you should know what it is... many posts about it below:
http://insearchofthecert.blogspot.com/#uds-search-results
dls1#sh ip cef
Prefix Next Hop Interface
0.0.0.0/0 192.168.1.1 FastEthernet0/24
0.0.0.0/32 receive
10.0.0.0/8 attached Null0
10.1.1.0/24 172.16.1.10 Vlan1
10.1.1.1/32 10.3.1.1 FastEthernet0/21
10.3.1.0/24 attached FastEthernet0/21
10.3.1.0/32 receive FastEthernet0/21
10.3.1.1/32 attached FastEthernet0/21
10.3.1.2/32 receive FastEthernet0/21
10.3.1.255/32 receive FastEthernet0/21
172.16.0.0/16 attached Null0
172.16.1.0/24 attached Vlan1
172.16.1.0/32 receive Vlan1
172.16.1.1/32 receive Vlan1
172.16.1.2/32 attached Vlan1
172.16.1.5/32 receive
172.16.1.10/32 attached Vlan1
172.16.1.101/32 attached Vlan1
172.16.1.102/32 attached Vlan1
172.16.1.255/32 receive Vlan1
--More--
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
