nov 10, 2008 at 06:50:34PM +0200, Tassos Chatzithomaoglou wrote:
> Keep in mimd that DFC equipped modules do not have this problem. According 
> to Cisco:
> 
> "The addition of a DFC module effectively disconnects a module from the 
> Data Bus. As such, a DFC-enabled module is not subject to the bus stall 
> mechanism that occurs when a module is inserted or removed from the 
> chassis. Throughout these Online Insertion and Removal (OIR) events, the 
> Data Bus is temporarily paused for just enough time to ensure that the 
> insertion/removal process does not cause any data corruption on the 
> backplane. This protection mechanism causes a very brief amount of packet 
> loss (sub-second, but dependent on the time it takes to fully insert a 
> module). A module with a DFC onboard is not directly affected by this stall 
> mechanism and does not have any packet loss on OIR."

This is correct, but it can be complicated.  DFC enabled cards still
stall the bus, but since they fabric switch, they won't experience drops.
Be more careful if your chassis is running in mixed mode for fabric and
bus mode switching - in that case, you have some cards that do need
the bus (for example, the CSM).

I've OIRed lots of cards on production 6500s and never had a problem
with a bus-stall causing problems, even on systems that are
fabric-enabled and have to do some bus switching.

I agree with the previous poster that suggested not being afraid to
use a little bit of force to make sure they seat quickly :)  Of
course, don't use so much force that a caught cable gets snapped off...

This page from UCAR has pretty good descriptions of the bus and fabric
basics, as well as info on some of the bizarre names that Cisco uses to
refer to pieces that arbitrate backplane traffic:

http://www.cisl.ucar.edu/nets/devices/eswitches/6500-backplane.html

Ross

-- 
Ross Vandegrift
ross at kallisti.us

"If the fight gets hot, the songs get hotter.  If the going gets tough,
the songs get tougher."
	--Woody Guthrie