* Querying IP addresses with ping
Last time, we pointed out that the usefulness of the ping and tracert commands has been severely limited by the fact that in order to protect from denial-of-service attacks, many systems now do not respond to pings. Nevertheless, there is still at least one useful function provided by ping – the identification of the IP address of a given network resource.
As we’ve noted on several occasions, the users’ perception that “the network is down” can be due to a wide variety of root causes, many of which do not have anything to do with end-to-end transmission. For instance, if a Web site cannot be reached, the users complain that “the network is down.” However, it’s quite possible that the problem with reaching the site is due to the DNS being unavailable rather than the transport network having a problem.
When you do a “ping,” the first step is querying the DNS – and the IP address reported – for that particular domain. For instance, if one pings www.webtorials.com, which happens to be a real domain, the ping command returns a message that it is pinging www.webtorials.com [209.133.56.251] with 32 bytes of data. The ping “fails,” but now you have a real IP address that you may try.
This address may be inserted into a browser, so that instead of entering http://www.webtorials.com you enter http://[the IP address]. (In some cases, if the domain is subhosted, this may or may not work, so it’s a good idea to try the target in advance to make sure that your test is valid.)
It’s a simple but great tool for testing which part of the network is failing. In fact, we highly recommend that users store some favorite IP addresses, including, if possible, the address of the first local router as a way to determine whether a connectivity problem is in the workstation or somewhere farther out in the network.
By the way, if you’re wondering why we wrote the above URL as http://[the IP address] instead of substituting the string of numbers, we’ll cover that related issue in an upcoming newsletter.
