Message-ID: <56193d41-c974-cca5-3391-7e0e68c25467@ipik.org>
Date: Mon, 11 Jul 2022 09:11:03 +0200
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Subject: Re: IPv6 firewall blocking router advertisements
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To: "W. Michael Petullo" <mike@flyn.org>, Jakub Jirutka <jakub@jirutka.cz>
Cc: ~alpine/users@lists.alpinelinux.org
References: <YstKuMf89j67CIfO@imp.flyn.org>
 <7a1d4e10-02c8-7e48-9e6f-31979f28ed69@jirutka.cz>
 <Ysuc3KIlEuzwzOHa@imp.flyn.org>
From: macmpi <spam@ipik.org>
In-Reply-To: <Ysuc3KIlEuzwzOHa@imp.flyn.org>
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> I hope to experiment tomorrow to reach a stronger conclusion. Until then,
> I would appreciate any input as to why dhcpcd seems to have fixed things
> without turning off forwarding.

Actually, there seem to be some issues with dhcpcd and IPv6.
In default situations where only IPv4 interfaces are declared on
/etc/network/interfaces, with no IPv6 stances:
auto lo
iface lo inet loopback

auto eth0
iface eth0 inet dhcp

auto wlan0
iface wlan0 inet dhcp

One can note IPv6 addresses are still being acquired as ip a shows, and
IPv4 networking gets into troubles (lots of erratic interruptions,
particularly noticeable in streaming applications on wifi). It seems
like IPv6 (probably failing if not supported by router or sth) takes
some precedence and keeps altering IPv4 networking.
Disabling IPv6:
sysctl -w net.ipv6.conf.eth0.disable_ipv6=1
sysctl -w net.ipv6.conf.wlan0.disable_ipv6=1
fixes the problem.

This might probably plead for some issues in default IPv6 routing
priorities & fallback.
One could also argue IPv6 addressing should not be started altogether
unless explicitly specified in /etc/network/interfaces stances [1].
Last, setup-interfaces could ask if IPv6 shall be enabled and set
relevant stances in /etc/network/interfaces accordingly.

Thoughts?

[1]
https://wiki.alpinelinux.org/wiki/Configure_Networking#IPv6_Stateless_Autoconfiguration