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Bronze

CEF and Fast switching on same int

How does this work if both CEF and Fast switching are both enabled on the same interface? How does it know to use CEF?

sh ip int:

FastEthernetx/x is up, line protocol is up

IP fast switching is enabled

IP fast switching on the same interface is disabled

IP Flow switching is disabled

IP CEF switching is enabled

IP Feature Fast switching turbo vector

IP Feature CEF switching turbo vector

IP multicast fast switching is disabled

IP multicast distributed fast switching is disabled

IP route-cache flags are Fast, CEF

-TIA

1 ACCEPTED SOLUTION

Accepted Solutions
Gold

Re: CEF and Fast switching on same int

CEF will attempt to switch the packet first, and if it cannot, it will "punt" the packet to the next slower switching path, in this case fast switching. It's just the way the code is written--the switching vector associated with an interface is a list of sorts, and hardware is always first on that list, followed by CEF, then followed by fast, and then other methods....

http://www.cisco.com/en/US/products/sw/iosswrel/ps1831/products_configuration_guide_chapter09186a00800ca6c9.html

Look for punt.

:-)

Russ.W

2 REPLIES
Cisco Employee

Re: CEF and Fast switching on same int

CEF is the primary switching path when enabled on an interface.

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México 
Paseo de la Reforma 222 Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
Gold

Re: CEF and Fast switching on same int

CEF will attempt to switch the packet first, and if it cannot, it will "punt" the packet to the next slower switching path, in this case fast switching. It's just the way the code is written--the switching vector associated with an interface is a list of sorts, and hardware is always first on that list, followed by CEF, then followed by fast, and then other methods....

http://www.cisco.com/en/US/products/sw/iosswrel/ps1831/products_configuration_guide_chapter09186a00800ca6c9.html

Look for punt.

:-)

Russ.W

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