Testing Ethernet Ports

[Will Maier]

On Thu, Sep 01, 2005 at 10:36:04AM -0400, Ames, Jonathan (N-ENSCO) wrote:
> Can someone give me a hand with this?

Here goes...

> A PC has two ethernet ports, both directly on the motherboard.
> Can I connect them externally with an ethernet cable and ping from
> one port to the other to test them both?  How?

Lemme see if I parsed your question correctly:
    * box.A.nic.1 --cable--> box.A.nic.2

Is that what you're talking about? Sure. Use a crossover cable,
assign each interface a different IP on the same subnet (eg 10.0.0.1
and 10.0.0.2) and ping from one to the other:

    $ ping 10.0.0.1

Just as I can ping my (one) network interface from the box it's
running on, you can ping each of them. 

To be sure that packets are going from one interface to the other,
try the following (untested but based off `man ping`):
    
    $ ping -S 10.0.0.1 10.0.0.2

That'll ping from (-S) 10.0.0.1 to 10.0.0.2. Or, if you really want
to be sure...

    $ traceroute -s 10.0.0.1 10.0.0.2

That'll also show you the route taken by the packets, although I
don't expect that to be *too* much help (in this scenario), as there
aren't really any devices between the interfaces. Still, it can be a
handy trick.

> Another PC has the two ports listed above, plus an additional
> ethernet port in a PCI card.  Can I connect externally with the
> same cable from any port to any port to test them?  How?

So...
    * box.A.nic.1 --cable--> box.B.nic.3
    * box.A.nic.2 --cable--> box.B.nic.2
    ...etc...

See above.

> Any help will be really appreciated.  Thanks.

What is it you're actually trying to do? Something more than ping
yourself, I imagine...

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