Using 127.n.x.x/16 for namespace to host

Guenter Roeck groeck at
Mon Jul 6 17:28:42 PDT 2009

Look for ipv4_is_loopback().

Another option might be to use link local addresses.


On Mon, Jul 06, 2009 at 03:46:20PM -0700, Elwin Stelzer Eliazer wrote:
> Hi,
> I am using an internal bridge for internal socket communication between the
> host and various containers' applications.
> This is purely an internal bridge and no external traffic is expected in
> this.
> I can use a regular private ip address subnet for this, for example a
> 192.168.x.x/16 for this, and things are working.
> But since the applications at the container and host handle external traffic
> as well, we are forced to exclude this internal subnet for external use.
> Using a 127.n.x.x/16 subnet is preferred, since that is not expected to be
> used externally.
> But this is requiring kernel code change, since is programmed
> for loopback interface 'lo' in host.
> Towards this tried changing:
>      IFF_LOOPBACK 0x10 // in in.h, changed from 0x8 to 0x10
>      ifa->ifa_prefixlen = 16; // in devinet.c, changed from 8 to 16
> And still do not see them connected.
> Any suggestions on this will be appreciated.
> regards,
> Elwin.
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