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DragonFly bugs List (threaded) for 2011-04
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Re: ssh + IPV6 + bridge => connection freezes

From: "Steve O'Hara-Smith" <steve@xxxxxxxxxx>
Date: Sun, 24 Apr 2011 20:10:18 +0100


	Forgot to mention - IPv6 connections to the vkernels attached to
the bridge work fine.

On Sun, 24 Apr 2011 11:04:30 -0700 (PDT)
Matthew Dillon <dillon@apollo.backplane.com> wrote:

> :	Hi,
> :
> :	If IPV6 is enabled on a box and a bridge interface is enabled on
> :the same interface then any ssh connection to the box using the IPv6
> :address will freeze after a little activity (30 seconds of typing random
> :commands seems to be enough), bringing the bridge down with ifconfig will
> :restore activity to the ssh sessions (left alone they time out). I have
> seen :this with both 32 and 64 bit systems using up to date master code.
> :
> :	I'm also not sure that it's appropriate for a bridge interface to
> :have an IPv6 link local address - perhaps this is connected.
> :
> :-- 
> :Steve O'Hara-Smith                          |   Directable Mirror Arrays
>     This is probably an issue with the MAC learning for the bridge.
>     IPV6 works differently than IPV4, I think the MAC is built into
>     the IPV6 address and there's no interface ARP (not sure though).
>     We would need to explicitly support that in the bridge code.
>     The reason it works for 30-seconds is probably due to the bridge's
>     auto-learning.  When the bridge doesn't know how to route a packet
>     it basically just broadcasts it.  It is probably learning the wrong
>     thing, thinks it knows how to route the packet, but is not actually
>     routing it to the right place.  You can test this by issuing a bridge
>     flush command with ifconfig (man bridge), then determine if bridging
>     works again for a little bit.  That isn't optimal since it's
>     broadcasting in that state, so we will have to figure out the correct
>     solution.
>     Another problem is the MAC munging the bridge does.  When you connect
>     an interface to a bridge *all* packets sent from that interface use
>     the bridge's MAC address (otherwise there would be mass confusion).
>     IPV6 is probably circumventing this by pulling the MAC out of the IPV6
>     address (which is initially formed using the interface MAC) instead
>     of using the interface MAC.
> 					-Matt
> 					Matthew Dillon 
> 					<dillon@backplane.com>

Steve O'Hara-Smith                          |   Directable Mirror Arrays
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