[Snort-users] Order of rules

Joel Esler (jesler) jesler at ...589...
Fri May 2 10:36:28 EDT 2014


Rule processing does not end after the first hit.

The first hit could be an alert and a pass would take precedence w/ no
command line/snort.conf options to change that.

Rule order in the config file does not matter, rule evaluation is not linear.

They will be processed in the order in which the fast-pattern matches are
found in the payload.  The first pattern to occur, rules w/ that pattern
will be evaluated first and so on.  And the rules within that matching end
state are evaluated in a tree of options.  How options are added into the
tree is not deterministic from one run to another.

J

On May 1, 2014, at 3:31 PM, Dave Corsello <snort-users at ...15598...<mailto:snort-users at ...15598...>> wrote:

I looked pretty hard for this information and couldn't find it, so maybe
this will be useful to someone:  it looks like rules with the same
priority and similar action are processed in sid order.

On 4/29/2014 5:35 PM, Dave Corsello wrote:
Let me narrow that down.  Assume that no command line options or
snort.conf options are used to change the order in which rule actions
are taken, and that rule processing ends after the first hit.
Basically, I want to know if changing the physical order of two drop
rules with the same priority in my local.rules file makes a difference,
or if there's some other default sort order that takes precedence.


On 4/29/2014 9:07 AM, Dave Corsello wrote:
Here's a very basic question:  In what order are snort rules processed:
the order in which they are listed in a rules file, or in gid/sid order?

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