Subject: IPv6 Forwarding Troubles

From: Daniel Corbe <[email-masked]>
Date: Sat, 7 Dec 2019 11:16:54 -0500

Hello All,

I'm seeing strange behavior inside an Alpine Linux VM.

I'm trying to enable IPv6 forwarding via sysctl.  In its default
configuration, Alpine is getting an IPv6 address and a gateway and I'm
able to ping6 www.google.com

I have neighbors:

# ip -6 neigh show
fe80::fc00:2ff:fe73:a13e dev eth0 lladdr fe:00:02:73:a1:3e router used
0/0/0 probes 1 STALE

I have a default gateway:

# ip -6 route list
2001:19f0:9002:1c2f::/64 dev eth0  metric 256  expires 0sec
fe80::/64 dev eth0  metric 256
default via fe80::fc00:2ff:fe73:a13e dev eth0  metric 1024  expires 0sec
ff00::/8 dev eth0  metric 256

When I do this:

# sysctl -w net.ipv6.conf.all.forwarding=1

I lose my default gateway:

# ip -6 route list
2001:19f0:9002:1c2f::/64 dev eth0  metric 256  expires 0sec
fe80::/64 dev eth0  metric 256
anycast 2001:19f0:9002:1c2f:: dev eth0  metric 0
anycast fe80:: dev eth0  metric 0
ff00::/8 dev eth0  metric 256

Now I no longer have any IPv6 connectivity.  Can anyone point me in
the right direction here?

---

From: Nico Schottelius <[email-masked]>
Date: Sat, 07 Dec 2019 19:04:24 +0100

Hey Daniel,

that is correct. The sysctl that you are looking for is accept_ra=2.

Best,

Nico

p.s.: Fell for this many, many times before...

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