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#1 2020-10-03 09:41:00

proa_p
Member
Registered: 2016-04-16
Posts: 5

[ipv6] NetworkManager randomly auto-configures an address via SLAAC

Hello,

I am encountering a weird problem with my fresh arch installation. NetworkManager sometimes doesn't configure an ipv6 address other thant the link-local one. Rebooting the laptop or restarting the daemon sometimes solves the problem.
My home router has SLAAC set up and it works great with all the other devices including an old arch laptop with basically the same configuration and and and headless arch server using networkd. Well, the windows machines don't pick-up the correct DNSv6 servers but that is the expected behavior, go figure... smile

I don't have iptables or ip6tables active on my new laptop.
And the only configuration I added to NetworkManager.conf was to enable the privacy extentions:

[connection]
ipv6.ip6-privacy=2


Am i missing something? Can it be a weird driver bug because my machine is fairly recent (dell xps 13 9300)?

thanks for your input

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#2 2020-10-04 02:48:44

rsmarples
Member
Registered: 2009-05-12
Posts: 250

Re: [ipv6] NetworkManager randomly auto-configures an address via SLAAC

proa_p wrote:

Well, the windows machines don't pick-up the correct DNSv6 servers but that is the expected behavior, go figure... smile

Windows only accepts IPv6 DNS over DHCPv6.
Android only accepts IPv6 DNS over RA.

This sheer amount of dick waving has lead to system admins having to deploy both because both are popular!

Anyhow, a first port of call would be to try tcpdump or wireshark.
A conformant RA would be broadcast every 15 minutes.
If you *do* recieve a RA inside this time with prefixes with the A flag set then you know the RA broadcast is fine and you have a bug with your system.
Otherwise the router is at fault.

If it's a bug with your system, I recommend trying dhcpcd - but then I'm heavily biased as I'm the author smile

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#3 2020-10-04 13:04:01

proa_p
Member
Registered: 2016-04-16
Posts: 5

Re: [ipv6] NetworkManager randomly auto-configures an address via SLAAC

rsmarples wrote:
proa_p wrote:

Well, the windows machines don't pick-up the correct DNSv6 servers but that is the expected behavior, go figure... smile

Windows only accepts IPv6 DNS over DHCPv6.
Android only accepts IPv6 DNS over RA.

This sheer amount of dick waving has lead to system admins having to deploy both because both are popular!

Anyhow, a first port of call would be to try tcpdump or wireshark.
A conformant RA would be broadcast every 15 minutes.
If you *do* recieve a RA inside this time with prefixes with the A flag set then you know the RA broadcast is fine and you have a bug with your system.
Otherwise the router is at fault.

If it's a bug with your system, I recommend trying dhcpcd - but then I'm heavily biased as I'm the author smile


Thanks for your suggestion smile

So I did some wireshark captures on my laptop and also some tcpdump on my router.

I found that every-time the wireless interface goes up it sends a few Router Solicitations (to the ff02::2 address) as supposed to do. On the router side, I can see these packets and then the subsequent response with a Router Adverstisement to this address : ff02::1

But the weird thing is that sometimes my laptop doesn't receive the initial response RA packets and therefore the addresses aren't configured. Any idea why? Even if they are dropped at the kernel level I should still see them with wireshark, correct?

If I wait some time, as you said, the periodic RA packets will be received and the ipv6 addresses will be eventually be configured.

I will probably give dhcpd6 a try. At least I know who to contact if it keeps giving me trouble smile Congratulations! I admire people like you for writing pieces of software so important!

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#4 2020-10-04 19:53:00

rsmarples
Member
Registered: 2009-05-12
Posts: 250

Re: [ipv6] NetworkManager randomly auto-configures an address via SLAAC

proa_p wrote:

So I did some wireshark captures on my laptop and also some tcpdump on my router.

I found that every-time the wireless interface goes up it sends a few Router Solicitations (to the ff02::2 address) as supposed to do. On the router side, I can see these packets and then the subsequent response with a Router Adverstisement to this address : ff02::1

But the weird thing is that sometimes my laptop doesn't receive the initial response RA packets and therefore the addresses aren't configured. Any idea why? Even if they are dropped at the kernel level I should still see them with wireshark, correct?

Correct. From your description I would say any issue is with the Access Point.
I've had a few dodgey ones over the years with similar issues.
I now use a Ubiquiti AC-Pro AP and have never looked back.

I will probably give dhcpd6 a try. At least I know who to contact if it keeps giving me trouble smile Congratulations! I admire people like you for writing pieces of software so important!

Thanks smile

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