netdev - Re: Issues during assigning addresses on point to point interfaces

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Date:   Thu, 24 Jun 2021 12:45:45 +0200
From:   Marek Behún <kabel@...nel.org>
To:     Pali Rohár <pali@...nel.org>
Cc:     netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        linux-kernel@...r.kernel.org,
        Nicolas Dichtel <nicolas.dichtel@...nd.com>,
        Andrew Lunn <andrew@...n.ch>,
        Russell King <rmk+kernel@...linux.org.uk>,
        Stephen Hemminger <stephen@...workplumber.org>,
        Phil Sutter <phil@....cc>
Subject: Re: Issues during assigning addresses on point to point interfaces

On Sun, 6 Jun 2021 17:10:08 +0200
Pali Rohár <pali@...nel.org> wrote:

> Hello!
> 
> Seems that there is a bug during assigning IP addresses on point to
> point interfaces.
> 
> Assigning just one local address works fine:
> 
>     ip address add fe80::6 dev ppp1 --> inet6 fe80::6/128 scope link
> 
> Assigning both local and remote peer address also works fine:
> 
>     ip address add fe80::7 peer fe80::8 dev ppp1 ---> inet6 fe80::7
> peer fe80::8/128 scope link
> 
> But trying to assign just remote peer address does not work. Moreover
> "ip address" call does not fail, it returns zero but instead of
> setting remote peer address, it sets local address:
> 
>     ip address add peer fe80::5 dev ppp1 --> inet6 fe80::5/128 scope
> link
> 

Adding some other people to Cc in order to get their opinions.

It seems this bug is there from the beginning, from commit
caeaba79009c2 ("ipv6: add support of peer address")
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=caeaba79009c2

Maybe some older user-space utilities use IFA_ADDRESS instead of
IFA_LOCAL, and this was done in order to be compatible with them?

Marek