All,
To partly reply to my own question - one of my flaws was keeping $HOME_NET as
10.0.0.0/8 - this prevented most of my test traffic from triggering since my
tests were coming from $HOME_NET and not $EXTERNAL_NET. This was significant
where the rule I was testing was of the form $EXTERNAL_NET -> $HOME_NET
I'm still getting the ICMP messages as well, so I have to presume that those
packets are actually out there also, but I don't understand why they are being
generated since as observeved from the fact that I can SSH and ping the host it
is not actually unreachable.
David
From: David Ryan
Sent: 30 May 2007 11:10
To: 'snort-users@lists.sourceforge.net'
Subject: Everything being triggered as 1:486:4 ICMP unreachable
Hi all,
I built and tested a number of machines and shipped them out to remote sites
recently. Now that they are at the remote site I am trying to tweak them a bit
but I have run into some pretty basic problems that I hadn't come across
before. I'm sure the devices were logging events properly before I shipped
them, but now every time I try to test a rule I get back the following line -
May 30 10:35:14 <hostname> snort[5017]: [1:486:4] ICMP Destination Unreachable
Communication with Destination Host is Administratively Prohibited
[Classification: Misc activity] [Priority: 3]: {ICMP} <probe address> -> <my
test machine address>
There are a couple of relevant points here -
$HOME_NET is defined as 10.0.0.0/8 and $EXTERNAL_NET is defined as !$HOME_NET
The probe has an ip address assigned in a /24 10.x.x subnet
My test machine has an ip address assigned in a different /23 10.x.x subnet
I know there is no routing problem since I am SSH'd in to the probe from my
test machine and I can ping in both directions
I am trying to read through the rule generating this message to see what is
being triggered, but it looks pretty much like it is triggered on what it
describes - an ICMP destination unreachable notification packet.
I looked back through the old logs and see the following from before I shipped
it off so I know it was logging correctly -
May 15 12:08:10 <hostname> snort[2331]: [1:2189:3] BAD-TRAFFIC IP Proto 103 PIM
[Classification: Detection of a non-standard protocol or event] [Priority: 2]:
{PIM} <old probe address> -> 224.0.0.13
The only thing that changed is the probe IP address, but both the old and new
configs used DHCP and I'm pretty sure that when I was testing before the IP
address changed and it still continued to log OK.
Any ideas what is causing this trigger ? As above, I am reasonably sure that
it is not an actual ICMP destination unreachable packet because the destination
is reachable . . .
David
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