Switching+Paths

Optimizing the forwarding process inside routers

=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