[Oisf-devel] RFC: vlan_id in flow tracking

[Victor Julien]

On 04/08/2013 03:00 PM, Eric Leblond wrote:
> Hi,
> 
> On Mon, 2013-04-08 at 14:35 +0200, Victor Julien wrote:
>> On 04/08/2013 01:44 PM, Eric Leblond wrote:
>>> Hi,
>>>
>>> On Thu, 2013-04-04 at 13:10 +0200, Victor Julien wrote:
>>>> (RFC: request for comments :))
>>>>
>>>> Suricata currently parses VLAN headers but doesn't really do anything
>>>> with them. This is obviously wrong in some cases, like in flow tracking.
>>>> There can be several vlan's on a network, where in each we see the same
>>>> 5-tuple. These shouldn't be mixed, but right now they can be.
>>>>
>>>> This patch tries to deal with it:
>>>> https://github.com/inliniac/suricata/commit/d755fdfdc4576057712ccdb70f1e3a17bfad901c
>>>>
>>>> There are a few open issues:
>>>>
>>>> - what to do in case of multiple layers of VLAN? We should probably be
>>>> taking the tunnel approach, where we create a fake packet
>>>
>>> If people are separating client networks by using first VLAN and if
>>> second VLAN is the one used in client network, the tunneling approach
>>> will not work.
>>
>> How do you mean? Each vlan id should be a unique network, right?
> 
> Yes but I was thinking to this setup:
> 
> | Client Vlan | Network VLAN | Datagram |
> 
> If we do a tunnel and remove Client Vlan, the result is a multiclient
> packet:
> 
> | Network VLAN | Datagram |
> 
> where Network (private IP for example) may be shared among client. And
> if we have no luck, then we can cross beams and have two clients with
> same network under the same VLAN. 

Right, I think I get the point. If we would have:

[vlan 1][vlan 2][client net 1]
[vlan 2][vlan 2][client net 2]

We might mix both as we first peel off the outer vlan and then have no
way of distinguishing between the 2 client nets anymore, right?

So if we have multiple layers, we'd need multiple tags in our flow hashing?

[vlan 1][vlan 2][client net 1]
[vlan 2][vlan 2][client net 2]

Here both tag 1 and 2 would be needed to get flows for "client net 1"
and tag 2 and 2 would be needed to get "client net 2". Make sense?

In my patch I have a u16 for padding, so I could add support for dual
layer vlans easily. For more... well that would be more work. Maybe we
can just limit to 2 layers.

-- 
---------------------------------------------
Victor Julien
http://www.inliniac.net/
PGP: http://www.inliniac.net/victorjulien.asc
---------------------------------------------