[kwlug-disc] Interesting NIC card behaviour

[CrankyOldBugger]

This isn't a code red problem, just something that I don't understand...

I rebuilt a server using Debian 7.8 recently.  I noticed that the two NICs
in the box are both showing the same IPv4 address, but different IPv6.  I
thought this was unusual.

Here's the breakdown:

sudo ifconfig
eth0      Link encap:Ethernet  HWaddr 1c:6f:65:41:ed:0f
          inet addr:10.42.1.120  Bcast:10.42.1.255  Mask:255.255.255.0
          inet6 addr: fe80::1e6f:65ff:fe41:ed0f/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:882643 errors:0 dropped:167406 overruns:0 frame:0
          TX packets:54750 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:208688079 (199.0 MiB)  TX bytes:14285301 (13.6 MiB)
          Interrupt:41 Base address:0x4000

eth1      Link encap:Ethernet  HWaddr f8:d1:11:c3:00:61
          inet addr:10.42.1.120  Bcast:10.42.1.255  Mask:255.255.255.0
          inet6 addr: fe80::fad1:11ff:fec3:61/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:543065 errors:0 dropped:167406 overruns:0 frame:0
          TX packets:1419 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:68916311 (65.7 MiB)  TX bytes:155332 (151.6 KiB)
          Interrupt:21 Base address:0x8000

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:34648 errors:0 dropped:0 overruns:0 frame:0
          TX packets:34648 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:11171061 (10.6 MiB)  TX bytes:11171061 (10.6 MiB)

Ideally I'd like to see one NIC handle the server's own traffic, while the
second NIC is to be used for any VMs in the box.  I'm not sure how we ended
up with both NICs showing the same IP.  I know I did try to give eth0 a
static IP but I don't understand why the settings got copied to eth1.

I opened up Network Manager and changed the name on one NIC from "Wired
Connection 1" to "eth0", but when I saved it both NICs ended up as eth0
(just in Network Manager's name.  as you see in the ifconfig above, they
still have different names there).

I suppose I could go and edit /etc/network/interfaces and hammer out two
IPs in there.  If memory serves, this would pooch Network Manager but I can
live with that.

Again, this isn't a big issue, just a strange thing that I'm trying to
understand better.
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