Hi Ben, I'm happy to report that my use-case is no longer relevant. I incorrectly assumed that running the Quantum dhcp agent in dom0 was preferable to running in an unprivileged domain. It still might make sense to avoid unnecessary modification of standalone tap ports, though. Despite XAPI not supporting the addition of a standalone tap, it is possible to add one directly via ovs commands.
Thanks, Maru On 2012-10-16, at 10:00 AM, Ben Pfaff <[email protected]> wrote: > On Mon, Oct 15, 2012 at 03:29:40PM -0700, Maru Newby wrote: >> I'm running XCP 1.6 (which ships with ovs 1.4.2), and noticed that >> the ovs-xapi-sync script removes data from the Interface table for a >> standalone tap. Specifically, the 'iface-id' and 'iface-status' >> keys are removed from external-ids if a tap does not have a >> corresponding vif. Reviewing the script, it is not obvious why this >> modification is required. > > It's because we've never seen a standalone tap device under XCP at > Nicira. Standalone vifs, sure, but I was under the impression that > XenServer/XCP never created a tap without a vif. You are correct, XS/XCP never creates a tap without a vif. Creating a standalone tap is possible, though, by manually adding a port to a bridge. >> For background, I'm trying to run Devstack+Quantum under XCP, and >> specifically the Quantum dhcp agent running under dom0. This >> requires adding a standalone tap port on the Quantum bridge and >> running a dhcp server on that port. Then Quantum (specifically the >> L2 agent) needs to be able to identify the tap port via the iface-id >> so as to be able to apply a vlan tag to limit the scope of the dhcp >> server. Identification of the port is not possible if the iface-id >> is cleared by the sync script. > > So what causes the tap to be standalone? Does XCP 1.6 never create > vif/tap pairs, only a vif or a tap? Is this DHCP agent a special case > somehow? Does the DHCP agent run in a VM? (And if not, where does > the iface-id come from?) The tap is added by the Quantum dhcp agent directly, without going through XAPI (since XAPI doesn't allow creation of a standalone tap). It is a special case - the tap is to enable a dhcp server in to dom0 to interface directly with a bridge. The iface-id is set by the dhcp agent to allow the dynamic addition of a vlan tag to the port in question by the Quantum l2 agent. _______________________________________________ discuss mailing list [email protected] http://openvswitch.org/mailman/listinfo/discuss
