| We have managed to communicate between two machines connected on our network, but how did helium know where to send and receive information about hydrogen? The answer lies in a mechanism named "routing." The kernel maintains a structure known as a "routing table." This contains information about where packets need to be sent, or routed, to get to their destination. We can view the routing table with netstat: hydrogen# netstat -rn Routing Table: Destination Gateway Flags Ref Use Interface ----------------- ---------------- ----- ----- ------ --------- 192.168.22.0 192.168.22.1 U 3 5 hme0 127.0.0.1 127.0.0.1 UH 0 2 lo0 hydrogen# This shows us that any packets destined for the 192.168.22.0 network will be routed through a gateway with an IP address of 192.168.22.1 (i.e., the network interface that we defined earlier). It also shows that the loopback interface is routed, again through itself. This is a fairly simple implementation of a routing table, but we will see how it can be expanded later. |