[Bug 1748894] Re: intermittent dhcp failures
Launchpad Bug Tracker
1748894 at bugs.launchpad.net
Sun Feb 18 10:06:20 UTC 2018
Status changed to 'Confirmed' because the bug affects multiple users.
** Changed in: neutron (Ubuntu)
Status: New => Confirmed
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intermittent dhcp failures
Status in neutron:
Status in neutron package in Ubuntu:
Status in neutron source package in Xenial:
We have observed instances failing to get a DHCP reply, either when booting for the first time, or after a reboot.
By tcpdumping the traffic on the tap, then qvb and qvo interfaces, we can see the DHCP request leaving, but it doesn't reach the neutron-gateway node where the dhcp agent for the network runs.
If we remove and then re-add the network to the dhcp agent, it starts
working fine again.
I have dumped the output of `ovs-ofctl dump-flows br-tun` on the neutron-gateway side, before and after doing the remove/add.
One difference I noted, was a rule appearing, with the mac of the VM which had the issue:
cookie=0xb42e8d404b989e72, duration=13.344s, table=20, n_packets=0, n_bytes=0, hard_timeout=300, idle_age=13, priority=1,vlan_tci=0x0001/0x0fff,dl_dst=fa:16:3e:db:34:a3 actions=load:0->NXM_OF_VLAN_TCI,load:0x20->NXM_NX_TUN_ID,output:5201
However, this is a rule for packets from the dhcp agent to the VM, so
its absence doesn't explain why DHCP requests don't arrive to
The cloud is running neutron 8.4.0 (Mitaka), on ubuntu (16.04)
Most of the time it works, but this problem comes back often enough
that it impacts users.
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