Setting up subnets and routing

Verifying correct routing behavior

The netstat -r command provides information about the usage of each route configured on your system. A route consists of a destination host or network and a network interface used to exchange packets. Direct routes are created for each interface attached to the local host.

At a minimum, your routing table should display entries for the loopback mechanism (localhost), the local network, the local hostname, and the IP Multicasting route, 224. The following is a typical display:

   Routing tables
   Destination     Gateway         Flags     Refs     Use   Interface
   localhost       localhost       UH        24       66    lo0
   172.16.118      nile            UC        1        0     net0
   nile            localhost       UGHS      3        36    lo0
   224             nile            UCS       0        0     net0
   ...

The columns display:

Destination

Network or host to which this route allows you to connect.

Gateway

Name of the gateway you configured for this route. If you are directly connected, this is a local address. Otherwise, it is the name of the host through which packets must be routed.

Flags

State of the route. For a complete list, refer to route(1Mtcp). Common states are:

C: new routes are cloned from this route (used for multicast routing)
G: a route to a gateway
H: a route to a host
N: a route to a network
S: a static route
U: the route is up

Refs

Current number of active connections using the route. Connection-oriented protocols normally hold on to a single route for the duration of the connection, while connectionless protocols obtain a route, then discard it as needed.

Use

Current number of packets sent using this route.

Interface

Name of the physical network interface used to begin the route.

If one or more of these routes are missing, you may see routing errors when you try to contact other hosts. You can add routes manually using the route add command. See route(1Mtcp) for more information.