Multiple Loopback Interfaces

[Neil Horman]

On Thu, Aug 29, 2013 at 08:32:56AM -0700, John Chludzinski wrote:
> Both 127.0.0.7 and 127.0.0.10 exist in /etc/hosts for the client apps to
> use when connecting to the server.    The clients use both
> gethostbyname() and getservbyname() for connecting.  Currently, there
> are *no* multiple loopback interfaces defined.  
> 
> I wrote my own example TCP socket code to test the set up and found
> problems.
> 
What problems?

> Without defining multiple loopback interfaces using 127.0.0.7 and
> 127.0.0.10, are 127.0.0.7 and 127.0.0.10 simply the same interface?
> 
Yes.

> BTW, this is code I inherited.
> 
> ---John
> 
> 
> On Thu, Aug 29, 2013, at 06:49 AM, Reindl Harald wrote:
> > BTW:
> > 
> > try to ping 127.0.0.1, 127.0.0.2, 127.0.0.3............
> > 
> > here they are pingable as default
> > 
> > the instruction below if only needed if the application
> > checks that a configured IP exists via ifconfig or lookalike
> > 
> > Am 29.08.2013 15:46, schrieb Reindl Harald:
> > > Am 29.08.2013 15:38, schrieb John Chludzinski:
> > >> I need to used multiple loopback addresses (interfaces) for an server
> > >> application that communicates with multiple clients running on the same
> > >> machine.  Since a loopback interface short circuits the network stack
> > >> (looping back in the IP layer) it is a more efficient means of
> > >> communication, hence better for my purpose.
> > >>
> > >> How do I define multiple loopback interfaces?
> > >>
> > >> BTW, I'm a newbie to this mailing mailing list.  Hopefully this is an
> > >> appropriate question?
> > > 
> > > if you are running network.service it's trivial
> > > NetworkManager -> no ida, i do not touch it
> > > ___________________________________________
> > > 
> > > [root at rh:/etc/sysconfig/network-scripts]$ cat /etc/sysconfig/network-scripts/ifcfg-lo:1
> > > DEVICE=lo:1
> > > IPADDR=127.0.0.2
> > > ONPARENT=yes
> > > 
> > > [root at rh:/etc/sysconfig/network-scripts]$ ifup lo:1
> > > 
> > > [root at rh:/etc/sysconfig/network-scripts]$ ifconfig lo:1
> > > lo:1: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536
> > >         inet 127.0.0.2  netmask 255.0.0.0
> > >         loop  txqueuelen 0  (Lokale Schleife)
> > > 
> > > [root at rh:/etc/sysconfig/network-scripts]$ ping 127.0.0.2
> > > PING 127.0.0.2 (127.0.0.2) 56(84) bytes of data.
> > > 64 bytes from 127.0.0.2: icmp_seq=1 ttl=50 time=0.056 ms
> > > ___________________________________________
> > > 
> > > that's the "lo" config shipped with Fedora
> > > 
> > > [root at rh:/etc/sysconfig/network-scripts]$ cat /etc/sysconfig/network-scripts/ifcfg-lo
> > > DEVICE=lo
> > > IPADDR=127.0.0.1
> > > NETMASK=255.0.0.0
> > > NETWORK=127.0.0.0
> > > # If you're having problems with gated making 127.0.0.0/8 a martian,
> > > # you can change this to something else (255.255.255.255, for example)
Alternatively you can set /proc/net/ipv4/conf/l0/route_localnet to true