Optimizing the forwarding process inside routers
Checks FCS
Checks Ethernet Type field and extracts Packet
Checks routing table
Updates TTL field and Checksum
Encapsulates in new DataLink header and FCS
First packet is generated and destination and next hop information is cached in the fast-switching table (route cache).
Cached entries timeout out quickly
First packet must be process switched
Load balancing can only occur per destination
Forward Information Base (FIB) - loads entries as routes are added and removed from the routing table
FIB structure is special kind of tree known as "mtrie" and point to CEF adjacency table which lists outgoing interface and information for data link header.
config# ip cef
config-if# no ip route-cache cef
Process Switching
Checks FCS
Checks Ethernet Type field and extracts Packet
Checks routing table
Updates TTL field and Checksum
Encapsulates in new DataLink header and FCS
Fast Switching
First packet is generated and destination and next hop information is cached in the fast-switching table (route cache).
Cached entries timeout out quickly
First packet must be process switched
Load balancing can only occur per destination
Cisco Express Forwarding (CEF)
Forward Information Base (FIB) - loads entries as routes are added and removed from the routing table
FIB structure is special kind of tree known as "mtrie" and point to CEF adjacency table which lists outgoing interface and information for data link header.
config# ip cef
config-if# no ip route-cache cef
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