[PLUG] PLUG Digest, Vol 99, Issue 5

[Mike C.]

On 12/01/2012 11:27 PM, Russell Johnson wrote:

> > On Dec 1, 2012, at 12:09 PM, Mike C. <mconnors1 at gmail.com> wrote:
> >
> >> 1. Run the command  "ping 127.0.0.1" from the command line while not
> >> connected to any networks. This will test the NIC, the NIC drivers and
> the
> >> tcp/.ip stack.
> > Are you sure about that? I was under the impression that no NIC is
> required to have a loopback (127.x.x.x) network interface. It's a software
> only interface. The only thing that will test is the tcp/ip stack.
> >
> > Russell Johnson
> > russ at dimstar.net
> >
> That is my understanding as well. You always have have "localhost" ie
> loopback even with no NIC hardware installed.  This is used, for
> example, to access the CUPS printer web interface (http://localhost:631
> -This assumes you set up /etc/hosts with "127.0.0.1   localhost" during
> installation/configuration).
>
> The only way to test the NIC is to load the driver module, see if
> ifconfig seems an interface and then try to set up the interface.
>
>
>
I'm fairly certain there is some interaction with the NIC when pinging the
127.0.0.1 interface.

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:13122 errors:0 dropped:0 overruns:0 frame:0
          TX packets:13122 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:1262573 (1.2 MB)  TX bytes:1262573 (1.2 MB)

If I take down the interface with "ifdown lo" then 127.0.0.1 is not
pingable.

Localhost is just a reference to the lo network interface. Someone running
Linux on a desktop computer would have to physically remove the NIC to
verify the "no nic necessary to ping 127.0.0.1" theory.