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james_wright
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CEF

Sun Aug 19, 2012 1:10 pm

What is the purpose of the routing table, except to populate the FIB table in CEF? As I understand it, CEF forwards the packets, and routers only consult the FIB-ADJ table and not the routing table? Can someone clarify?

Thank you very much

James

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Re: CEF

Sun Aug 19, 2012 1:32 pm

yes, if cef is turned on your routing table will populate by routing protocol, connected routes, static routes that makes the routing decisions. CEF will switch the packets out of the correct interface.
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Re: CEF

Sun Aug 19, 2012 2:00 pm

Think of the RIB as part of the control plane while CEF (FIB) is part of the data plane.

In big routers there is proper separation between the 2

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Re: CEF

Sun Aug 19, 2012 4:16 pm

Also, CEF may is not used with certain packets such as the ones below.


"• Packets that use IP header options
• Packets that have an expiring IP time-to-live (TTL) counter
• Packets that are forwarded to a tunnel interface
• Packets that arrive with non-supported encapsulation types
• Packets that are routed to an interface with non-supported encapsulation types
• Packets that exceed the MTU of an output interface and must be fragmented
• Packets that require an IGMP redirect to be routed
• 802.3 Ethernet packets"

Therefore, RIB is not completely useless in terms of the forwarding function of a router.

james_wright
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Re: CEF

Tue Sep 04, 2012 3:50 am

Thank you very much.

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