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: <88e2f7747f9692d1585d84a4c75a46590b9e76c9.camel@redhat.com>
Date: Tue, 09 Jan 2024 13:14:52 +0100
From: Paolo Abeni <pabeni@...hat.com>
To: Felix Fietkau <nbd@....name>, netdev@...r.kernel.org, Nikolay
 Aleksandrov <razor@...ckwall.org>
Subject: Re: [PATCH net-next] net: bridge: do not send arp replies if src
 and target hw addr is the same

On Tue, 2024-01-09 at 12:58 +0100, 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, 

FTR, I don't either. But I've been surprised too much times from
extremely weird expectations from random devices, broken by "obviously
correct" behaviors change.

> 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.

Then what about adding a flag to enable/disable this new behavior?

Cheers,

Paolo