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This turns out to a not well documented bug in the CentOS7.7 kernel that causes exactly nat rules not to run as I was seeing. Oh dear god was this nasty as whatever to find and workaround.

-- 
Computer Architect


> On Jan 4, 2020, at 10:39, Jon Masters <jcm at jonmasters.org> wrote:
> 
> Excuse top posting on my phone. Also, yes, the namespaces are as described. It’s just that the (correct) nat rules for the qrouter netns are never running, in spite of the two interfaces existing in that ns and correctly attached to the vswitch.
> 
> -- 
> Computer Architect
> 
> 
>>> On Jan 4, 2020, at 07:56, Sean Mooney <smooney at redhat.com> wrote:
>>> 
>>> On Sat, 2020-01-04 at 10:46 +0100, Slawek Kaplonski wrote:
>>> Hi,
>>> 
>>> Is this qrouter namespace created with all those rules in container or in the host directly?
>>> Do You have qr-xxx and qg-xxx ports from br-int in this qrouter namespace?
>> in kolla the l3 agent should be running with net=host so the container should be useing the hosts
>> root namespace  and it will create network namespaces as needed for the different routers.
>> 
>> the ip table rules should be in the router sub namespaces.
>> 
>>> 
>>>>> On 4 Jan 2020, at 05:44, Jon Masters <jcm at jonmasters.org> wrote:
>>>> 
>>>> Hi there,
>>>> 
>>>> I've got a weird problem with the neutron-l3-agent container on my deployment. It comes up, sets up the iptables
>>>> rules in the qrouter namespace (and I can see these using "ip netns...") but traffic isn't having DNAT or SNAT
>>>> applied. What's most strange is that manually adding a LOG jump target to the iptables nat PRE/POSTROUTING chains
>>>> (after enabling nf logging sent to the host kernel, confirmed that works) doesn't result in any log entries. It's as
>>>> if the nat table isn't being applied at all for any packets traversing the qrouter namespace. This is driving me
>>>> crazy :)
>>>> 
>>>> Anyone got some quick suggestions? (assume I tried the obvious stuff).
>>>> 
>>>> Jon.
>>>> 
>>>> -- 
>>>> Computer Architect
>>> 
>>> — 
>>> Slawek Kaplonski
>>> Senior software engineer
>>> Red Hat
>>> 
>>> 
>>