IPv6-only with SLAAC doesn't update resolv.conf

[Alexander Koeppe]

Hello list,

I'd like to make some experiences what would happen if tomorrow I'd wake
up in a IPv6-only world.

Therefore I've updated my /etc/network/interfaces file so to have only a
"iface wlan0 inet6 auto" statement w/o a "iface wlan0 inet dhcp" statement.

The observation I've made was that interface addressing works as
expected, but name resolution doesn't work, since /etc/resolv.conf still
points to the IPv4 address set by the DHCP config before.

I've also installed and started resolvconf package but this didn't help
either.
I've also read the Kernel IPv6 networking documentation (suspected a
/proc/sys/net flag) but found no variable that would influence this
behaviour.

What would be Linux' solution to such a typical setup where no DHCPv6
server is around, like in any consumer environment?

Is there a gap of thinking, either on my side or on Linux's developers side?

Regards
- Alex

[Jens Link]

Alexander Koeppe <form...@online.de> writes:

> Hello list,
>
> I'd like to make some experiences what would happen if tomorrow I'd wake
> up in a IPv6-only world.
>
> Therefore I've updated my /etc/network/interfaces file so to have only a
> "iface wlan0 inet6 auto" statement w/o a "iface wlan0 inet dhcp"
> statement.
>
> The observation I've made was that interface addressing works as
> expected, but name resolution doesn't work, since /etc/resolv.conf still
> points to the IPv4 address set by the DHCP config before.

So with out dhcpv6 client you can use "IPv6 Router Advertisement Options
for DNS Configuration" (RFC 5006^W6106^W8106)

To use this on Linux you need to install the rdnssd client. radvd also
supports this option if you are using Linux as router.

Note: This is not supported on several older model routers so you can
either change the router, use dual-stack or DHCPv6 (which wont work for
Android devices).

Jens
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[Alexander Koeppe]

Am 27.09.2018 um 21:02 schrieb Jens Link:
>
> So with out dhcpv6 client you can use "IPv6 Router Advertisement Options
> for DNS Configuration" (RFC 5006^W6106^W8106)
>

I've checked of course that the option is set in the router
advertisement in a packet capture.

Let me have a look at the rdnssd client.

Thanks
- Alex

P.S.
This box is just a netbook. Not running as a router.

[Pascal Hambourg]

Le 27/09/2018 à 20:49, Alexander Koeppe a écrit :
>
> I've also installed and started resolvconf package but this didn't help
> either.

Of course not. resolvconf does not create DNS, it just manages DNS
sources. It is useful if you have several DNS sources conflicting with
each other such as DHCP, SLAAC...

> What would be Linux' solution to such a typical setup where no DHCPv6
> server is around, like in any consumer environment?

Install rdnssd.

> Is there a gap of thinking, either on my side or on Linux's developers side?

The kernel alone receives IPv6 router advertisements (RAs) but will not
modify any file such as resolv.conf. So a userland process must do it.
This is the purpose of rdnssd.

[Alexander Koeppe]

Am 27.09.2018 um 23:14 schrieb Pascal Hambourg:
>
> The kernel alone receives IPv6 router advertisements (RAs) but will not
> modify any file such as resolv.conf. So a userland process must do it.
> This is the purpose of rdnssd.
>
>

Thanks for the explanation.

rdnssd works out perfectly which Jens Link had already suggested in a
previous message.

Thank you both.


- Alex

[Jens Link]

Alexander Koeppe <form...@online.de> writes:

> This box is just a netbook. Not running as a router.

But there are people using other things as Linux boxes as router. I
guess Cisco Cat 6500 or 4500 are still quite common and I know that they
wont support RFC5006/6106/8106 (at least in older versions of the
supervisor engine).