Re: Asymmetric traffic/topology

[Adam Powers <apowers () lancope com>]

If when you say "Behavior-based System" you're referencing any of the
NetFlow-based products then you're not quite right.

Behavior-based NetFlow products overcome the asymmetry problem by
reassembling flows from multiple routers along disparate data paths.

If we have a situation such as:

Client -> R1 -> R2 -> R3 -> Server

Client <- R1 <- R4 <- R3 <- Server

..in this case the path is R1 to R2 to R3 in one direction and R3 to R4 to
R1 on the return path. Classic asymmetric L3 routing. NetFlow gets around
this problem because R1, R2, R3, and R4 are all sending their NetFlow
exports to a single collector where the unidirectional flows are merged and
processed into a "bi-flow" that would look more like...

Client <-> R1 <-> R2,R4 <-> R3 <-> Server

Analysis can then be performed on the bidirectional flow without fear of
asymmetry issues. All that's required is that you enable NetFlow on the
correct devices (the more the merrier IMO).




On 11/8/07 6:06 PM, "Jeremy Bennett" <jeremy () deities org> wrote:

> First there are three types of asymmetry in a network that can cause
> problems for some times of IPS devices.
>
> 1. Connection-level asymmetry: This is the case where a given TCP
> connection (up and down stream) is on a single network path but a
> separate, identical connection may follow a different path. This is
> very common and can cause problems for behavioral systems.
>
> 2. Flow-level asymmetry: This is the case where the upstream and
> downstream flows in a TCP connection may follow different paths. This
> can cause problems for behavioral systems and stateful packet-
> inspection.
>
> 3. Packet-level asymmetry: This is the case packets within a flow may
> be following different routes in a network. This can cause problems
> for any IPS except for the most basic packet-filter.
>
> Now in my experience, #1 is very common in medium to large
> enterprises that have built for scalability and redundancy. #2 is
> common in load-balanced server farms. #3 is not extremely common but
> does appear in some instances of a hot-hot redundancy deployment.
>
>
> -J
>
> On Nov 7, 2007, at 4:42 PM, snort user wrote:
>
> > Greetings.
> >
> > I am sure that most of you know about the asymmetric traffic/topology
> > problem in relevance to
> > IDS/IPS systems.
> > ( By Asymmetric traffic/topology, I mean the case where client to
> > server packets traverse a different path
> > in your network compared to server to client packets. Hence the
> > IDS/IPS see only one side of the conversation)
> >
> > I am trying to find out how wide this problem really is?
> > Is it commonly seen in large / enterprise networks ?
> >
> > Any input is welcome.
> >
> > Thanks
> >
> > ----------------------------------------------------------------------
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>
>
> ------------------------------------------------------------------------
> Test Your IDS
>
> Is your IDS deployed correctly?
> Find out quickly and easily by testing it
> with real-world attacks from CORE IMPACT.
> Go to 
> http://www.coresecurity.com/index.php5?module=Form&action=impact&campaign=intr
> o_sfw 
> to learn more.
> ------------------------------------------------------------------------


-- 

Adam  Powers
Chief Technology Officer
Lancope, Inc.
c. 678.725.1028
f. 678.302.8744
e. adam () lancope com


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Test Your IDS

Is your IDS deployed correctly?
Find out quickly and easily by testing it 
with real-world attacks from CORE IMPACT.
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to learn more.
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