dhcp IPv6 sets accept_ra to 0 and doesn't get IPv6 route

[Charles Peters II]

Configure IPv6 network so that the IP address is obtained through DHCPv6 and setup NetworkManager IPv6 to use the "Automatic (DHCP only)" method. accept_ra is then set to 0 and NetworkManager fails to obtain the IPv6 route.

Attached is a script /etc/NetworkManager/dispatcher.d/02allowIPv6route which works around the issue to set accept_ra to 1.

I am running Kubuntu 13.04, but I believe the bug is not limited to this release.

[Eric B (ebischoff)]

Same here.

I was wondering whether this is really a bug. Can't DHCPv6 advertise a default gateway like DHCP used to do for IPv4? It seems that it is out of scope for DHCPv6, and that you have to do it with RAs. So yes, it looks like a bug.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Eric B (ebischoff)]

As a side note: if you accept the RAs, you will not only get the missing routes, but also the SLAAC addresses. So this is not anymore the "Automatic (DHCP only)" option as advertised.

Maybe the bug report could be restated as
                  "Does the 'DHCP only' option for IPv6 in Network Manager make any sense?"
since you don't get routes with DHCPv6 alone, and without routes you cannot do much...

Apart from someone declaring the routes manually on the command line, I'm having a hard time to figure out a use case for this option. Perhaps someone has better scenarios to propose?

Tested with Ubuntu 13.10 Saucy Salamander.

[Mathieu Trudel-Lapierre (cyphermox)]

You can still get routes via DHCP, we just never request them; I think adding the static-routes option my help a lot in this regard. There are various options possible for DHCPv6... Would you be in a position to further describe your setup so we can add this to the test cases?

I'd be interested to know specifically, just to be sure, which pieces of information for the connection you expect to go through DHCPv6, and which ones you expect to be retrieved from the RA?

The DHCP only option is just that -- it bypasses RAs largely and just asks DHCP for as much information as it is possible. If you're using DHCP for just some pieces (like just the address) then you might want to make sure what the proper options are enabled in the RAs; such as OtherConfig and all (the bits that tell systems to further consult DHCP when they have received a RA).

[Eric B (ebischoff)]

Get routes via DHCPv6 ? Strange. The whole idea of disabling RAs in IPv6 is strange, anyway.

I don't expect anything from DHCPv6, I was just playing around with this option, trying to understand what it does.

I suppose that your questions apply to the original bug reporter. We'll let him answer, if he is still following this bug report.

Best,

[rm (rm)]

> As a side note: if you accept the RAs, you will not only get the missing routes, but also the SLAAC addresses. So this is not anymore the "Automatic (DHCP only)" option as advertised.

If this is not what you want, you should simply set

echo 1 > /proc/sys/net/ipv6/conf/ethX/accept_ra
echo 0 > /proc/sys/net/ipv6/conf/ethX/autoconf

But not disable accept_ra entirely.

> I think adding the static-routes option my help a lot in this regard.

No. The default route will come over RA in most real-world configurations. It is wrong to disable accept_ra with DHCPv6 only.

[Mathieu Trudel-Lapierre (cyphermox)]

Confirming. I had misunderstood the issue.

I can reproduce the problem here, so I'll work on a fix in NM code after discussing with the upstream developers.

Thanks!

[Eric B (ebischoff)]

Thanks to both of you for the more precise analysis of the problem and for your work on a patch to NM.

[Eloy Paris (peloy-chapus)]

Has this been discussed with upstream developers as mentioned in comment #8? This issue still exists in 0.9.8.8-0ubuntu28 (14.10). Don't know about newer NM versions.

[Alexander Kirsch (a.kirsch76)]

I ran into the same problem with 17.10 and I solved it without any fixed or workarounds. But this is not an ubuntu bug! It's a false configuration. There are 2 Options for automatic IPv6 configuration in network manager. "Automatic" and "Automatic (DHCP only)". IPv6 router advertisment is not part of dhcpv6 by spec! So I switch my config to "Automatic" which uses dhcpv6 and router advertisment. The kernel option /proc/sys/net/ipv6/conf/ethX/accept_ra is set to 1 (active) then! Problem solved!