hardware-based cef

Answered Question
Sep 9th, 2008

hi every body!

do all the switches\routers which provide hard-based cef, use switch engine not the main processor for layer3 switching?

Which are the switches and routers which provide software -based cef? is main processor used for software-based cef?

thanks a lot and have a nice day!

I have this problem too.
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Correct Answer by Giuseppe Larosa about 8 years 2 months ago

Hello Sarah,

yes it is the main cpu that builds FIB and adjacency tables and this actually happens on all platforms because all messages like CDP, ARP, routing protocol messages are sent to the main CPU for process switching.

Hardware based CEF platforms can have additional resources like DFC in C6500 linecards that can store a complete copy of the CEF tables and are used by ASIC chips for forwarding. The same happens in the GSR linecards and on CRS.

In these distributed platforms the main cpu has the duty to build the CEF tables, to update them and to send a copy to all linecards or modules that use them.

In a ISR or other routers like c2600 the CEF tables are built by the main cpu and used by other sw processes running over it like IP input and so on.

Hope to help

Giuseppe

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Giuseppe Larosa Tue, 09/09/2008 - 10:46

Hello Sarah,

hardware based CEF is performed by multilayer switches including 6500, 4500, 3750.

some of this platform like 6500 can perform distributed hardware based CEF with the most recent linecards.

other devices that use hardware based CEF are GSR 12000 and CSR terarouters that use distributed hardware CEF.

An ISR 1800, 2800 is an example of a device that uses software based CEF so it is also for 7206VXR with every type of NPE.

I don't think there are switches that perform software based CEF: or they use CEF for multilayer switching or they are just L2 switches.

Hope to help

Giuseppe

sarahr202 Tue, 09/09/2008 - 11:46

thanks for your reply Giuseppe!You mentioned ISR 1800,2800 devices use software-based cef.

who builds FIB and adjacency table in software-based cef and where? is it Main processor that builds fib and adjacency table?

thanks a lot!

Correct Answer
Giuseppe Larosa Wed, 09/10/2008 - 00:32

Hello Sarah,

yes it is the main cpu that builds FIB and adjacency tables and this actually happens on all platforms because all messages like CDP, ARP, routing protocol messages are sent to the main CPU for process switching.

Hardware based CEF platforms can have additional resources like DFC in C6500 linecards that can store a complete copy of the CEF tables and are used by ASIC chips for forwarding. The same happens in the GSR linecards and on CRS.

In these distributed platforms the main cpu has the duty to build the CEF tables, to update them and to send a copy to all linecards or modules that use them.

In a ISR or other routers like c2600 the CEF tables are built by the main cpu and used by other sw processes running over it like IP input and so on.

Hope to help

Giuseppe

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