Simon Deziel wrote:

> On 08/21/2014 12:52 PM, Gert Doering wrote:
>> Hi,
>>
>> On Thu, Aug 21, 2014 at 05:22:28PM +0100, Ian Brooks wrote:
>>> I can see the traffic leaving the vm, hitting the internal gateway for
>>> the bridge, hit the correct tunnel to the destination server and arrive
>>> on tun0 on the destination server, but for some reason the packets arent
>>> then passed to the internal bridge network,
>>
>> Sounds like linux' rp_filter is biting you "if the packet is not supposed
>> to go there in the forward way, do not accept it on incoming".
>>
>> Look in "sysctl -a" for "rp_filter", set it to "0" for the relevant tun
>> interfaces.
> 
> Disabling rp_filter completely should do it but I'd just want to add
> that "recent" linux version also allow loose mode rp filtering that
> seems all indicated for asymmetric routing like this case.

There's another benefit to using loose mode as well because the kernel takes 
the *largest* value between the interface-specific and 'all' values. While 
the kernel default is 0, many distros set net.ipv4.conf.all.rp_filter=1 in 
startup scripts.

Using 2 on the interface allows this to be overridden without turning rp 
path protection off completely for all other interfaces.

-- 
Josh


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