Re: [PATCH dpdk v2] net: ipv6 link local compliance with rfc 4291

["Robin Jarry" <rjarry@redhat.com>]

Thomas Monjalon, Nov 19, 2025 at 01:27:
> After checking with Stephen, it appears that XOR is really desired.
> This bit must be inverted, so 0 is local and 1 is universal.
>
> Adding this comment in the code to avoid confusion in future:
>     /*
>      * The "u" bit (universal/local bit in IEEE EUI-64 terminology)
>      * must be inverted for IPv6 link local address.
>      * 0 means local scope, 1 means universal scope.
>      */
>
> Applied, thanks.

Thanks Thomas.

That XOR is described in the RFCs as "flipping the 'u' bit". I.e. the
bit should be 1 if the address is "global/universal" and 0 if the
address is "local/administratively configured".

Here's the corresponding code in Linux and BSD:

https://github.com/torvalds/linux/blob/v6.17/include/net/addrconf.h#L201

https://github.com/freebsd/freebsd-src/blob/release/14.3.0/sys/netinet6/in6_ifattach.c#L97

-- 
Robin

> No animals were injured.