Mick:
On Monday 11 December 2006 20:56, Sergio Polini wrote:
Yes, it was OT and very few of you are interested ;-)
However, somebody would like to know who the killer was.
The original subject was wlan0 is ssslw [99% SOLVED]
because pinging the Belkin F5D7230-4 wireless router worked from
Windows but not from Linux.
The answer is: because Windows sends ICMP messages with 32 bytes
of data, Linux sends them with 56 bytes of data.
Moreover, Linux IP datagrams have the DF (don't fragment) bit
set, Windows ones have not.
On Linux, ping -s 15 192.168.2.2 works.
How did you ever find this out?!
I used two tools: Douglas Comer, Internetworking with TCP/IP, and
Wireshark (former ethereal).
I'm still installing my new laptop, f.i., I've not yet setup a
firewall. My former firewall was based on the Iptables Tutorial by
Oskar Andreasson, but I didn't understand all the details. So I've
started studying, i.e. reading Comer and looking at frames,
datagrams, etc. by Wireshark.
I needed that. For example, I had used nmap to look for an echo port
on the Belkin router, but ping, i.e. ICMP, doesn't know anything
about ports!
As to the ping problem, I started a Windows virtual machine by VMware
Player, then Wireshark both in the Linux real machine and in the
virtual one, then pinged the Belkin router. Looking at the output
produced by the Linux Wireshark and by the virtual Windows one, there
were just two differences: the DF bit, and the data field length in
the ICMP messages.
I'll know that's another thing to test when an access point
is playing up. I wonder why belkin is set up this way.
I think that a router should send ICMP messages such as fragmentation
needed and DF set (Type 3, , Code 4) and time to live exceeded in
transit (Type 11, , Code 0), but Belkin does not (traceroute, and
tracert, 192.168.2.1 print stars).
The Belkin 54G wireless router, F5D7130, had serious security holes:
http://www.governmentsecurity.org/archive/t15618.html
My model, F5D7230, is more secure. Eventually too much ;-)
Thanks for sharing. :-)
Alan McKinnon:
I'm very glad you did post this update as here in the office we had
this very problem three weeks ago. One morning every non-Windows
host in our building suddenly could not see past the gateway, could
not ping it and was essentially off-air. We eventually tracked it
down to one of these Belkin wireless routers, but never figured out
why it was doing what it did.
Now we do know, so thanks for the heads-up!
I must thank all of you. Gentoo would not be such an attractive system
without the continuous support by all of you.
Sergio
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