konkrétní reálný případ, dvě síťovky, jedna s přístupem na internet, druhá jen interní síť, obě dhcp, Kubuntu:
mkiklhorn@admin3:~$ uname -a
Linux admin3 2.6.35-25-generic #44-Ubuntu SMP Fri Jan 21 17:40:44 UTC 2011 x86_64 GNU/Linux
mkiklhorn@admin3:~$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 10.10
Release: 10.10
Codename: maverick
mkiklhorn@admin3:~$ cat /etc/network/interfaces
auto lo
iface lo inet loopback
auto eth0
iface eth0 inet manual
up ifconfig $IFACE 0.0.0.0 up
up ip l s $IFACE promisc on
down ip l s $IFACE off
down ifconfig $IFACE down
auto br0
iface br0 inet dhcp
bridge_ports eth0 tap0
up route add -net 224.0.0.0/4 dev br0
auto eth1
iface eth1 inet dhcp
mkiklhorn@admin3:~$ ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue state UNKNOWN
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,PROMISC,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN qlen 1000
link/ether 1c:6f:65:3d:70:8a brd ff:ff:ff:ff:ff:ff
inet6 fe80::1e6f:65ff:fe3d:708a/64 scope link
valid_lft forever preferred_lft forever
3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN qlen 1000
link/ether 1c:6f:65:3d:70:7a brd ff:ff:ff:ff:ff:ff
inet 172.20.1.61/24 brd 172.20.1.255 scope global eth1
inet6 fe80::1e6f:65ff:fe3d:707a/64 scope link
valid_lft forever preferred_lft forever
4: br0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN
link/ether 1c:6f:65:3d:70:8a brd ff:ff:ff:ff:ff:ff
inet 192.168.12.138/21 brd 192.168.15.255 scope global br0
inet6 fe80::1e6f:65ff:fe3d:708a/64 scope link
valid_lft forever preferred_lft forever
5: vboxnet0: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN qlen 1000
link/ether 0a:00:27:00:00:00 brd ff:ff:ff:ff:ff:ff
6: tap0: <BROADCAST,MULTICAST,PROMISC,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN qlen 500
link/ether 96:7d:1a:e9:22:a9 brd ff:ff:ff:ff:ff:ff
inet6 fe80::947d:1aff:fee9:22a9/64 scope link
valid_lft forever preferred_lft forever
mkiklhorn@admin3:~$ ip r
172.20.1.0/24 dev eth1 proto kernel scope link src 172.20.1.61
192.168.8.0/21 dev br0 proto kernel scope link src 192.168.12.138
169.254.0.0/16 dev eth1 scope link metric 1000
224.0.0.0/4 dev br0 scope link
default via 192.168.8.1 dev br0 metric 100
default via 172.20.1.140 dev eth1 metric 100