ifdown interface not configured (Debian 6)

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http://serverfault.com – My server is dedicated (non-virtual). I want to have 3+1 static IPs. I used aliases (eth0:0, eth0:1) previously, but read that this method is deprecated. So I added another IP and reconfigured my interface with ifup/ifdown while I'm at i;, but ifdown tells me that the interface is not configured. /etc/network/interfaces looks like this: auto lo eth0 iface lo inet loopback # Main IPs (IPv4 + IPv6) allow-hotplug eth0 iface eth0 inet static address 81.x.x.x netmask broadcast 81.x.x.255 gateway 81.x.x.1 iface eth0 inet6 static address 2a02: (HowTos)