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I have been fiddling with IPv6 and address lifetimes. I found out that the valid_lft attribute will make a v6-address disappear automagically, if used correctly. To extend an address' lifetime I would

ip addr change 1:2:3:4::1/112 dev eth0 valid_lft 86000

The use of ip addr change does not appear in any man-page I have access to (Debian,Ubuntu, and online) and also not in the official documentation. I found it in an article referring to an email from 2009 to the ipv6-ops mailing-list.

From what I could determine playing around, I guess one can always use ip addr change instead of ip addr add, because if an address does not exist, ip will add one, just if ip addr add was used.

Is that correct, i.e., can anybody explain what precisely ip addr change does and how it differs from ip addr add?

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