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I have a Debian system working as a wireless router with eth0 and wlan0. Now I added an additional network manually on eth1 with ifconfig:

alix:~# ifconfig eth1 netmask
alix:~# netstat -rn
Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface         UG        0 0          0 eth0   U         0 0          0 eth1   U         0 0          0 eth0   U         0 0          0 wlan0
alix:~# ping
PING ( 56(84) bytes of data.
64 bytes from icmp_req=1 ttl=64 time=0.537 ms
64 bytes from icmp_req=2 ttl=64 time=0.199 ms
64 bytes from icmp_req=3 ttl=64 time=0.188 ms
--- ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2005ms
rtt min/avg/max/mdev = 0.188/0.308/0.537/0.161 ms

Everything works fine as you can see.

Now I would like to make the configuration permanent. Therefor I added the following section to /etc/network/interfaces:

alix:~# sed -n '/iface eth1/,/^$/p' /etc/network/interfaces
iface eth1 inet static

But when I try to start the network I get the following error:

alix:~# ifconfig eth1 down
alix:~# ifup -v eth1
Configuring interface eth1=eth1 (inet)
run-parts --verbose /etc/network/if-pre-up.d
run-parts: executing /etc/network/if-pre-up.d/hostapd
ip addr add broadcast     dev eth1 label eth1
RTNETLINK answers: File exists
Failed to bring up eth1.

When I run the ip command manually I get the same error:

alix:~# ip addr add broadcast     dev eth1 label eth1
RTNETLINK answers: File exists

What is wrong with the command? And how can I tell Debian to do the right thing?

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up vote 37 down vote accepted

Sorry but I got it myself. I had to flush the device before bringing it up:

alix:~# ip addr flush dev eth1
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I still receive a (slightly different) error RTNETLINK answers: No such process Failed to bring up eth1 BUT my Eth1 is correctly assigned now AND is UP/UP. – harperville Sep 10 '15 at 14:11

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