Network Diagnostics: Ping

Ping is one of the most useful tools in network troubleshooting.

Testing reachability using the ping command (ping 192.168.1.254) can quickly offer insight into any network issues

On a Cisco router, a successful ping response will be marked with a !; a ping time out will be marked with a .

The success rate is measured as a percentage of pings that were succesful.

A round trip time is also displayed in the format of minimum ping time / average ping time / maximum ping time

Additional Parameters

Ping has some additional parameters that can be set to aid in troubleshooting.

The repeat parameter can change the number of pings from the default 5 to any lower or higher value.

The size parameter can adjust the size of the ping packet sent to the destination.

The source-interface allows the source address packets of the pings being sent to be modified. This can be used for ensuring that routing to a particular subnet works.

Ping also has an extended ping mode, that can be enabled by just typing ping and pressing enter

Extended ping prompts for various options to be chosen before sending the ping packets:

Protocol – IP, Novell, AppleTalk, CLNS. Default is IP

Target IP Address – The destination address to send the pings

Repeat Count – Number of ping packets to send, default is 5

Datagram Size – The size of the ping packets, default is 100 bytes

Timeout in seconds – How long until considering a ping has timed out

Extended Commands – Provide even more options if ‘Yes’ is chosen

Source Address or Interface – Where to source the ping packets

Type of Service (ToS) – Type of service to be used for each ping, default is 0.

Set DF bit in IP Header – Set Do Not Fragment in IP header, default is No.

Data Pattern – The data pattern used in ping packets, the default is 0xABCD

Loose, String, Record, Verbose:

• Loose – Specifies the hops that ping packets should traverse
• Strict – Same as loose but packets can only traverse selected hops
• Record – Displays the IP addresses of first nine hops
• Timestamp – Displays round trip time to destination for each ping
• Verbose – Default option that is automatically selected with any and all options

Real World Examples

Setting the MTU to a higher value and setting the Do Not Fragment bit can be a great way of testing the maximum MTU size across one or several links.

Changing the Type of Service can test the Quality of Service parameters that are configured on links; though some routers do not respect the Type of Service field set in ICMP packet.s

Setting a custom data pattern can be a good method of validating coding or link errors across a link.