Virtual NIC: "SIOCSIFFLAGS: Cannot assign requested address" but gets created

Question

I am having some trouble with the apparently easy task of creating a virtual network adapter on a physical network card in my Linux system (custom distribution, Debian-based).

If I run

ifconfig eth0:1 10.50.55.130 netmask 255.255.255.0

everything goes just fine: the virtual NIC is silently added and correctly shown by ifconfig.

I want the definition for this virtual NIC to appear in /etc/network/interfaces though. I have added the following stanza.

# virtual NIC
# auto eth0:1
iface eth0:1 inet static
    address 10.50.55.130
    netmask 255.255.255.0

First line commented out because as of now I am not interested in having the system bring the network interface up automatically.

Everything seems fine.

If I run ifup eth0:1, though, I get SIOCSIFFLAGS: Cannot assign requested address.

What I really can't wrap my head around is that the virtual NIC is actually created. Here's the output from ifconfig.

can0      Link encap:UNSPEC  HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-                        00-00-00  
      UP RUNNING NOARP  MTU:16  Metric:1
      RX packets:1206446 errors:0 dropped:0 overruns:0 frame:0
      TX packets:193280 errors:0 dropped:12 overruns:0 carrier:12
      collisions:0 txqueuelen:10 
      RX bytes:7645126 (7.2 MiB)  TX bytes:1393003 (1.3 MiB)
      Interrupt:68 

can1      Link encap:UNSPEC  HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00  
      UP RUNNING NOARP  MTU:16  Metric:1
      RX packets:299171 errors:0 dropped:0 overruns:0 frame:0
      TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
      collisions:0 txqueuelen:10 
      RX bytes:2393368 (2.2 MiB)  TX bytes:0 (0.0 B)
      Interrupt:71 

eth0      Link encap:Ethernet  HWaddr 98:5d:ad:c2:30:30  
      inet addr:10.90.100.43  Bcast:0.0.0.0  Mask:255.255.248.0
      UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
      RX packets:1560275 errors:0 dropped:1 overruns:0 frame:0
      TX packets:790 errors:0 dropped:0 overruns:0 carrier:0
      collisions:0 txqueuelen:1000 
      RX bytes:96964255 (92.4 MiB)  TX bytes:176882 (172.7 KiB)
      Interrupt:56 

eth0:1    Link encap:Ethernet  HWaddr 98:5d:ad:c2:30:30 
      inet addr:10.50.55.130  Bcast:10.50.55.255  Mask:255.255.255.0
      UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
      Interrupt:56 

eth1      Link encap:Ethernet  HWaddr 98:5d:ad:c2:30:32  
      inet addr:169.254.8.141  Bcast:169.254.255.255  Mask:255.255.0.0
      UP BROADCAST MULTICAST  MTU:1500  Metric:1
      RX packets:0 errors:0 dropped:0 overruns:0 frame:0
      TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
      collisions:0 txqueuelen:1000 
      RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

lo        Link encap:Local Loopback  
      inet addr:127.0.0.1  Mask:255.0.0.0
      inet6 addr: ::1/128 Scope:Host
      UP LOOPBACK RUNNING  MTU:65536  Metric:1
      RX packets:140932 errors:0 dropped:0 overruns:0 frame:0
      TX packets:140932 errors:0 dropped:0 overruns:0 carrier:0
      collisions:0 txqueuelen:0 
      RX bytes:8522761 (8.1 MiB)  TX bytes:8522761 (8.1 MiB)

Why am I getting this error? Or... Why does the NIC get created?

I'll add that if I invoke ifup -f eth0:1 (with the force option) no error messages are shown AND the virtual network adapter is brought up just fine.

Solution 1

ifconfig is considered obsolete these days. Try to use ip tool instead. All recent distributions should support it, it's part of iproute tool set.

If you just want additional IP address on the interface, use following command:

ip addr add 10.50.55.130/24 dev eth0

And I agree with Johan Myréen's comment bellow your question.

Solution 2

apart from command line method, the preferred method for Debian based system is to use networking configuration files.

The alias method prefers to use such order: eth0, eth:0:0, eth0:1, ...

So first alias to system would be eth0:0 and to achieve this persistent across system reboots, create a file /etc/network/interfaces.d/eth0 with such content:

auto eth0:0
allow-hotplug eth0:0
iface eth0:0 inet static
      address 10.50.55.130/24

Or you can edit directly the file /etc/network/interfaces but this is not recommended as it can be overwritten automatically.

The key is to use format of address with slash subnet, and not to use netmask keyword anymore: address 10.50.55.130/24

And of course do

service networking restart

to test the configuration. Check afterwards with command:

service networking status

and

ip address

Please note, that like mentioned in comments, the actual name of the interface can be any, thus make sure to check interface names with ip addr command and use that name and amend :0 and so on to that, like enp3s0f0:0 and enp3s0f0:1 and so on.

Comments

[Johan Myréen]

Interface names like eth0:1 do not denote separate interfaces, not even virtual ones. They are just aliases, i.e. different names for the real interface. Because they are just aliases, they don't have separate state – for example, eth0:1 can't be down if eth0is up. This alias mechanism is only needed because the old ifconfig tool can only handle one address per device name.

[Rui F Ribeiro]

More interestingly yet, in certain situations ifconfig does not show alias create with ip. +1 for the ip recommendation.

[Johan Myréen]

@RuiFRibero Try adding label eth0:1 to the ip address add ... line.

[Kojo]

I made almost the same thing for several IPs, except that in order to restart successfully networking.service, I had to replace the legacy eth0 by my new interface name enp3s0f0, even if eth0 was the one in interfaces ... `auto enp3s0f0:1 iface enp3s0f0:1 inet static address aaa.bbb.ccc.ddd/30