[nsp] MSFC2 128,000 route limitation

[Junichi Shimagami]

Hi Matt,

I am wondering how much memory you have installed on SUP2.  Could
you share this information with us?

-simagami


On Thu, 22 Aug 2002 18:24:01 -0400,
	"Matt Buford" <matt@overloaded.net> wrote:

> On Wed May 15 2002 - 07:53:32 EDT, Ian Cox wrote:
> 
> > The TCAM that holds the FIB table is capable of holding 256,000 entries.
> > Without unicast RPF checking turned on the maximum number of unicast
> > entries that can be held in the hardware FIB table is 244,000. The
> > remaining 12,000 entries are reserved for multicast routes. If unicast RPF
> > checking is enabled then the number of routes that are held in the TCAM is
> > halved.
> 
> > You can exceed the capacity of the hardware forwarding table, and the
> > consequences are that the routes that are not programmed into the TCAM
> that
> > holds the FIB table will be switched in software by the MSFC2 / RP.
> 
> I have apparently ran into this limitation, with much worse consequences
> (running Sup2/MSFC2 hybrid).  The supervisor CPU shot up to 100%, and all
> updates from the MSFC to the supervisor/PFC stopped.  This happened in both
> of a pair of redundant 6500s, bringing both down and leaving me unable to
> bring them back up with a full routing table.
> 
> Cisco TAC found bug cscdw89942, and said the internal notes recommend using
> the "set mls cef per-prefix-stats disable" to reduce the number of entries.
> 
> It appears that at this point the limitiation is not something to take
> lightly.  Reaching it (at least under Hybrid) apparently brings everything
> down.  There is no software yet available that fixes this, and the only
> workaround is to take measures to reduce your CEF table size (such as
> turning off per-prefix-stats).
> 
> For perspective, the routers that failed each see two BGP feeds of full
> Internet routes, as well as about 12 OSPF routes (each of which has 2 or 3
> paths to get there).  This doesn't seem like a particularly large number of
> routes to me, however it certainly passes the limit listed in the bug of
> 50,000 routes with dual paths.
> 
> Is there anywhere I can get a count of the actual current number of entries
> and/or space free, or is the only way to tell to show the cef table size and
> manually figure out if you need to multiply it if you have unicast RPF on,
> then make sure that is less than 244,000?  I want to go through all my 6500s
> and make sure I'm not about to hit the limit on any of them (some are hybrid
> and some are native).  The thought of  all my 6500s falling over at once and
> staying down because I reached the maximum limit on routes scares me
> greatly.
> 
> 
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