How Forwarding Decisions are Made
Forwarding decisions are made as follows:
• If the destination does not match an entry in the routing table, the packet is forwarded through the interface specified for the default route. If a default route has not been configured, the packet is discarded.
• If the destination matches a single entry in the routing table, the packet is forwarded through the interface associated with that route.
• If the destination matches more than one entry in the routing table, and the entries all have the same network prefix length, the packets for that destination are distributed among the interfaces associated with that route.
• If the destination matches more than one entry in the routing table, and the entries have different network prefix lengths, then the packet is forwarded out of the interface associated with the route that has the longer network prefix length.
For example, a packet destined for 192.168.32.1 arrives on an interface of a security appliance with the following routes in the routing table:
hostname# show route
R 192.168.32.0/24 [120/4] via 10.1.1.2 O 192.168.32.0/19 [110/229840] via 10.1.1.3
In this case, a packet destined to 192.168.32.1 is directed toward 10.1.1.2, because 192.168.32.1 falls within the 192.168.32.0/24 network. It also falls within the other route in the routing table, but the 192.168.32.0/24 has the longest prefix within the routing table (24 bits verses 19 bits). Longer prefixes are always preferred over shorter ones when forwarding a packet.
Continue reading here: Enabling the DHCP Server
Was this article helpful?