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Re: Networking Q concerning /etc/network/interfaces

On Sat 11 Feb 2012 at 17:29:25 -0500, Harry Putnam wrote:

> A little more to the story is that the address shown in ifconfig -a
> for eth0 ( is ping-able from around the network.

That's ok.

> There is only 1 ethernet wire connected to the machine and no
> wireless, so both addresses must be on the remaining nic. (eth1)

That's not ok. The conclusion is incorrect.

> Example:
> (The subject host is localhost)
> from host b (a physical machine on the lan) I can ping the above
> address (...54) or ssh to it, and arrive on localhost.


> Ditto for the actual real address (...42).
> and hostname -i shows:

hostname(1) advises against using the -i option. Not that it matters too
much, but is in your /etc/hosts?

> So, it seems there is no way around thinking both addresses are on a
> single nic since there is only one ethernet wire attached to
> localhost.

As above; erroneous. Find out about MAC addresses and ARP. They are
basic to communication on an ethernet network and will help you see a
way round your thinking.

When pinging, host b sends an ARP broadcast to all machines asking: 'any
of you out there know about the IP address' eth1 is aware isn't its address but, being conscientious, asks about on
the machine it lives on. eth0 says: 'hey that's me!'. eth1 then tells
host b: 'I've found what you are looking for,'s traffic can
be sent to first.'

Two addresses on two interfaces. ifconfig says as much too.

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