Which three statements are true about CEF? (Choose three.)
A.
The FIB table is derived from the IP routing table.
B.
The adjacent table is derived from the ARP table.
C.
CEF IP destination prefixes are stored in the TCAM table, from the least specific to the most specific entry.
D.
When the CEF TCAM table is full, packets are dropped.
E.
When the adjacency table is full, a CEF TCAM table entry points to the Layer 3 engine to redirect the adjacency.
F.
The FIB lookup is based on the Layer 3 destination address prefix (shortest match).
Very interesting, but the Answers C is also correct?
From the book
Implementing Cisco IP Switched Networks (SWITCH) Foundation Learning Guide
Paragraph: CEF Processing.
FIB: Derived from the IP routing table and arranged for maximum lookup throughput. CEF IP destination prefixes are stored in the TCAM table, from the most-specific to the least-specific entry. The FIB lookup is based on the Layer 3 destination address prefix (longest match), so it matches the structure of CEF entries within the TCAM. When the CEF TCAM table is full, a wildcard entry redirects frames to the Layer 3 engine. The FIB table is updated after each network change but only once and contains all known routes—there is no need to build a routecache by central processing initial packets from each data flow. Each change in the IP routing table triggers a similar change in the FIB table because it contains all next-hop addresses
associated with all destination networks.
Also, the answer D is interesting.
If there is not a wildcard entry in FIB, then packet is dropped. Only if a wildcard entry is present, then packet is forwarded to software L3 switching.
The answer F – is false. Because true is “longest match”
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No, C is incorrect, because as it says in your book “prefixes are stored … from the most-specific to the least-specific entry”…
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you are right Yerlan.
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