Re: Linux PC cannot ping, but Windows can?

From: Moe Trin (ibuprofin_at_painkiller.example.tld)
Date: 01/21/05


Date: Thu, 20 Jan 2005 18:02:17 -0600

In article <csog3n$3og$1@news3.bu.edu>, nick wrote:

>>>> While I agree it seems to be something wrong with the home router/fw
>>
>> I also agree
>
>But my home Linux can ping/ssh/http all other hosts I tried successfully.
>And my home Windows PC can access my office Win XP PC without any problem
>while my home Linux has the problem. Sounds my office firewall problem.
>Since both my home WinXP and Linux PC use NAT and the IP packages from my
>home should be wrapped by my home firewall/gateway(Belkin) with the same
>header (source IP address, etc) assigned to my home Belkin.

The only way to prove that would be to look at the packets from your
windoze and Linux boxes and compare them, then look at the packets
coming out of the Belkin that go to the Internet. It might be ECN,
but that's about the only thing I can think of.

echo 0 > /proc/sys/net/ipv4/tcp_ecn

on the Linux box would turn that off.

>Looks my office firewall exam the payload of the IP packages from my home
>router and block the ones originated from the Linux PC.

Highly unlikely, as for a ping, the only difference would be the TTL. You
could try using windoze TRACERT and seeing what a connection trace looks
like, then trying the same thing with Linux traceroute. One problem is
that the Linux version defaults to using UDP (windoze is using ICMP echos)
and you need to use the '-I' option on most versions to cause the Linux
version to use ICMP (SuSE broke this if you are trying to use their version).

On Fri, 14 Jan 2005, "John Mason Jr <notvalid@cox.net.invalid>" suggested
using 'tcptraceroute' from Linux. That's not a normal part of a distribution,
and he gave you the URL of where to find it. Try that as well.

For than matter, you could try using 'nmap' to see what your systems at
work are doing, but I'd recommend warning the network administrator there
BEFORE you try, as he might think the place is under attack, and call out
the National Guard or something.

       Old guy



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