 |
|
Of fundamental importance to this discussion is the fact that
the destination IP address is a Class A, B, or C unicast address. In Figure 5-1, we have a
simple network with a source (172.16.1.1) that is sending to a
destination (172.16.5.1). It is a simple matter for each router to
determine the path to the destination. Assume that only default and
directly connected routes are being used in routers A, B, and C.
When the packet from the source arrives at router A, the destination
address in the IP packet is examined and checked against the routing
table. Router A has four routes, three are directly attached, and
one is a default route that says “send every packet that is not
destined for one of my three directly attached networks out the
serial link.” Routers B and C have similar routing tables. As the
packet travels through the network, each router checks the
destination IP address, consults the routing table, and forwards the
packet out the proper interface. |
| |