Mitesh,
Let me give it a try:
isco Express Forwarding (CEF) switching is a proprietary form of scalable switching intended to tackle the problems associated with demand caching. With CEF switching, the information which is conventionally stored in a route cache is split up over several data structures. The CEF code is able to maintain these data structures in the Gigabit Route Processor (GRP), and also in slave processors such as the line cards in the 12000 routers. The data structures that provide optimized lookup for efficient packet forwarding include:
- The Forwarding Information Base (FIB) table - CEF uses a FIB to make IP destination prefix-based switching decisions. The FIB is conceptually similar to a routing table or information base. It maintains a mirror image of the forwarding information contained in the IP routing table. When routing or topology changes occur in the network, the IP routing table is updated, and these changes are reflected in the FIB. The FIB maintains next-hop address information based on the information in the IP routing table.
Because there is a one-to-one correlation between FIB entries and routing table entries, the FIB contains all known routes and eliminates the need for route cache maintenance that is associated with switching paths such as fast switching and optimum switching.
- Adjacency table - Nodes in the network are said to be adjacent if they can reach each other with a single hop across a link layer. In addition to the FIB, CEF uses adjacency tables to prepend Layer 2 addressing information. The adjacency table maintains Layer 2 next-hop addresses for all FIB entries.
1. CAM table records the incoming packet's MAC address, Port & VLAN.to enable Switching at Layer 2.
2. The Adjacency table records IP address and Layer 2 header for the IP and then references the TCAM table and at this point the switch will have enough information to rewrite the packets headers and send them out the egress port..... The idea is that all of the information is loaded into the Adjacency table & TCAM table as these are run on the ASIC's which makes it hardware/wire speed Layer 3/MLS switching.
Now coming to reality:
C6K1#show adjacency
Protocol Interface Address
IP GigabitEthernet5/2 10.104.149.1(7)
IP Vlan10 10.10.10.2(10)
C6K1#sh ip arp 10.10.10.2
Protocol Address Age (min) Hardware Addr Type Interface
Internet 10.10.10.2 16 0026.9809.7dc1 ARPA Vlan10
C6K1#sh mac address-table address 0026.9809.7dc1
Legend: * - primary entry
age - seconds since last seen
n/a - not available
vlan mac address type learn age ports
------+----------------+--------+-----+----------+--------------------------
Module 1:
* 201 0026.9809.7dc1 dynamic Yes 0 Po100
* 10 0026.9809.7dc1 dynamic Yes 0 Po100
Module 4:
* 50 0026.9809.7dc1 dynamic Yes 0 Gi4/6 >>> Mac address and port is seen here.
* 1 0026.9809.7dc1 dynamic Yes 0 Gi4/6
HTH
