[Snort-users] Vlan Tagging Issue with Snort

Russ Combs rcombs at ...1935...
Mon Sep 13 18:44:44 EDT 2010


Not sure what is causing the issue you report but see below for another
comment.

On Mon, Sep 13, 2010 at 5:04 PM, infosec posts <infosec.posts at ...11827...>wrote:

> Unfortunately, I discovered that this configuration is breaking all of
> my signatures that use "flow:to_client,established", so I assume it's
> messing with stream5 and all of my other rules which use checks that
> take advantage of stream5.  I'm not sure why this is, as snort should
> be seeing the entire (both sides of) tcp conversation setup and
> teardown now (as confirmed by using the same filter on tcpdump).
>
> For a given signature, changing "flow:to_client,established" produces
> the following results:
>
> flow:stateless; - signature alerts
> flow:statless,no_stream; - signature alerts
> flow:stateless,only_stream; - no alert
>
> Obviously, I don't want to re-write my rules to exclude flow checks &
> such, even via an automated process.  If anyone has insight into what
> is happening or additional troubleshooting/information gathering
> procedures, I'd appreciate the help.  Thanks!
>
> Here's my stream5 config (unchanged since before the network gear
> changed and we started getting the 802.1q traffic) :
> preprocessor stream5_global: max_tcp 8192, track_tcp yes, track_udp no
> preprocessor stream5_tcp: policy first, use_static_footprint_sizes
>
> snort[4576]: Stream5 global config:
> snort[4576]:     Track TCP sessions: ACTIVE
> snort[4576]:     Max TCP sessions: 8192
> snort[4576]:     Memcap (for reassembly packet storage): 8388608
> snort[4576]:     Track UDP sessions: INACTIVE
> snort[4576]:     Track ICMP sessions: INACTIVE
> snort[4576]:     Log info if session memory consumption exceeds 1048576
> snort[4576]: Stream5 TCP Policy config:
> snort[4576]:     Reassembly Policy: FIRST
> snort[4576]:     Timeout: 30 seconds
> snort[4576]:     Maximum number of bytes to queue per session: 1048576
> snort[4576]:     Maximum number of segs to queue per session: 2621
> snort[4576]:     Options:
> snort[4576]:         Static Flushpoint Sizes: YES
>

This should be NO for live traffic, so remove use_static_footprint_sizes.

The manual will be updated to make that more clear.  It was intended for
testing only.

 snort[4576]:     Reassembly Ports:
> snort[4576]:       21 client (Footprint)
> snort[4576]:       23 client (Footprint)
> snort[4576]:       25 client (Footprint)
> snort[4576]:       42 client (Footprint)
> snort[4576]:       53 client (Footprint)
> snort[4576]:       80 client (Footprint)
> snort[4576]:       110 client (Footprint)
> snort[4576]:       111 client (Footprint)
> snort[4576]:       135 client (Footprint)
> snort[4576]:       136 client (Footprint)
> snort[4576]:       137 client (Footprint)
> snort[4576]:       139 client (Footprint)
> snort[4576]:       143 client (Footprint)
> snort[4576]:       445 client (Footprint)
> snort[4576]:       513 client (Footprint)
> snort[4576]:       514 client (Footprint)
> snort[4576]:       1433 client (Footprint)
> snort[4576]:       1521 client (Footprint)
> snort[4576]:       2401 client (Footprint)
> snort[4576]:       3306 client (Footprint)
>
>
>
> On Fri, Sep 10, 2010 at 10:20 AM, infosec posts <infosec.posts at ...11827...>
> wrote:
> > Looks like those filters are going to work, Bamm; thanks!  I thought
> > there had to be a solution like that, but I hadn't found the right
> > groupings yet.  You are also correct that the second filter should be
> > "port 80 or port 443"; that was an error when I typed this email, as I
> > wasn't looking at my actual filters when I typed it up.
> >
> > I also had an individual reply that suggested setting up a virtual
> > interface on my monitor nic and setting it as a vlan tagged port.  I
> > haven't tested that yet, but wanted to mention it in case it helps
> > someone else reading the list at some point.
> >
> > On Fri, Sep 10, 2010 at 9:52 AM, Bamm Visscher <bamm.visscher at ...11827...>
> wrote:
> >> Use an "OR" to grab vlan or ip traffic, like so:
> >>
> >> BPF="(ip and not port 80 and not port 443) or (vlan and not port 80
> >> and not port 443)"
> >> BPF="(ip and port 80 and port 443) or (vlan and port 80 and port 443)"
> >>
> >> Although the "port 80 *and* port 443" doesn't make any sense to me
> >> (port 80 *or* port 443 maybe)?, but it's your filter.
> >>
> >> Bamm
> >>
> >>
> >> On Thu, Sep 9, 2010 at 7:05 PM, infosec posts <infosec.posts at ...11827...>
> wrote:
> >>> Greetings Snort Gurus,
> >>>
> >>> Our network folks were recently forced to make some architectural and
> >>> equipment changes that are creating an issue with our snort
> >>> monitoring.  The core of the problem is that on the switch that sends
> >>> our IDS sensor traffic via a monitor port, outbound traffic is not
> >>> tagged, but inbound traffic (from the Internet) come across at trunk
> >>> and have 802.1Q vlan tags.  This cannot be changed due to
> >>> architectural restrictions and (sad/ridiculous/stupid) limitations in
> >>> the network swtiches.  I know that snort supports and understands vlan
> >>> tagging, but because only one direction of the traffic is tagged, it
> >>> is creating a problem for us.
> >>>
> >>> Our IDS box runs two snort instances, with filters like this:
> >>>
> >>> BPF="not port 80 and not port 443"
> >>> BPF="port 80 and port 443"
> >>>
> >>> In order to see the inbound traffic, I include the "vlan" filter, like
> so:
> >>> BPF="vlan and not port 80 and not port 443"
> >>>
> >>> ...but then I *only* see inbound traffic, and not outbound.
> >>>
> [snip]
> >>> A couple of other notes:
> >>> -The platform is RHEL5.
> >>> -We are limited to one monitor session on the swtich feeding the
> sensor.
> >>>
> [snip]
> >>>
> >>> Thanks in advance.
>
>
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