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Re: brctl setfd virbr0 0.1 by default?



> https://bugzilla.redhat.com/show_bug.cgi?id=435757
> Sometime after F8, something changed where stuff attached to a bridge  
> fails to connect until 15 seconds later.  A manual workaround of brctl  
> setfd BRIDGENAME 0.1 makes stuff work immediately.
>
> Are there any reasons why don't we do this by default for virbr0 in libvirt?
>
> Use cases:
> - Attach a different tun/tap device to the virbr0 bridge to talk to your  
> virtual machine.
> - Attach ethX real device to your vribr0 bridge to talk to your virtual  
> machine without NAT (like if you are doing DHCP.)

I would assume that brctl or the kernel became fully 802.1d Spanning 
Tree Protocol compliant.  Compliant bridges MUST delay entering the 
forwarding state at link up or initialization, transitioning between 
LISTENING and LEARNING states first.  This is required by the 
standard.

That being said, most really switches support a per-port "fast start" 
mode sometimes called "portfast" or "edge" where the port is 
designated to be connected directly to an end system rather than 
another bridge/switch, which causes the forwarding delay to be set to 
0.  This is not strictly compliant to the standard, but is often used 
because of the issue where DHCP clients will time out after 15 
seconds.


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