network cisco ccna gns3 certification arteq

network cisco ccna gns3 certification arteq
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Wednesday, July 4, 2012

ip cef...

cisco express forwarding...

you should know what it is... many posts about it below:

dls1#sh ip cef
Prefix               Next Hop             Interface            FastEthernet0/24           receive               attached             Null0          Vlan1             FastEthernet0/21          attached             FastEthernet0/21          receive              FastEthernet0/21          attached             FastEthernet0/21          receive              FastEthernet0/21        receive              FastEthernet0/21        attached             Null0        attached             Vlan1        receive              Vlan1        receive              Vlan1        attached             Vlan1        receive           attached             Vlan1      attached             Vlan1      attached             Vlan1      receive              Vlan1

note the above table... now read this: (from hucaby, ccnp switch, pg. 222

Basically, the routing table is reformatted into an ordered list with the most specific route first, for each IP destination subnet in the table. The new format is called a Forwarding Information Base (FIB) and contains routing or forwarding information that the network prefix can reference.

In the FIB, these would be ordered with the most specific, or longest match, first, followed by less specific sub-nets. When the switch receives a packet, it easily can examine the destination address and find the longest-match destination route entry in the FIB.

the longest matches are not ordered first according to the output... the longest match in any case would be a slash 32... they are found towards the end of each subnet entry represented in the table

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