ifconfig Command

The ifconfig command displays information about the configuration of an interface that you specify. Refer to the ifconfig(1M) man page for details. The syntax of ifconfig follows:

ifconfig interface-name [protocol_family]

ifconfig Command Task Map

Table 4-7 ifconfig Command Task Map

How to Get Information About a Specific Interface

1. Become superuser.

2. On the command line, type the following command.

   # ifconfig interface

For an le0 interface, your output resembles the following:

le0: flags=863<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
 	inet 129.144.44.140 netmask ffffff00 broadcast 129.144.44.255
ether 8:0:20:8:el:fd

The previous flags section shows that the interface is configured "up," capable of broadcasting, and not using "trailer" link-level encapsulation. The mtu field tells you that this interface has a maximum transfer size of 1500 octets. Information on the second line includes the IP address of the host you are using, the netmask being currently used, and the IP broadcast address of the interface. The third line gives the machine address (Ethernet, in this instance) of the host.

How to Get Information About All Interfaces on a Network

A useful ifconfig option is -a, which provides information on all interfaces on your network.

1. Become superuser.

2. On the command line, type the following command.

   # ifconfig -a interface

This command produces, for example:

le0:  flags=49<UP,LOOPBACK,RUNNING> mtu 8232
     inet 127.144.44.140 netmask ff000000 
le0:flags=863<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
     inet 129.144.44.140 netmask ffffff00 broadcast 129.144.44.255
ether 8:0:20:8:el:fd

Output that indicates an interface is not running might mean a problem with that interface. In this instance, see the ifconfig(1M) man page.

netstat Command

The netstat command generates displays that show network status and protocol statistics. You can display the status of TCP and UDP endpoints in table format, routing table information, and interface information.

netstat displays various types of network data, depending on the command-line option that is selected. These displays are the most useful for system administration. The syntax for this form follows:

netstat [-m] [-n] [-s] [-i | -r] [-f address_family]

The most frequently used options for determining network status are s, r, and i. See the netstat(1M) man page for a description of the options.

netstat Command Task Map

Table 4-8 netstat Command Task Map

How to Display Statistics by Protocol

The netstat -s option displays by protocol statistics for the UDP, TCP, ICMP, and IP protocols.

• On the command line, type the following command.

  % netstat -s

The result resembles the display that is shown in the following example. (Parts of the output have been truncated.) The information can indicate areas where a protocol is having problems. For example, statistical information from ICMP can indicate where this protocol has found errors.

UDP
 
      udpInDatagrams      =  39228     udpOutDatagrams     =  2455  
      udpInErrors         =     0
 
TCP
 
      tcpRtoAlgorithm     =     4      tcpMaxConn          =    -1
      tcpRtoMax           = 60000      tcpPassiveOpens     =     2
      tcpActiveOpens      =     4      tcpEstabResets      =     1
      tcpAttemptFails     =     3      tcpOutSegs          =   315
			.
			.
IP
 
      ipForwarding        =     2      ipDefaultTTL        =   255
      ipInReceives        =  4518      ipInHdrErrors       =     0
			.
			. 
ICMP
 
      icmpInMsgs          =     0      icmpInErrors        =     0
      icmpInCksumErrs     =     0      icmpInUnknowns      =     0
			.
			. 
 
IGMP:
 
0 messages received
0 messages received with too few bytes
0 messages received with bad checksum
0 membership queries received
0 membership queries received with invalid field(s)
0 membership reports received
0 membership reports received with invalid field(s)
0 membership reports received for groups to which we belong
0 membership reports sent

How to Display Network Interface Status

The i option of netstat shows the state of the network interfaces that are configured with the machine where you ran the command.

• On the command line, type the following command:

  % netstat -i

netstat -i produced the following sample display:

 
Name Mtu  Net/Dest     Address   Ipkts    Ierrs Opkts    Oerrs  Collis  Queue
le0  1500 b5-spd-2f-cm tatra     14093893 8492  10174659 1119   2314178   0
lo0  8232 loopback     localhost 92997622 5442  12451748 0      775125    0

Using this display, you can determine the number of packets a machine transmits and receives on each network. For example, the input packet count (Ipkts) that are displayed for a server can increase each time a client tries to boot, while the output packet count (Opkts) remains steady. This outcome suggests that the server is seeing the boot request packets from the client, but does not realize that the server is supposed to respond to them. This confusion might be caused by an incorrect address in the hosts, ipnodes, or ethers database.

However, if the input packet count is steady over time, then the machine does not see the packets at all. This outcome suggests a different type of failure, possibly a hardware problem.