netdev - Re: Trying to implement secondary loopback

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Message-ID: <20130315151528.GA10503@order.stressinduktion.org>
Date:	Fri, 15 Mar 2013 16:15:28 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Thomas Martitz <thomas.martitz@....fraunhofer.de>
Cc:	richard -rw- weinberger <richard.weinberger@...il.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"edumazet@...gle.com" <edumazet@...gle.com>,
	"herbert@...dor.apana.org.au" <herbert@...dor.apana.org.au>
Subject: Re: Trying to implement secondary loopback

On Fri, Mar 15, 2013 at 04:07:32PM +0100, Thomas Martitz wrote:
> Same result. I assumed the kernel treats lo in a special way for 
> localhost-connections and that it would be impossible to achieve the 
> same with a custom interface.
> 
> I did the following:
> 
> ifconfig lo down
> insmod ./mykmod.ko
> ifconfig eth2 up
> ifconfig eth2 127.0.0.1
> 
> At this point ifconfig prints the same information for eth2 that it had 
> printed for lo before (except for the LOOPBACK flag, but I can enable 
> that one as well by adding IFF_LOOPBACK to the interface flags in the 
> module). Yet my test application only works with lo, not eth2.

127.0.0.0/8 is guarded by the kernel, but there is a sysctl for relaxing the
checks, /proc/sys/net/ipv4/conf/route_localnet. You could give it a try.

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