Re: AW: AW: AW: [vserver] Using loopback for guest-guest and guest-host communication but still remapping

From: Gordan Bobic <>
Date: Wed 29 Feb 2012 - 14:03:55 GMT
Message-ID: <>

Fiedler Roman wrote:
>> -----Ursprüngliche Nachricht-----
>> Von: Gordan Bobic []
>> Fiedler Roman wrote:
>>>> -----Ursprüngliche Nachricht-----
>>>> Von: Gordan Bobic []
>>>> Fiedler Roman wrote:
>>>>>> -----Ursprüngliche Nachricht-----
>>>>>> Von: Gordan Bobic []
>>>>>>> Fiedler Roman wrote:
>>>>>>> ....
>>>>>>> I'm trying to configure networking on a machine, where we cannot use
>> any
>>>>>>> private network for internal communication because I might need to
>> receive
>>>>>>> traffic from that network. So I can only use loopback, one private IP-
>> Range IP
>>>>>>> (server external IP) and I do not want to grab one public IP-range for
>> internal
>>>>>>> communication if avoidable.
>>>> ....
>>>>> Connect from guest to is still remapped to, which
>> is
>>>>> guest itself. So no connection to host via lo possible.
>>>> You are using 127/8 subnet on the dummy device - that won't work. You
>>>> need a non-loopback IP range on the dummy interface, e.g. 192.168/16.
>>> Thanks for your reply. I already used configuration with non-127 dummy
>> interface
>>> and they are working. In current use case (description above), I have the
>> problem,
>>> that organization cannot tell me, which private network is not in use at their
>>> location. Since I cannot handle requests from their network if I bind IPs to
>> local
>>> interface, I was trying to do it without need of any other IPs than from range
>> That is most unfortunate, but I don't see a workaround - they will have
>> to find a suitable small private subnet in 10/8, 172.16/12 or 192.168/16
>> that you can use. But since that subnet will never be routable outside
>> the machine itself, you can re-use it on all similar servers.
>>> Things I could try:
>>> ...
>>> * Use iptables mangle or nat and mark to remap external requests from IP-
>> Range also bound to local interface.
>> Sorry, not sure I quite follow what you think you can do here. Can you
>> elaborate?
> When I have some client with IP x accessing the machine and machine knows IP x on dummy interface, routing table entry to dummy interface will be used for e.g. tcp response packets, thus sending them to nirvana.
> If I mark connections depending on the interface, I should be possible to do policy routing, thus sending responses to connections from external-x back via external interface, while keeping internal-x connections internal.

That gets quite hairy. Much better to just use a routable non-dedicated
subnet. As I mentioned in my previous email, you should be able to use
the link-local subnet for this sort of thing.

Received on Wed Feb 29 14:04:03 2012

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