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Date: Wed, 9 Nov 2022 11:55:47 -0800
From: Stephen Hemminger <stephen@networkplumber.org>
Message-ID: <20221109115547.494d5006@hermes.local>
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Subject: Re: [Bridge] How to connect more than 200 interfaces to a bridge
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To: Ali Shirvani <alishirv@protonmail.com>
Cc: Ali Shirvani via Bridge <bridge@lists.linux-foundation.org>

On Wed, 09 Nov 2022 19:25:32 +0000
Ali Shirvani <alishirv@protonmail.com> wrote:

> Sent with Proton Mail secure email.
> 
> ------- Original Message -------
> On Wednesday, November 9th, 2022 at 8:21 PM, Stephen Hemminger <stephen@networkplumber.org> wrote:
> 
> 
> > On Wed, 09 Nov 2022 10:51:27 +0000
> > Ali Shirvani via Bridge bridge@lists.linux-foundation.org wrote:
> >   
> > > Hello everyone,
> > > 
> > > It seems we reach the Linux bridge limitation on the number of interfaces in a single bridge. Currently, we have 210 tap interface in a bridge, and we suffer from more than 50% packet loss when we ping the IP address of the virtual machine that uses one of the tap interfaces in the bridge.
> > > Do you know how we can connect more than 200 VMs virtual interfaces to a bridge?
> > > 
> > > Best regards,
> > > Ali
> > > 
> > > Sent with Proton Mail secure email.  
> > 
> > 
> > The upper limit on interfaces per bridge should be 1023.
> > That limitation comes from spanning tree.
> > 
> > You might bet able to improve performance by disabling flooding to those tap devices.
> > Normally, any broadcast/unknown/multicast must be copied and flooded to each interface.  
> 
> Thanks a lot for your guidance. I disabled the spanning tree on the bridge with `brctl stp br0 off` but the issue does not resolve. Would you please elaborate more about disabling flooding on tap devices, I don't know how I should disable flooding on tap devices.

It is not a spanning tree issue, in fact STP can protect you from bad VM's.
It is more about configuring the bridge ports after setup.