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[Snort-users] Everything being triggered as 1:486:4 ICMP unreachable

Subject: [Snort-users] Everything being triggered as 1:486:4 ICMP unreachable
Date: Wed, 30 May 2007 06:10:10 -0400
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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