netdev - Re: 4.14.(44->48) IPv6 RA issue?

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Date:   Mon, 18 Jun 2018 22:09:26 +0300
From:   Ido Schimmel <idosch@...sch.org>
To:     valdis.kletnieks@...edu
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: 4.14.(44->48) IPv6 RA issue?

On Mon, Jun 18, 2018 at 11:02:46AM -0400, valdis.kletnieks@...edu wrote:
> So I'm trying to troubleshoot an issue on an OpenWRT/Lede based
> router, where IPv6 connectivity totally fails. I've bisected it down to:
> 
> git log --oneline 187da94808a634477b5e5a69109ea0c566dfa64b..73d8a6ab7668173d70adbed45b61be5256c505e
> 73d8a6ab7668 (refs/bisect/bad) base-files: fix UCI config parsing and callback handling
> e52f3e9b1376 kernel: bump 4.14 to 4.14.48
> 7590c3c58f5e (HEAD) scripts: Replace obsolete POSIX tmpnam in slugimage.pl with File::Temp function
> 987900f2de76 hostapd: properly build hostapd-only SSL variants
> 
> and am pretty sure that it's the kernel bump (works with a 4.14.44 kernel,
> breaks with 4.14.48) as the other 3 commits don't go anywhere near IPv6 handling.

...

> Note that eth1 is the uplink towards my ISP.  I've pointed a 'tcpdump -n -i eth1 ip6'
> at it, and see plenty of RA packets come in, but neighbor discovery never completes.
> Looking at the Changelogs for .45->.50 don't show any smoking-gun patches.
> 
> This ring any bells, before I delve deeper into it?

If this is a router and forwarding is enabled, then you need to set
'accept_ra' to '2' [1]. Is this what you have configured? Seems that
OpenWRT recently started to explicitly set 'accept_ra' to '0' [2].

1. https://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt
2. https://github.com/openwrt/openwrt/commit/bb46520159c0119e829900e29681feea6f297fe0