Re: IPv6: the same address can be added multiple times

[kuznet@ms2.inr.ac.ru]

Hello!

> It appears you can add _exactly_ same IPv6 address on an interface many
> times:

Yes. BTW, look here:

kuznet@dust:~ # ip -6 a ls sit0
7: sit0@NONE: <NOARP,UP> mtu 1480 qdisc noqueue
    inet6 ::127.0.0.1/96 scope host
    inet6 ::193.233.7.100/96 scope global
    inet6 ::193.233.7.100/96 scope global

I have two equal addresses inherited from one IPv4 address
on two interfaces. Nothing illegal.



> FWIW, KAME stack adds the address only once(, but BSD ifconfig(8)
> doesn't show errors when you try to do it again; just doesn't add the
> second one).

8)

> It looks like a check or two in kernel is missing, or is there some
> reasoning to this behaviour?

Well, it is one of well defined approaches (unlike KAME's one).
Alternative is to implement full set of options NLM_F_* like used
in IPv4 routing to block undefined cases. In IPv6 flags are hardwired
to NLM_F_CREATE|NLM_F_APPEND both for addresses and routes.

Alexey