Re: Problem with IPv6 privacy addresses in 7.0

[David Gibson <david@gibson.dropbear.id.au>]

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On Thu, May 28, 2026 at 05:17:11PM +0200, Stefano Brivio wrote:
> On Thu, 28 May 2026 16:34:02 +0200
> Andrew Lunn <andrew@lunn.ch> wrote:
> 
> > > Actually, an eventually fixed version of NetworkManager doesn't need to
> > > know the behaviour of the kernel: it can just order addresses by
> > > timestamps instead, as Fernando mentioned.  
> > 
> > Can pasta also use this scheme to order the addresses? Is there a way
> > pasta can be independent of the order?
> 
> pasta itself doesn't even care, it just inserts (copies) addresses one
> by one as returned. The kernel cares, because it preferentially picks
> the first one, as stored, within a given scope.
> 
> The problem is that they are inserted in the opposite order than one
> would expect (that is, opposite to what's used by the kernel to select
> them, and opposite to what's done for IPv4).
> 
> This (with an older kernel version) is quite "funny" (pasta by default
> copies everything it finds to the inner namespace):

Fwiw, a hypothetical tool which copied network configuration from one
namespace to an independent one - or which saved network configuration
to restore it later - would likely hit the same issue.

> ---
> $ pasta -6 -Ix --no-ra
> # ip a a fd00::1 dev x
> # ip a a fd43::1 dev x
> # ip a a 2620::1 dev x
> # ip link set dev x up
> # ip a s x
> 2: x: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default qlen 1000
>     link/ether 86:de:6b:53:5c:05 brd ff:ff:ff:ff:ff:ff
>     inet6 2620::1/128 scope global tentative 
>        valid_lft forever preferred_lft forever
>     inet6 fd43::1/128 scope global tentative 
>        valid_lft forever preferred_lft forever
>     inet6 fd00::1/128 scope global tentative 
>        valid_lft forever preferred_lft forever
> # pasta -6 --config-net --no-ra
> # ip a s x scope global
> 2: x: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 65520 qdisc fq_codel state UNKNOWN group default qlen 1000
>     link/ether 32:d4:5b:f0:fd:50 brd ff:ff:ff:ff:ff:ff
>     inet6 fd00::1/128 scope global nodad 
>        valid_lft forever preferred_lft forever
>     inet6 fd43::1/128 scope global nodad 
>        valid_lft forever preferred_lft forever
>     inet6 2620::1/128 scope global nodad 
>        valid_lft forever preferred_lft forever
> # pasta -6 --config-net --no-ra
> # ip a s x scope global
> 2: x: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 65520 qdisc fq_codel state UNKNOWN group default qlen 1000
>     link/ether 1a:ed:4a:27:f6:9f brd ff:ff:ff:ff:ff:ff
>     inet6 2620::1/128 scope global nodad 
>        valid_lft forever preferred_lft forever
>     inet6 fd43::1/128 scope global nodad 
>        valid_lft forever preferred_lft forever
>     inet6 fd00::1/128 scope global nodad 
>        valid_lft forever preferred_lft forever
> ---
> 
> ...at every level of namespacing, the order is swapped. Note that
> iproute2 also reports them in the order they're sent over netlink.
> 
> > Maybe we should just make the order random, so equally breaking
> > everybody, and pushing user space to not assume any order :-)
> 
> The thing is... the kernel assumes the order. :) But it also has to.
> 
> -- 
> Stefano
> 

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

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