Probing Remote Hosts With the ping Command

You can use the ping command to determine the status of a remote host. When you run ping, the ICMP protocol sends a datagram to the host that you specify, asking for a response. ICMP is the protocol responsible for error handling on a TCP/IP network. When you use ping, you can find out whether an IP connection exists for the specified remote host.

The following is the basic syntax of ping:

/usr/sbin/ping host [timeout]

In this syntax, host is the name of the remote host. The optional timeout argument indicates the time in seconds for the ping command to continue trying to reach the remote host. The default is 20 seconds. For additional syntax and options, refer to the ping(1M) man page.

How to Determine if a Remote Host Is Running

• Type the following form of the ping command:

  $ ping hostname

  If host hostname is accepting ICMP transmissions, this message is displayed:

  hostname is alive

  This message indicates that hostname responded to the ICMP request. However, if hostname is down or cannot receive the ICMP packets, you receive the following response from the ping command:

  no answer from hostname

How to Determine if a Host Is Dropping Packets

Use the -s option of the ping command to determine if a remote host is running but nevertheless losing packets.

• Type the following form of the ping command:

  $ ping -s hostname

Example 8-13 ping Output for Detecting Packet Dropping

The ping -s hostname command continually sends packets to the specified host until you send an interrupt character or a time out occurs. The responses on your screen resemble the following:

& ping -s host1.domain8
PING host1.domain8 : 56 data bytes
64 bytes from host1.domain8.COM (172.16.83.64): icmp_seq=0. time=1.67 ms
64 bytes from host1.domain8.COM (172.16.83.64): icmp_seq=1. time=1.02 ms
64 bytes from host1.domain8.COM (172.16.83.64): icmp_seq=2. time=0.986 ms
64 bytes from host1.domain8.COM (172.16.83.64): icmp_seq=3. time=0.921 ms
64 bytes from host1.domain8.COM (172.16.83.64): icmp_seq=4. time=1.16 ms
64 bytes from host1.domain8.COM (172.16.83.64): icmp_seq=5. time=1.00 ms
64 bytes from host1.domain8.COM (172.16.83.64): icmp_seq=5. time=1.980 ms

^C

----host1.domain8  PING Statistics----
7 packets transmitted, 7 packets received, 0% packet loss
round-trip (ms)  min/avg/max/stddev = 0.921/1.11/1.67/0.26

The packet-loss statistic indicates whether the host has dropped packets. If ping fails, check the status of the network that is reported by the ifconfig and netstat commands. Refer to Monitoring the Interface Configuration With the ifconfig Command and Monitoring Network Status With the netstat Command.