[Snort-users] Passing IP Addresses best practices

Erek Adams erek at ...950...
Tue Sep 23 10:40:07 EDT 2003

On Tue, 23 Sep 2003, Mike Burkhouse wrote:

> I saw that in the FAQ, but the examples used private IPs.  Being fairly new
> at this, I didn't know if implied that it was a really_bad_idea to pass
> public IPs, which is why I am asking about best practices.
> I will definitely look into BPF more closely.  Thank you for your advice.

There is a very subtle difference between the two.  You need to make sure
that you make the right choice for you setup.


	*  Pass rules.  Can be setup to ignore a host or set of hosts.
You can even ignore on content.  In your case an idea might be:

	var BLACKBERRY_BOXES [123.456.789.010,123.456.789.011]
	pass tcp $BLACKBERRY_BOXES any -> $MAIL_SERVERS 110 <stuff>

	You can adjust the BLACKBERRY_BOXES var as you need or use a CIDR
subnet mask such as  You can also change <stuff> to
something specific, or you can just end the rule there.  IOW, you can
ignore all incoming tcp port 110 traffic from the BBservers to your
mailservers, or ignore on something specific by using a 'content: <bleh>'

	* BPF filter.  Drops the data before it even _gets_ to Snort.
Very useful if you have a lot of traffic that you want to ignore, since
there is not a CPU overhead from using the BPF.

	snort <options> 'not src host and dst port 110 and
dst host <foo>'

Hope that helps!

Erek Adams

   "When things get weird, the weird turn pro."   H.S. Thompson

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