On Thu, 5 Feb 2004, Michael Havens wrote:
> Why could I ping things with out the www but not with the www?
Different IP addresses.
Some systems allow pings to work. And some don't.
> added the www and it wouldn't ping. I then pulled up the page with the
> www and there it was. So then what.... was there a redirection from the
> one w/o the www to the one with?
A webpage is using TCP (port 80). The ping is using ICMP. The protocols
are different. Many admins setup firewalls for ICMP echos (request and/or
response).
What is the unix trace route command?
An IP packet has a time-to--live counter. It decreases by one each time it
is routed. So when an IP packet goes from router to router, it decreases.
traceroute sets it to one.
Then attempts to do three UDP port 33434 probes of the destination. But
since the TTL is at one, the router doesn't route it and just responds
saying that the time has exceeded. Then traceroute prints the name of the
host, the TTL used and how much time it took for each probe.
Then traceroute tries with the TTL set to two. And so on (repeat previous
paragraph).
Jeremy C. Reed
http://www.reedmedia.net/
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