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RE: icmp: echo reply? Am I being attacked?

	From the looks of things, your computer (neural1.fe.up.pt) is being
	pinged by the remote computer (bozzman.comesurfthe.net).  The output
	you quoted in your e-mail is your computer's response to the ping.

	A 'ping' consists of two types of ICMP packets; an "echo-request",
	and an "echo-reply".

	Take a look at the network traffic for "echo-requests" from the
	that your machine is sending the "echo-reply" to; you should see

	i may be incorrect with this next statement (corrections anyone?),
	you do not see any "echo-requests" that correspond to the
	you are seeing, then it may be possible that someone has compromised
	your machines.  This is probably not the case, though i can't say
	certain.  The bottom line is that if you see the "echo-requests",
	mystery solved.  Otherwise, you may wish to post again with more

	Hope this helps.  Can anyone else provide more info?

John Vivian
Network Security Analyst

-----Original Message-----
From: Nuno Faria [mailto:nfaria@fe.up.pt]
Sent: Wednesday, July 26, 2000 2:42 PM
To: debian-security@lists.debian.org
Subject: icmp: echo reply? Am I being attacked?

Dear list members,

First of all let me state where I stand.

I've been using Linux (Debian) for one year now. During this year I've
learnt quite a lot but on the issue of network and security I'm a
complete newby.

Now I think I have a security problem (although it is not exclusively
mine). The problem is as follows:

I am the administrator of three PCs in a local network. They all have
real IP adresses.

Sometimes, withou any aparent reason, some of the computers in this
network start producing network trafic without any aparent reason. I do
netstat and there is no indication of a network conection. I do "tcpdump
host machinename" and I get a series of:

17:32:27.620336 neural1.fe.up.pt > bozzman.comesurfthe.net: icmp: echo

not necessarily with the same machine adress (bozzman.comesurfthe.net).
The increase in the network trafic can be as high as 50kB/s.

This is not a Debian or Linux specific problem as it also hapens on
another machin running Digital Unix, but on the other hand, if I change
one of the PCs from Linux to Win NT4 the problem stops. It reapears when
I change it back to Linux.

Can you help me? Can you point me to some document I might read to find
information related to this subject?

Thanks in advance,

Nuno Faria

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