[Oisf-devel] RFC: vlan_id in flow tracking

[Victor Julien]

On 04/08/2013 04:45 PM, Anoop Saldanha wrote:
> On Mon, Apr 8, 2013 at 7:17 PM, Eric Leblond <eric at regit.org> wrote:
>> Hi,
>>
>> On Mon, 2013-04-08 at 15:13 +0200, Victor Julien wrote:
>>> 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?
>>
>> Exactly!
>>
>>> 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?
>>
>> Yes, this is the best behavior.
>>
>>> 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.
>>
>> From http://en.wikipedia.org/wiki/IEEE_802.1Q triple tagging is not
>> standard.
>>
>> By the way, tagging host in the same way will be needed (thinking to
>> threshold mainly).
>>
> 
> For 1 direction-only tagged packets we shouldn't consider the tag
> while computing the hash, should we?

Right, the hash will fail. Problem is that we start hashing before we
know that the other side won't have vlans.

> Maybe provide a configuration to specify ipnets, and suricata won't
> use the tag(while computing the hash) for packets matching that range?
> 

I was thinking about just doing a global switch. Do we need something
more specific?

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