How to list all physically installed Network Cards (Debian)

lspci | grep Ethernet

You can use lshw to see all devices on a machine. To view just the network devices enter:

lshw -class network


For Ethernet:

ls -d /sys/class/net/eth* | wc -l


/proc/net/dev file has details on all interfaces. e.g.

$ cat /proc/net/dev
Inter-|   Receive                                                |  Transmit
 face |bytes    packets errs drop fifo frame compressed multicast|bytes    packets errs drop fifo colls carrier compressed
    lo:    3562      60    0    0    0     0          0         0     3562      60    0    0    0     0       0          0
 wlan0: 2491781197 2034240    0    0    0     0          0         0 261797069 1502752    0    0    0     0       0          0
  eth0:       0       0    0    0    0     0          0         0        0       0    0    0    0     0       0          0


To list all interfaces use

/sbin/ifconfig -a

ip link show will list everything that looks like a network interface.
 
modprobe -c |grep 'eth[0-9]'

shows the real device driver in use for each ethernet device