netdev - Re: [PATCH net-next] net: bridge: do not send arp replies if src and target hw addr is the same

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Message-ID: <2b3bbe3a-6796-458c-88f9-1458a449d79c@blackwall.org>
Date: Tue, 9 Jan 2024 14:02:02 +0200
From: Nikolay Aleksandrov <razor@...ckwall.org>
To: Felix Fietkau <nbd@....name>, Paolo Abeni <pabeni@...hat.com>,
 netdev@...r.kernel.org
Subject: Re: [PATCH net-next] net: bridge: do not send arp replies if src and
 target hw addr is the same

On 09/01/2024 13:58, Felix Fietkau wrote:
> On 09.01.24 12:36, Paolo Abeni wrote:
>> On Thu, 2024-01-04 at 15:25 +0100, Felix Fietkau wrote:
>>> There are broken devices in the wild that handle duplicate IP address
>>> detection by sending out ARP requests for the IP that they received from a
>>> DHCP server and refuse the address if they get a reply.
>>> When proxyarp is enabled, they would go into a loop of requesting an address
>>> and then NAKing it again.
>>
>> Can you instead provide the same functionality with some nft/tc
>> ingress/ebpf filter?
>>
>> I feel uneasy to hard code this kind of policy, even if it looks
>> sensible. I suspect it could break some other currently working weird
>> device behavior.
>>
>> Otherwise it could be nice provide some arpfilter flag to
>> enable/disable this kind filtering.
> 
> I don't see how it could break anything, because it wouldn't suppress non-proxied responses. nft/arpfilter is just too expensive, and I don't think it makes sense to force the use of tc filters to suppress nonsensical responses generated by the bridge layer.
> 
> - Felix
> 

I also share Paolo's concerns, and I don't think such specific policy
should be hardcoded in the bridge. It can already be achieved via tc/nft/ebpf
as mentioned. Also please CC bridge maintainers for bridge patches, I saw this
one because of Paolo's earlier reply.

Thanks,
 Nik