[Openstack-operators] ML2/OVS odd GRE brokenness

Jonathan D. Proulx jon at csail.mit.edu
Wed Nov 9 14:51:23 UTC 2016

Also I have restarted openvswitch-agent on both sides of the broken
link and it made no difference...

On Tue, Nov 08, 2016 at 05:43:27PM -0500, Jonathan Proulx wrote:
:I have an odd issue that seems to just be affecting one private
:network for one tenant, though I saw a similar thing on a different
:project network recently which I 'fixed' by rebooting the hypervisor.
:Since this has now (maybe) happened twice I figure I should try to
:understand what it is.
:Given the following four VMs on 4 different hypervisors
:vm1 on Hypervisor1
:vm2 on Hypervisor2
:vm3 on Hypervisor3
:vm4 on Hypervisor4
:vm1 -> vm3 talk fine among themselves but none to 4
:examining ping traffic transiting from vm1-vm4 I can see arp requests
:and responses at vm4 and GRE encapsulated ARP responses on
:Hypervisor1's physical interface.
:They look the same to me (same ecap id) coming in as the working vms
:traffic, but they never make it to the qvo device which is before
:iptables sec_group rules are applied at the tap device.
:attempting to tare down and recreate this resuls in the same first 3
:work last one doesn't split (possibly becuase scheduler puts them in
:the same place? haven't checked) 
:ovs-vsctl -- set Bridge br-int mirrors=@m  -- --id=@snooper2 get Port snooper2  -- --id=@gre-801e0347 get Port gre-801e0347 -- --id=@m create Mirror name=mymirror select-dst-port=@gre-801e0347 select-src-port=@gre-801e0347 output-port=@snooper2
:tcpdump -i snooper2 
:Only sees ARP requests but no response, what's broken if I can see GRE
:encap ARP responses on physical interface but not on gre-<hex>
:interface?  And why is it not broken for all tunnels endpoints?
:Oddly if I boot a 5th VM on a 5th hypervisor it can talk to 4 but not 1-3 ...
:hypervisors are Ubuntu 14.04 running Mitaka from cloud archive w/
:xenial-lts kernels (4.4.0)

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