10.10.0.0/24 directly connected: Gi0/010.10.1.0/24 directly connected: Gi0/110.10.2.0/30 directly connected: Se0/0/00.0.0.0/0 via 10.10.2.2 (next-hop router)Each row in the routing table lists a destination network
and the corresponding interface or next-hop address. For
directly connected networks, the router has an interface
that is part of that network. For example, let’s assume
that a router receives a data packet on its
GigabitEthernet0/1 interface with destination IP address
10.10.0.15. The router looks up the destination address
in its routing table and decides to route the packet out its
GigabitEthernet0/0 interface toward the destination.
Following the same logic, let’s assume next that the
router receives a packet on its GigabitEthernet0/0
interface with destination IP address 172.16.0.25. The
router performs a routing table lookup and finds that it
doesn’t have an explicit route for that network, but it
does have a default route (0.0.0.0/0) via the next-hop
router with IP address 10.10.2.2. Looking up recursively
how to reach the 10.10.2.0 network, the router forwards
the packet out its Serial0/0/0 interface toward the next-
hop router, which should be closer to the destination.
Default routes on routers—much like the default gateway
configurations on end host devices—are used as a last
resort for routing any data packets for which the
destination doesn’t explicitly exist in the routing table.
Default routes are extremely helpful in maintaining a
small routing table and hence decreasing the routing
table lookups and also decreasing the amount of time
needed to decide on which interface to route the traffic,
leading to faster routing of data packets. For the majority
of routers, a full Internet routing table with hundreds of