Сравните вывод команд ip a и ip r в том и другом режиме - что меняется?
[root@sch1041 /]# 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
2: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN qlen 1000
link/ether 00:1d:92:3d:87:bc brd ff:ff:ff:ff:ff:ff
inet 10.134.203.205/25 brd 10.134.203.255 scope global eth1
3: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN qlen 1000
link/ether 00:00:1e:00:04:8b brd ff:ff:ff:ff:ff:ff
inet 192.168.20.50/24 brd 192.168.20.255 scope global eth0
4: eth2: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN qlen 1000
link/ether 00:e0:4c:65:0a:b4 brd ff:ff:ff:ff:ff:ff
5: pan0: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN
link/ether ba:5e:2e:82:2b:78 brd ff:ff:ff:ff:ff:ff
6: vboxnet0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN qlen 1000
link/ether 0a:00:27:00:00:00 brd ff:ff:ff:ff:ff:ff
[root@sch1041 /]# ip r
10.134.203.128/25 dev eth1 proto kernel scope link src 10.134.203.205 metric 1
192.168.20.0/24 dev eth0 proto kernel scope link src 192.168.20.50 metric 1
default via 192.168.20.1 dev eth0 proto static
[root@sch1041 /]#