[lug] physical/logical network interfaces

[Hugh Brown]

On Tue, 22 Mar 2005, Hugh Brown wrote:

> I have a couple of Dell PowerEdge 2500 that have two physical NICs.
> However when I do an lspci I show 5 ethernet adapters:
>
> lspci|grep Ethernet
>
> 00:04.0 Ethernet controller: Intel Corp. 82557/8/9 [Ethernet Pro 100] (rev
> 08)
> 01:04.0 Ethernet controller: Intel Corp. 82557/8/9 [Ethernet Pro 100] (rev
> 05)
> 01:05.0 Ethernet controller: Intel Corp. 82557/8/9 [Ethernet Pro 100] (rev
> 05)
> 04:04.0 Ethernet controller: Intel Corp. 82557/8/9 [Ethernet Pro 100] (rev
> 05)
> 04:05.0 Ethernet controller: Intel Corp. 82557/8/9 [Ethernet Pro 100] (rev
> 05)
>
> It's got Redhat Enterprise 3 on it.  Redhat found all 5 and set up aliases
> for all of them in /etc/modules.conf
>
> I configured eth1 with its own IP address separate from eth0.
>
> The weirdness is that if I run a tcpdump -i eth1 I get no traffic
> whatsoever.  If I run "tcpdump -i eth0 dst host <eth1's ip>" I see all the
> traffic that eth1 should be receiving.
>
> If I do an arp on eth0's IP address, I get the same MAC that I do from
> ifconfig.  If I do an arp on eth1's IP address, I get eth0's MAC address.
>
> Has anyone seen this behavior before?
>
> It seems like three of the above NICs in the lspci output should not exist
> and that my eth1 should actually be an eth0:0.
>
> Hugh

I always love responding to my own posts.  So there really are 5 ports,
the onboard NIC, and two Intel pro 100 dual port cards.

So the question morphs.  The four ports in the dual port cards have no
cables in them.  Only the onboard NIC is connected.  So now my conundrum
is this:

Why would the kernel allow me to configure eth1 as an interface (and
receive traffic for that interface) when there's no cable connected to it?

Is it an artifact of all of the cards using the same driver (e100)?

This strikes me as obscurely broken.

Any ideas?

Hugh