A next hop is the address of the device that will process the packet next. For a host on a network, the address of the default gateway (router interface) is the next hop for all packets that must be sent to another network. In the routing table of a router, each route to a remote network lists a next hop.
When a packet destined for a remote network arrives at the router, the router matches the destination network to a route in the routing table. If a match is found, the router forwards the packet to the IP address of the next hop router using the interface identified by the route entry.
A next hop router is the gateway to remote networks.
For example, in the figure, a packet arriving at R1 destined for either the 10.1.1.0 or 10.1.2.0 network is forwarded to the next-hop address 184.108.40.206 using the Serial 0/0/0 interface.
Networks directly connected to a router have no next-hop address, because a router can forward packets directly to hosts on these networks using the designated interface.
Packets cannot be forwarded by the router without a route for the destination network in the routing table. If a route representing the destination network is not in the routing table, the packet is dropped (that is, not forwarded).
However, just as a host can use a default gateway to forward a packet to an unknown destination, a router can also be configured to use a default static route to create a Gateway of Last Resort. The Gateway of Last Resort will be covered in more detail in the CCNA Routing course.