From: Landon Fitts (l.fitts@xxxxxxxxxxxxxx)
Date: Thu Apr 25 2002 - 15:12:53 GMT-3
Guy,
In the way that I understand the router to "process" an incoming packet,
is that if congestion occurs at the outgoing interface, the queuing
technique in place will occur irregardless of whether you are doing
process-switching or fast-switching (I know I will be corrected if my
understanding is wrong).
When a packet enters the router interface, the router says do I "process"
switch this packet or "fast-switch" it. If it is process switched the
packet will go through the normal route process. If fast-switched the
packet will be "switched" to the outgoing interface based on the information
in the "route-cache". The one thing that I am curious about is that I
thought if you apply an access-list to an interface, that forces the router
to process-switch
on that interface by default. So, when you didn't get any debug messages or
hits for your ACL that confused me a little. Was your ACL applied to an
interface or did you just set up an ACL globally so you could see hits?
One last thing is that even if you have fast-switching enabled on an
interface the first packet to a particular destination will be
process-switched to build the cache, and then subsequent packets will be
fast-switched.
HTH
Regards,
Landon Fitts
CCNP, CCDP, NNCSE, NNCDE
l.fitts@mindspring.com
----- Original Message -----
From: "Lupi, Guy" <Guy.Lupi@eurekaggn.com>
To: "'Landon Fitts'" <l.fitts@mindspring.com>; <ccielab@groupstudy.com>
Sent: Thursday, April 25, 2002 1:39 PM
Subject: RE: ip route-cache
> Thanks for that link. Now my question is, since I had to turn off ip
route
> cache to see the debugging output and the hits on the ACL, was the
priority
> queueing working with ip route cache turned on? I imagine that it was,
> since I have never seen a reference that states you have to turn route
> caching off when using it.
>
> ~-----Original Message-----
> ~From: Landon Fitts [mailto:l.fitts@mindspring.com]
> ~Sent: Wednesday, April 24, 2002 11:07 PM
> ~To: Lupi, Guy; ccielab@groupstudy.com
> ~Subject: Re: ip route-cache
> ~
> ~
> ~Guys,
> ~
> ~Here is an excerpt from cco -
> ~http://www.cisco.com/univercd/cc/td/doc/product/software/ios122
> ~/122cgcr/fswt
> ~ch_c/swprt1/xcfipsp.htm#xtocid7
> ~(watch the word wrap)
> ~
> ~For some diagnostics, such as debugging and packet-level
> ~tracing, you will
> ~need to disable fast switching. If fast switching is running,
> ~you will not
> ~see packets unless they pass through the Route Processor (RP).
> ~Packets would
> ~otherwise be switched on the interface. You might want to turn off fast
> ~switching temporarily and bypass the RP while you are trying to capture
> ~information.
> ~
> ~Regards,
> ~
> ~Landon Fitts
> ~CCNP, CCDP, NNCSE, NNCDE
> ~l.fitts@mindspring.com
> ~
> ~----- Original Message -----
> ~From: "Lupi, Guy" <Guy.Lupi@eurekaggn.com>
> ~To: <ccielab@groupstudy.com>
> ~Sent: Wednesday, April 24, 2002 9:24 PM
> ~Subject: ip route-cache
> ~
> ~
> ~> I have noticed on several occasions that on my 2500 series
> ~routers, I will
> ~> try to set up priority or custom queueing and turn on
> ~debugging and find
> ~> that it is not working. Then I go to the interface and use
> ~the "no ip
> ~> route-cache" command, and all of the sudden I see the debug
> ~outputs and
> ~the
> ~> access list for the queueing taking hits. I have found that
> ~I only need
> ~to
> ~> do this on the 2500's, and not on the 2600's. Does anyone
> ~know of a link
> ~> that explains when and why one should turn off ip route-cache? I
> ~understand
> ~> that it disables fast switching and enables process switching, I just
> ~don't
> ~> know exactly when to use it. Thanks.
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