Mac OS X Leopard - ARCAism

theory behind Ping is that any machine that receives a ping is supposed to echo it back. Unfortunately,
Ping has been abused by malware in the past—hence stealth mode.
To use Ping in Network Utility, enter an IP address or domain name. Ping will then list the
pings as they return, along with how long it took them to traverse the network. This is useful in
any number of ways.
For example, if your web site goes down but your web host responds to pings, you can
deduce that the host program crashed, but that the server is OK. If the server does not respond
to pings, you can assume something is wrong on a hardware level.
Similarly, if your server responds by IP address, but doesn’t respond by domain name, you
can deduce that something is wrong with the domain name system (DNS). Further investigation
would be needed to determine if the domain name has expired, or if there is something else going
on. These can be determined elsewhere in Network Utility.
Lookup
The Lookup tab combines the nslookup and dig tools to query DNS, which converts humanreadable
web addresses to the numerical IP addresses used by computers. The information
returned by Lookup varies by host, but at the very least you can use it to get the IP address of a
given server name.
Traceroute
Traceroute maps the path of packets as they travel to a given server address. Aside from being
kind of interesting, it’s a useful diagnostic tool. When a server is unreachable, there’s no way of
knowing where the packets are being stopped. By using Traceroute, you can figure out who you
need to call to get traffic flowing.
Like Ping, Traceroute has been abused by nefarious forces, so some servers will block
Traceroute requests. Even so, you can usually get to the outer bounds of a given network, which
will certainly tell you something, so Traceroute remains a good thing to have in your toolbox.
Whois
CHAPTER 20 LEOPARD NETWORKING 357
As opposed to the tools in Lookup, which convert domain names into IP addresses, Whois
queries domain registries to determine who owns them. There are a couple of reasons why you
might want to know this.
If your site is down and your server is reachable by IP address, but not by domain name, one
possibility is that your domain name has expired or has been stolen. Checking the Whois information
will let you know for sure. If Whois checks out OK, you can begin suspecting something
is wrong with the name server itself.
Should you find your packets are being stopped at a certain node via Traceroute, Whois will
tell you who you need to call about it. It’s also a good way to see if a domain name is available,
and if it’s not, to see when it expires. There’s no sense putting up good money for a domainwatching
service if the registration is not going to expire for another five years.
As with many parts of the Internet, Whois registries have been abused. Putting your name,
e-mail address, home address, and telephone number where anyone can get them is a potential
privacy concern.
As such, some registrars now offer anonymous registration, whereby they will register the
domain in their own name on your behalf, preventing people from getting any useful information
about you. As with any such tactic, this certainly improves security by some degree, while
breaking the Internet by another.