Tap0.device issues while attempting to start bridged network

Question

i'm trying to get the bridged network working so i can run xen and everytime i try sudo netctl enable xenbridge-dhcp i get this error in journalctl.
-- Logs begin at Wed 2013-05-15 14:16:16 PDT, end at Tue 2013-05-28 18:26:42 PDT. --
May 28 18:25:07 kimbra sudo[23762]: pam_unix(sudo:session): session closed for user root
May 28 18:25:12 kimbra sudo[23764]: jd : TTY=pts/1 ; PWD=/home/jd ; USER=root ; COMMAND=/usr/bin/netctl start xenbridge-dhcp
May 28 18:25:12 kimbra sudo[23764]: pam_unix(sudo:session): session opened for user root by (uid=0)
May 28 18:25:12 kimbra systemd[1]: Expecting device sys-subsystem-net-devices-tap0.device...
-- Subject: Unit sys-subsystem-net-devices-tap0.device has begun with start-up
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/li … temd-devel
-- Unit sys-subsystem-net-devices-tap0.device has begun starting up.
May 28 18:26:42 kimbra systemd[1]: Job sys-subsystem-net-devices-tap0.device/start timed out.
May 28 18:26:42 kimbra systemd[1]: Timed out waiting for device sys-subsystem-net-devices-tap0.device.
-- Subject: Unit sys-subsystem-net-devices-tap0.device has failed
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/li … temd-devel
-- Documentation: http://www.freedesktop.org/wiki/Softwar … e9d022f03d
-- Unit sys-subsystem-net-devices-tap0.device has failed.
-- The result is timeout.
May 28 18:26:42 kimbra systemd[1]: Dependency failed for xen bridge.
-- Subject: Unit netctl@xenbridge\x2ddhcp.service has failed
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/li … temd-devel
-- Documentation: http://www.freedesktop.org/wiki/Softwar … e9d022f03d
-- Unit netctl@xenbridge\x2ddhcp.service has failed.
-- The result is dependency.
May 28 18:26:42 kimbra sudo[23764]: pam_unix(sudo:session): session closed for user root
tap0.device is not working and i can't find the uml_utilities package anywhere.
help?

Answer 1

Sorry for the rather late response, but I've just been through this issue myself. The tunctl & brctl utilities are now part of 'uml_utliities', which is itself deprecated.
I downloaded uml_utilities and installed it.
I've encountered a bug which appears to be common to all bridged netwroking (the inbuilt VirtualBox bridging demonstrates the same problem). The nature of the bug is that if I bridge with the physical ethernet adapter, only a linux guest VM can see the outside world. THis is true whether the guest is running under VirtualBox or KVM so the issue appears to be generic.
Non-linux guests can see each other and the *host*, but not the rest of the world. Speculations as to the reason include the deprecation of Uml_Utilities, but regardless, I tried something different.
I created the bridge and assigned it a separate subnet. I added some tap interfaces. I ran a DHCP server instance listening on the bridge alone. I set forwarding on, and created a static route enabling my router to find the virtual subnet.
I used dnsmasq for the DHCP as it isn't used by my regular network setup, meaning that I can screw around with it trivially without breaking things. Additionally, I set up the config automatically from my vnet script. I can potentially add multiple virtual subnets this way although I haven't included support in the script as yet. The minimal config hands out addresses from the pool specified on the vnet command line, and I can set up static addresses on the same subnet by referencing the contents of /etc/host and /etc/ethers (it identifies vms by mac address).
This works perfectly, and has the advantage that the virtual network traffic will route via wireless as well as cabled ethernet. It also makes it simple to firewall the virtual subnet and reduces the risk of experiencing minor hassle when my broken vnet code stuffs the ethernet interface.
Ping me if you want a copy of the vnet script, although it's still very much a work in progress.
Last edited by salafrance (2013-09-21 20:02:12)