Bug#867590: networkd removes statically set default route when RA expires

[Michael Biebl]

Hi Marc

On Fri, 07 Jul 2017 17:52:04 +0200 Marc Haber
<mh+debian-packages at zugschlus.de> wrote:
> Package: systemd
> Version: 232-25
> Severity: normal
> Tags: ipv6
> 
> Hi,
> 
> I do have a system with systemd-networkd. IPv6AcceptRA is set to 1,
> which is not strictly needed, but I can easily dream up a use case
> where this is actually useful.
> 
> In the .network unit file, I have an IPv6 Gateway set statically:
> 
> [1/847]mh at milonga:~ $ cat /etc/systemd/network/milonga.network
> [Match]
> Name=e*
> 
> [Network]
> Gateway=2001:db8::1
> IPv6AcceptRA=yes
> DHCP=no
> 
> [Address]
> Address=2001:db8::43:100/64
> 
> When this system boots, it learns IPv6 default gateways from a HSRP
> pair of routers, resulting in this routing table:
> 
> 2001:67c:24f8:1002::/64 dev eth0 proto kernel metric 256  pref medium
> 2001:67c:24f8:1002::/64 dev eth0 proto ra metric 1024  pref medium
> fe80::/64 dev eth0 proto kernel metric 256  pref medium
> default metric 1024 
>         nexthop via 2001:67c:24f8:1002::1  dev eth0 weight 1
>         nexthop via fe80::21d:70ff:fe9f:65a0  dev eth0 weight 1
>         nexthop via fe80::21e:13ff:fe22:b510  dev eth0 weight 1
> 
> I am not sure whether it has any negative effects that the /64 route
> is entered twice.
> 
> The HSRP pair of routers has RA disabled. It will, however, answer
> router solicitations, a behavior which cannot be turned off on Cisco
> devices.
> 
> When the SLAAC learned IP address and routes expire, systemd-networkd
> removes the statically set default route as well, leaving the system
> without IPv6 connectivity outside the local network.
> 
> Expected behavior would be to leave the statically set route in place.
> 
> A workaround is setting IPv6AcceptRA=no, but this means that even after
> sending a router announcement, the system will not learn a new IP
> address. Sending out a router announcement is a frequently used trick to
> access a system whose network init has failed in some way and therefore
> the static IP address failed to show up.


Is this still an issue with 241-1 from unstable?
If so, it would be great if you can file a bug report upstream at
https://github.com/systemd/systemd/issues
Unfortunately I don't have a network setup where I could easily
reproduce the issue myself so it's better if you talk to upstream directly.

Regards,
Michael
-- 
Why is it that all of the instruments seeking intelligent life in the
universe are pointed away from Earth?

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