I'm new to Linux so please bear with me...

I have a server with Intel Pro 100 dual NIC. Running Sarge 3.1

I'm trying to use one port for general access and the other for monitoring - trouble is although everything appears separate, I'm seeing the second card with the same mac as the first card. Bizarre. It's almost like they are teamed somehow. The first card (1.47) works fine - the second (1.48) doesn't

Interfaces file (I've forced the mac addresses in - not required)
# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
auto eth0
iface eth0 inet static
name Ethernet LAN card1
address 10.100.1.47
netmask 255.255.0.0
broadcast 10.100.255.255
network 10.100.0.0
gateway 10.100.2.2
dns-nameservers 194.6.79.162
hwaddress ether 00:50:8B:E2:CF:A3


# The secondary network interface
auto eth1
iface eth1 inet static
name Ethernet LAN card2
address 10.100.1.48
netmask 255.255.0.0
broadcast 10.100.255.255
network 10.100.0.0
gateway 10.100.2.2
hwaddress ether 00:50:8B:E2:CF:A2

:~# mii-tool
eth0: negotiated 100baseTx-FD, link ok
eth1: negotiated 100baseTx-FD, link ok

ifconfig:
eth0 Link encap:Ethernet HWaddr 00:50:8B:E2:CF:A3
inet addr:10.100.1.47 Bcast:10.100.255.255 Mask:255.255.0.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:7775688 errors:0 dropped:0 overruns:0 frame:0
TX packets:67671 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:3484734489 (3.2 GiB) TX bytes:11906177 (11.3 MiB)
Interrupt:17 Base address:0x3000 Memory:c6fff000-c6fff038

eth1 Link encap:Ethernet HWaddr 00:50:8B:E2:CF:A2
inet addr:10.100.1.48 Bcast:10.100.255.255 Mask:255.255.0.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:461777 errors:0 dropped:0 overruns:0 frame:0
TX packets:13 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:217627930 (207.5 MiB) TX bytes:1162 (1.1 KiB)
Interrupt:24 Base address:0x3040 Memory:c6dff000-c6dff038

part of dmesg:
e100: eth0 NIC Link is Up 100 Mbps Full duplex
e100: eth1 NIC Link is Up 100 Mbps Full duplex
device eth0 entered promiscuous mode

I have nTop and MRTG installed - I assume this is why eth0 is promiscuous. Could nTop be the cause?

cards are connected to different (Cisco Cat) switches but the second card shows this at the switch:
0060.fb60.3ae2 Dynamic 1 FastEthernet0/7
0060.fb60.3ae3 Dynamic 1 FastEthernet0/7

Puzzled I am......

So you are learning the MAC of eth0 and eth1 on the CAT port that eth1 is connected to? Thats bizzarre. The only way that should happen is if you've bridged the two ports together.

You haven't have you?

Thanks for the confirmation that it's bizarre - that alone makes me feel better.

I'm a newbie - I've no idea if it's bridged didn't do it intentionally. The second nic initially had no configuration attached - I entered details manually.

How do I check if bridged?