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lyallp
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PostPosted: Sat Dec 15, 2012 12:38 am    Post subject: No support for DHCPv6 management Reply with quote

I have noticed recently a constantly repeating pair of messages in my system log.

Code:
Dec 15 10:59:50 lyalls-pc dhcpcd[2672]: eth1: Router Advertisement from fe80::43ff:fe6e:f107
Dec 15 10:59:50 lyalls-pc dhcpcd[2672]: eth1: no support for DHCPv6 management


My home router is a FritzBox 7390, which is fully IPv6 enabled.

I don't have any Cisco or other enterprise level networking equipment, which is what I imagine the 'management' is talking about.

So, I was wondering what I must do to make, at least, the no support message go away. Is it a kernel option I must tweak? If so what option?

Thanks, in advance :)
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gentoo_ram
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PostPosted: Sat Dec 15, 2012 7:07 pm    Post subject: Reply with quote

The message seems to be coming from dhcpcd. If your router doesn't do DHCPv6, then you don't need support in dhcpcd for ipv6 or you need to disable it. Your kernel will automatically configure itself if the router is sending IPv6 router advertisements. In other words, you don't need dhcpcd for IPv6.
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lyallp
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PostPosted: Sat Dec 15, 2012 10:26 pm    Post subject: Reply with quote

Yes, but I need dhcp for IPv4, which I still have.
At least, that's how I understand it.
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miket
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PostPosted: Mon Dec 17, 2012 5:07 am    Post subject: Reply with quote

lyallp wrote:
Yes, but I need dhcp for IPv4, which I still have.
At least, that's how I understand it.


Yes, if you're not using static IP addresses on your LAN, you need DHCP for IPv4. If all you want for IPv6 is stateless autoconfiguration, and you already have DHCPv4 in place to discover things like the nameserver address, there's no need for any client program (or daemon) to help you out: the IPv6 code in the kernel is supposed to respond to router advertisements and configure the interface automatically.

Stateful autoconfiguration is a different matter, and so is automatic discovery of IPv6 name servers or time servers: if you want those, you need DHCPv6.

From what you wrote, it seems your FritzBox router is sending those router adverisements and for some reason those are causing a disagreement between dhcpcd and the driver for the eth1 device.

I have to confess that the only machine I've got running with dhcpcd is at 5.2.12 (which is still in Portage), a version at which Roy Marples had not yet added IPv6 support. (For the most part, I use static IP addresses and no DHCP.) This means I can't talk from experience with the new version or even look at its documentation. It just leaves me these possibilites to suggest:

1. look to /etc/dhcpcd.conf to see if you can turn off DHCPv6 support, or at least find a way to disable stateful autoconfiguration. You still ought to be able to end up with the following: an IPv4 address (from DHCP), an IPv6 address (from stateless autoconfiguration), an IPv4 default route (from DCHP), an IPv6 default route (from stateless autoconfiguration), and an IPv4 nameserver address (which also returns AAAA records for IPv6).

2. go back to dhcpcd version 5.2.12 if the first suggestion doesn't work for you.

In the brave future world where your provider no longer assigns IPv4 addresses, we'll need to have figured out how to use DHCPv6. We're not there yet, though.
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lyallp
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PostPosted: Mon Dec 17, 2012 7:43 am    Post subject: Reply with quote

Thanks for taking the time to reply.

I am running net-misc/dhcpcd-5.6.4

I have all of my network connected devices, at home, running without fixed IP addresses defined within them. I do have some configured in the FritzBox DHCP settings to have 'fixed' IP addresses, but not many.

I am unsure as to the IPv6 readiness of some of the devices, such as a Wii, PS3, or a smart TV, but the PC's all run IPv6.

I will admit to being unsure what the warning actually means, whether it's something I need to pay attention to, but I prefer to not see repeated warnings if I can help it.
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miket
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PostPosted: Tue Dec 18, 2012 3:56 am    Post subject: Reply with quote

Well, time for a few more ideas. I'm with you on not wanting to see crazy warnings. First off, I'd imagine you're seeing those log entries in your /var/log/messages of a desktop machine, not, say, the router or one those network-facing appliances.

Do you see a public IPv6 adress on that machine? I'm assuming that it's eth1 you've got plugged into the router, so if you type ifconfig eth1, do you see a line like
Code:
inet6 addr: 2001:123:456:789:abc:def:123:456/64 Scope: Global


or, if you don't have the net-tools package (which is probably hard to do on Gentoo), enter this command and look for the same kind of IPv6 address
Code:
/sbin/ip addr show dev eth1


In any event, you should see an address that begins with 2, not f. If you have that, you should have IPv6 connectivity on that machine.


Next check for what dhcpcd may be trying to do for you. I got the newest SystemRescueCD, started it in a KVM instance with TAP networking so that it would route Layer 2 packets and let me get IPv6, and then I looked at the addresses I got. As a good Gentoo derivative SystemRescueCD uses dhcpcd. I never saw those screwy log message either. I looked at the man page for dhcpcd and found that that it tries to do IPv6 management only if autoconfiguration is turned off in the kernel. Enter this command to find out:
Code:
/sbin/sysctl -a | egrep 'net\.ipv6\.conf\..*\.autoconf'


This queries the autoconf settings for all your IPv6 devices (yes you can and *should* run the sysctl command as a normal user if you're querying). All or most of the settings should be set to 1. (If you want to read about the IPv6 configuration, take a look at the /usr/src/linux/Documentation/networking/ipv6.txt file on your machine.)

If, for some reason the values are 0, and you find that you don't have a public IPv6 address when you did the first step, this might be your problem. If autoconfiguration was turned off, I'd have to guess there was a reason someone did it because the kernel's default is to turn it on. To cure this, we go into the land of trickiness. As root, you would enter commands like this
Code:
sysctl net.ipv6.conf.all.autoconf=1


On the other hand, if autoconfiguration was already enabled, or if you did get a routable IPv6 address, you've got another problem. It would be at this point I would untar the dhcpcd tarball somewhere and grep for the error message. I've done that kind of thing quite a few times along the line; I've got a directory where I do such untarring.


If any of your other devices lack IPv6 support, they shouldn't even notice the router advertisements in the first place. They wouldn't be the cause of your mystery messages.

Let me know what you find out.
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lyallp
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PostPosted: Tue Dec 18, 2012 8:51 am    Post subject: Reply with quote

Wow, thanks for the reply.
To answer your questions.
My amd64 Gentoo desktop PC has a global IPv6 address, starting with 2, as you described.
All my kernel net.ipv6.conf.*.autoconf are set to 1.
I found the message in dhcpd, it's a warning.
Code:
   if (rap->flags & (ND_RA_FLAG_MANAGED | ND_RA_FLAG_OTHER)) {
      if (new_data)
         syslog(LOG_WARNING, "%s: no support for DHCPv6 management",
             ifp->name);


After digging around in my FritzBox I found the following setting
Code:
Additional IPv6 Routers in the Home Network
[ ] Allow IPv6 prefixes announced by other IPv6 routers in the home network
[X] Also announce DNSv6 server via router advertisement (RFC 5006)

Now I have to figure out if I need the DNSv6 being announced or not....
I suspect not given I only have 1 IPv6 router in my home.
I might try turning it off and see what happens. :)

Edit: nope, keeps happening :(
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UberLord
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PostPosted: Wed Dec 19, 2012 12:19 pm    Post subject: Reply with quote

Nothing to do with DNS in the RA (RFC 5006)

Basically it's because your router has set either the M or O flags.
M = IPv6 Addresses are available via DHCPv6
O = Other information is available via DHCPv6

dhcpcd-5.99.3 has the beginnings of DHCPv6 support, but earlier versions do not, but I felt it was appropriate to warn about this.
In summary, nothing to be worried about that much. To stop it from happening either disable IPv6 in dhcpcd.conf OR stop your router setting the M or O flag in the RA. Maybe an option to turn off the DHCPv6 server in the FritzBox but leave the DHCPv4 server intact?
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