[Oisf-devel] RFC: vlan_id in flow tracking

[Anoop Saldanha]

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?

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

-- 
Anoop Saldanha