Cannot assign requested address

Bernhard Schmidt berni at
Fri May 1 17:43:36 CEST 2009

Hi Leo,

> We are trying to set up services using home-brewed scripts to set-up
> ipv6 adresses and bind services to them, just as we do this for ipv4.
> Using a fairly recent linux kernel (, or any other linux
> kernel I can get my hands on, the following scripts fails:
> ip -f inet6 a add ::2/128 dev eth0 && nc -l ::2 1234
> nc: Cannot assign requested address
> An EADDRNOTAVAIL is issued.
> Basically, we set up an ipv6 address and let nc listen on it.
> Introducing a 2 sec. sleep between setting up the interface and
> bind()'ing to it, seems to be the only workaround I have found.

You are most probably hit by Duplicate Address Detection as defined in 
RFC2462 Section 5.4. You will probably see the address being "tentative" 
in ip -6 addr while the DAD is run.

You can disable DAD on the interface setting the sysctl variable 
net.ipv6.conf.et0.dad_transmits to 0, or enable the optimistic DAD 
support (RFC4429) in recent Linux kernels.


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