[PVE-User] Solved proxmox KVM VNC problem / issue

StalkR stalkr at gmail.com
Tue Feb 8 13:23:46 CET 2011

Hello Jesper,

Glad to see I'm not the only one to have this problem.
I don't see any side effect of disabling IPv6 on eth0, since as you
said IP address is carried by vmbr0.
So, good finding, thanks!


On Tue, Feb 8, 2011 at 12:24, Jesper Dangaard Brouer <jdb at comx.dk> wrote:
> Hi Proxmox users
> I have (hopefully) identified the problem, with proxmox, where the "Open
> VNC console" does NOT work for KVM virtual machines, but it works for
> OpenVZ containers.
> The problem is related to IPv6 socket bindings, which has been up on the
> mailing list before see [1] and [2], and via a blog [3].
> The real cause of the problem is that eth0 gets assigned an IPv6 address
> automatically (related to its MAC).  The interface eth0 is part of a
> bridge, and thus must not be assigned any IPs (due to, how the kernel
> bridge code works, one must use the bridge interface vmbr0).  Somehow
> the netcat/nc choose to bind to this address and screws up.
> My solution was to disable IPv6 on eth0
> via /proc/sys/net/ipv6/conf/eth0/disable_ipv6.  This can be done via the
> commands:
>  echo "net.ipv6.conf.eth0.disable_ipv6 = 1" > /etc/sysctl.conf
>  sysctl -p
> One of the reasons eth0 gets assigned an IPv6, is most likely because,
> the default install is missing a line in /etc/network/interfaces.  The
> file should contain:
>  iface eth0 inet manual
> This line will propably also solve the issue.
> System:
>  Problem found on a freshly installed Proxmox version 1.7
> Links:
>  [1] http://pve.proxmox.com/pipermail/pve-user/2010-February/001236.html
>  [2] http://pve.proxmox.com/pipermail/pve-user/2010-February/001237.html
>  [3] http://blog.stalkr.net/2010/02/proxmox-kvm-reach-vnc-in-ipv6.html
> --
> Best regards
>  Jesper Brouer
>  ComX Networks A/S
>  Linux Network Kernel Developer
>  Cand. Scient Datalog / MSc.CS
>  Author of http://adsl-optimizer.dk
>  LinkedIn: http://www.linkedin.com/in/brouer

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