This might be a stupid question so please forgive me.

I have broadband via ADSL at home (through BT Openworld). I have my
computer attached to a modem/router which is plugged into the ADSL

For some reason, although my connection normally works perfectly, I
cannot reach the occasional address. For example, I cannot reach
f4.grp.yahoofs.com (yahoo groups) although I can reach
f3.grp.yahoofs.com. At first I thought their server must be down but
now I know that other people can reach it just fine!

I have tried to ping and traceroute the ip address ( and
it loses 100% of packets, or in traceroute just shows line after line
of * * *.

I am very curious to learn and would like to know how to follow this
up. Can anyone help me?

I have set up the DNS Servers in my network settings as instructed by
my ISP and like I said above, normally I have no problems resolving
addresses. But every now and then a particular address is unreachable.
The yahoo groups one is particularly strange because in Britain my ISP
is partnered with Yahoo.

Any advice is greatly appreciated.