From: Andrew Lissitz \(alissitz\) (alissitz@cisco.com)
Date: Sat Oct 08 2005 - 15:07:58 GMT-3
Hello Simon and GS,
CEF has been around for quite a while, since 11.3 on some platforms. It
was not until 12.0 that CEF really started to replace fast switching on
most platforms. Here is a IOS 12.0 (purposely outdated link ...) link
that discusses CEF, CEF punts, and less desirable switching technologies
(a very quick read). Watch the word wrap ;-)
http://www.cisco.com/en/US/products/sw/iosswrel/ps1828/products_tech_not
e09186a00801e1e46.shtml
So before CEF, and when CEF is disabled, we have fast switching. The
additional option 'policy' was added in 12.0 code. This option was
added to the ip route-cache command because PBR used to kill the CPU due
to process switching. Thankfully after 12.0 something (I do not know
which version of 12.0) PBR was also fast switched. With CEF PBR is
cached
Here is a good link that discusses CEF, what happens when you disable
CEF and the policy option:
http://www.cisco.com/en/US/products/sw/iosswrel/ps1835/products_command_
reference_chapter09186a0080086f2a.html#wp1079617
On a side note:
I am not sure anyone in GS has dealt with Expand, Peribit, Pacteteer
etc... But these companies will sometimes ask you to place their
products off of a switch or router port. You can then use PBR to direct
TCP, Citrix, grennscreen, or whatever
kind of traffic to these devices and gain from TCP optimization and
compression services run on these devises. PBR is a
good option for directing traffic to these devices since there is not a
performance hit on the router.
On another side note ... side note:
Why disable CEF? If you find it buggy or your code does not support it
... Get new code! CEF is mandatory for many features and needs to be
enabled or working correctly in your network.
Take care group,
Andrew
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
simon hart
Sent: Saturday, October 08, 2005 1:07 PM
To: Andrew Lissitz (alissitz); Private Ryan; Cisco certification
Subject: RE: route-map ip next-hop
Andrew,
Yes you are right if CEF is enabled. However if CEF is disabled then I
believe policy routing is process switched unless the command ip
route-cache policy is configured on the interface.
Simon
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
Andrew Lissitz (alissitz)
Sent: 08 October 2005 16:30
To: simon hart; Private Ryan; Cisco certification
Subject: RE: route-map ip next-hop
Hello All,
Simon what you described was pre IOS 12.0 behavior... all packets are
fast / cef switched now, even with PBR. For more info, do a search for
the ip route-cache command
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
simon hart
Sent: Saturday, October 08, 2005 10:09 AM
To: Private Ryan; Cisco certification
Subject: RE: route-map ip next-hop
No need to turn off ip route-cache. By virtue of the fact that you put
the ip policy onto the interface I believe that all packets will be
processed switched anyway.
Simon
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
Private Ryan
Sent: 08 October 2005 14:29
To: Cisco certification
Subject: route-map ip next-hop
Hi Group
If I setup "policy route-map" to hardcode the ip next-hop, is it nessary
to disable "ip route-cache" for the incoming interface ?
Ryan
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