Re: IPv6 VIPs and deprecated flag

On Thursday, June 23, 2016, 8:52:45 PM, Ryan O'Hara wrote:
> I agree -- it is weird. Not only does the 'deprecated' flag get
> removed when the netlink reflector is triggered, but the 'nodad' flag
> remains intact. I would've guessed it would lose them both. I'll look

Deprecated isn't really a flag though. Well, it kind of is, that's how
Linux at least implements it, but you can never set it directly. The
value you set is the preferred lifetime ("ip addr show" shows it as
"preferred_lft", the underlying kernel variable is called prefered_lft
(go figure), it is the time remaining for which this address is
"preferred", that is it will be used as a potential source address for
unbound outgoing connections). If the preferred lifetime expired in
the past, deprecated automatically gets set, if the preferred lifetime
expires in the future, deprecated is automatically cleared.

You can set this manually using the preferred_lft argument to "ip addr
add/change/replace", specifying 0 for deprecated, but the default is
"forever" for manually added addresse. And any software which uses the
same underlying kernel interface can do the same of course.

The other kind of thing that can change this value automatically are
router advertisements, which if they're not actually changing your
automatically assigned prefix/address are expected to keep moving
the preferred lifetime into the future.

nodad on the other hand is definitely manual-only configuration and
should never be set automatically for a normal address. (Addresses
such as we have here that are known to be shared and thus would
definitely fail duplicate address detection don't count!)

> into the connection manager (NetworkManager) side of things, but I am
> certain that my deployment scripts disable NM -- which I've been doing
> for years.

> The VIP is definitely not the same address as the node would
> self-assigned. FYI, I am using 4 VMs under libvirt in F23 with a
> simple SLAAC setup for IPv6 address assignment. 

> Ryan


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John
-- 
Dead stars still burn


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