Ping Command in Linux: Test Network Connectivity and Latency

The ping and ping6 command in Linux uses the ICMP protocol to send ECHO REQUEST messages and receive ECHO RESPONSE to test the connection between the system and another machine on the network.

It returns the response time that a network packet takes to go and return. Very useful for diagnosing a connection. The ping will test indefinitely until Ctrl-c is pressed.

Ping also has a version for IPv6, called ping6. Its operation is similar to the IPv4 ping.

The most frequent options are:

• -c num: This option makes the ping test the connection a specific number of times.
• -q: This option makes ping only show the final connection test statistics.

Example:

$ ping 192.168.1.1PING 192.168.1.1 (192.168.1.1) 56(84) bytes of data.64 bytes from 192.168.1.1: icmp_seq=1 ttl=64 time=0.175 ms64 bytes from 192.168.1.1: icmp_seq=2 ttl=64 time=0.120 ms64 bytes from 192.168.1.1: icmp_seq=3 ttl=64 time=0.115 ms— 192.168.1.1 ping statistics —5 packets transmitted, 5 received, 0% packet loss, time 4000msrtt min/avg/max/mdev = 0.115/0.128/0.175/0.026 ms

Ping is widely used to test if a machine is connected to the local network or if it is reachable on the remote network. For ping to work correctly, the network in question must not have any ICMP filter, especially the ECHO REQUEST and ECHO RESPONSE types.

The ping command can indicate the following possible network problems:

Name Resolution Problem:

If when executing ping on a given host using a network name (host.certificacaolinux.com.br) the ping takes a long time to respond, and cannot resolve the name to IP, it means:

• The DNS server may be wrong (check the /etc/resolv.conf file);
• The DNS server cannot be accessed (ping using the DNS server IP);
• There is a UDP port 53 filter between the computer and the DNS server (check the iptables);

Connectivity Problem:

If when executing ping, a given host does not respond, it may mean:

• The destination host is down;
• There is no route between the computer network and the destination host (check the routing table);
• The default gateway is wrong (check the routing table);
• The Network Address Translation has a forwarding or address translation problem (check the firewall);
• There is an ICMP ECHO and ECHO-REPLY filter on the network;

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