[Offer] Cisco IOS Commands – Using Extended Ping For Network Troubleshooting

[4cisco]

Please Login to view content

The extended ping command is a very important part of any network engineer’s Cisco IOS commands knowledge. Many beginners do not know how to use this command effectively, but it is definitely a must-know and can isolate many network issues. In this post, I’ll go through some of the most important and useful parameters of this command:
Target IP address

The target IP address is the IP you want to send the ping/ICMP packet to. This is fairly straightforward, but one important note that if this IP is not routable from this router, you won’t be able to reach it, and will get no replies. The next step would be to do a traceroute to further isolate the issue.
Repeat count

Some physical line problems might only show up upon repeated ping tests. If it’s an intermittent issue, it’s best to put a larger number to simulate a stress test in order to ensure that there are no issues. For example, 1,000 or 10,000 packets might be a suitable number.
Datagram size


For stress test purposes, you can put a larger number in the datagram size to test for larger packets. It is not recommended to put a datagram size larger than the maximum MTU size of all the routers along the routing path as this would mean the packets would be fragmented (unless you are testing whether fragmentation is working properly). For an TCP/IP network running on ethernet, a good datagram size to use is 1500.
Some issues might also only show up with larger datagram sizes. These are usually related to some fragmentation issue along the way. It makes sense to test with larger datagram sizes as well as small ones in order to be sure.
Source address or interface

This part of the extended ping command is very useful to test whether it’s a routing issue or a switching issue. If you reach the directly connected router for a problematic host, and pings are successful when sourced from a directly connected interface (but not from another interface which is not directly connected), it usually indicates a routing configuration or process issue on that router, since no routing is needed for directly connected interfaces.