19

On one of my routers, I see the following switching modes:

#show fabric switching-mode 
Global switching mode is Truncated
dCEF mode is not enforced for system to operate
Fabric module is not  required for system to operate
Modules are allowed to operate in bus mode
Truncated mode is allowed, due to presence of DFC, CEF720, Standby supervisor module

Module Slot     Switching Mode
1                      Bus
2                 Crossbar
3                     dCEF
4                      Bus
5                      Bus
6                 Crossbar
7                      Bus
8                      Bus
9                 Crossbar

What is the difference between Crossbar, Bus, and dCEF switching modes?

19

"Bus" is connection to 16Gbit/s bus that is common to legacy 6500 architecture.

Crossbar and dCEF mean the connection from the LC (line card) is using switch fabric (separate SFM module for Sup2, integrated switch fabric chip on Sup720 and Sup2T).

Crossbar means the connection is from the line card that doesn't have distributed processing capabilities (no DFC on it, CFC is installed), while dCEF means there's distributed CEF mode running on line card using DFC.

8

Quick rule of thumb: dCEF > Crossbar > Bus

If you have a line card operating in bus mode, then your active supervisor will operate in bus mode as well. This can impact the performance of your 6500/7600.

You may want to look into the modules running in bus mode. Many of these modules have been EoL for some time and should probably be replaced. We recently also discovered that the Sup2T will also have issues with modules that use CEF256 which will cause them to run in bus mode (per Cisco internal document referenced when we opened a TAC case) even though they will run in crossbar mode with a Sup720.

3

Check out this page for the info you require, plus a list of references from the Cisco site;

http://null.53bits.co.uk/index.php?page=6500-7600-chassis-architecture

  • 2
    Hi javano, thanks for the answer. On SE sites, to prevent link rot, it's suggested that answers include more than just a link to another site. You can edit your answer to include more pertinent information. – Aaron May 8 '13 at 16:18

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