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I am configuring IPv6 address in a Debian machine, and this is what I have in my interface file.

auto eth0
iface eth0 inet6 static
    pre-up modprobe ipv6
    address 2001:23:207:141:0:0:0:0
    netmask 112
    gateway 2001:23:207:129:0:0:0:0

When I run the command /etc/init.d/networking restart, then I get following error.

SIOCSIFADDR file exist...
failed to bring up eth0...
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Was that IP address already manually configured using ip/ifconfig? – Zoredache Dec 14 '11 at 17:46
@Zoredache using restart it should clear any manually configured addresses. – Chris S Dec 14 '11 at 18:03
up vote 2 down vote accepted

That gateway is in a different subnet for a /112 you can only change the last group.
A 112 bit subnet means 16 bits of host address. Each group in a IPv6 Address is 16 bits.

Also, addresses where the host portion is all 0s is not recommended as it is the network ID.

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Addresses where the host portion is all 0s are not network IDs in IPv6. These addresses are predefined "Router Anycast" addresses. And yes, they are not supposed to be used as interface addresses.

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