netdev - Re: [net-next 08/15] net/mlx5e: CT: Preparation for offloading +trk+new ct rules

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Date:   Tue, 12 Jan 2021 11:27:04 +0200
From:   Oz Shlomo <ozsh@...dia.com>
To:     Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        Roi Dayan <roid@...dia.com>
CC:     Saeed Mahameed <saeed@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, <netdev@...r.kernel.org>,
        Paul Blakey <paulb@...dia.com>,
        Saeed Mahameed <saeedm@...dia.com>
Subject: Re: [net-next 08/15] net/mlx5e: CT: Preparation for offloading
 +trk+new ct rules



On 1/12/2021 1:51 AM, Marcelo Ricardo Leitner wrote:
> On Sun, Jan 10, 2021 at 09:52:55AM +0200, Roi Dayan wrote:
>>
>>
>> On 2021-01-10 9:45 AM, Roi Dayan wrote:
>>>
>>>
>>> On 2021-01-08 11:48 PM, Marcelo Ricardo Leitner wrote:
>>>> Hi,
>>>>
>>>> On Thu, Jan 07, 2021 at 09:30:47PM -0800, Saeed Mahameed wrote:
>>>>> From: Roi Dayan <roid@...dia.com>
>>>>>
>>>>> Connection tracking associates the connection state per packet. The
>>>>> first packet of a connection is assigned with the +trk+new state. The
>>>>> connection enters the established state once a packet is seen on the
>>>>> other direction.
>>>>>
>>>>> Currently we offload only the established flows. However, UDP traffic
>>>>> using source port entropy (e.g. vxlan, RoCE) will never enter the
>>>>> established state. Such protocols do not require stateful processing,
>>>>> and therefore could be offloaded.
>>>>
>>>> If it doesn't require stateful processing, please enlight me on why
>>>> conntrack is being used in the first place. What's the use case here?
>>>>
>>>
>>> The use case for example is when we have vxlan traffic but we do
>>> conntrack on the inner packet (rules on the physical port) so
>>> we never get established but on miss we can still offload as normal
>>> vxlan traffic.
>>>
>>
>> my mistake about "inner packet". we do CT on the underlay network, i.e.
>> the outer header.
> 
> I miss why the CT match is being used there then. Isn't it a config
> issue/waste of resources? What is CT adding to the matches/actions
> being done on these flows?
> 

Consider a use case where the network port receives both east-west encapsulated traffic and 
north-south non-encapsulated traffic that requires NAT.

One possible configuration is to first apply the CT-NAT action.
Established north-south connections will successfully execute the nat action and will set the +est 
ct state.
However, the +new state may apply either for valid east-west traffic (e.g. vxlan) due to source port 
entropy, or to insecure north-south traffic that the fw should block. The user may distinguish 
between the two cases, for example, by matching on the dest udp port.


>>
>>>>>
>>>>> The change in the model is that a miss on the CT table will be forwarded
>>>>> to a new +trk+new ct table and a miss there will be forwarded to
>>>>> the slow
>>>>> path table.
>>>>
>>>> AFAICU this new +trk+new ct table is a wildcard match on sport with
>>>> specific dports. Also AFAICU, such entries will not be visible to the
>>>> userspace then. Is this right?
>>>>
>>>>     Marcelo
>>>>
>>>
>>> right.
> 
> Thanks,
> Marcelo
>