From: אלי קושרובסקי (eli_kosh@netvision.net.il)
Date: Mon Dec 25 2006 - 19:16:39 ART
Hi,
You understand the concept behind CEF, and behind fast switching as well.
One difference between them is that in fastswitching every first packet that
is about to be switched for every flow is proccess switched, while in CEF
the FIB and adjacency is pre build thus even the First packet at every flow
is CEF switched.
Second difference is: The CEF is actually what tells the ASIC's in the more
advanced platforms (GSR,CRS-1, 6500/7600)how to hardware switch the packet.
After the FIB is built it is downloaded to the Line Cards / Modules /
ASIC's. And the packets are hardware switched. I think it also what happens
in the new ISR's (X8XX Series).
If you will issue a command "ip route-cache flow" under an interface, after
that you will issue "sh ip cache flow"
You will be able to the route-cache which is the equavivalent of FIB for
fastswitching.
Hope it was of some help.
Eli
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Stefan Grey
Sent: Monday, December 25, 2006 6:10 PM
To: ccielab@groupstudy.com
Subject: CEF vs fast switching.
Guys could you please help me with understanding the following.
1) I want to understand how different switching methods function: especially
CEF, fastswitching, process Swithcing.
I have read several articles about CEF... but still don't fully understand
how does it function. And what I don't understand most and want to
understand most... Why CEF is more efficient than fast switching and other
switching methods???
1) Aboud CEF. Is my understanding correct as below???
As I understand CEF works as follows: It has FIB and adjacency table. Once
router or Layer 3 receives an IP packet it looks into FIB to determine the
next hop router. Next it looks in the adjacency table to match the next-hop
IP address with its MAC address and the output interface.. Than it does the
switching... Correct??? Please comment...
2) I have read about Fast switching that it makes switching first based on
process switching and than it build some route cache... and than switches
based on this cache.... But I don't understand it completely... Could you
plese explain how it works and how does this route cache look like???
Well I would appreciate any explanations... and also links where to read
more detail about this.
Thank you very much.
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