Subject: Re: AW: AW: [vserver] Using loopback for guest-guest and guest-host communication but still remapping
From: Gordan Bobic <gordan@bobich.net>
Date: Wed, 29 Feb 2012 12:53:08 +0000

Gordan Bobic wrote:
> Fiedler Roman wrote:
>>> -----Ursprüngliche Nachricht-----
>>> Von: Gordan Bobic [mailto:gordan@bobich.net]
>>>
>>> Fiedler Roman wrote:
>>>>> -----Ursprüngliche Nachricht-----
>>>>> Von: Gordan Bobic [mailto:gordan@bobich.net]
>>>>>
>>>>>> 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 127.0.1.1:80 is still remapped to 127.0.2.1, 
>>>> 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
>> 127.0.0.0/8.
> 
> 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.

Thinking about it, you may also be able to get away with using 
169.254/24 link-local range for this - subject to your client's network 
not doing something broken with requiring that range to be routable. In 
theory it should be used only for internal or point-to-point connections.

Gordan