Question

How do I disable ULA addresses on my LAN interface? (I'm on a RUTX09 with RUTX_R_00.07.03.)

I already disabled the "built-in IPv6 management", but the ULA addresses are still there.

Under DHCP-Server > IPv6 Settings I have Router Advertisement-Service on Server mode and both DHCPv6-Service and NDP Proxy disabled. My client machines sucessfully receive RA messages with the global prefix from my mobile provider.

The additional ULA addresses cause problems ie with my DNS configuration: Along with the ULA prefix the RUTX advertises itself as a local DNS server. (My network has dedicated DNS servers with additional knowledge the RUTX does not have.) Client machines pick up the RUTX as an additional DNS server which leads to 50% of all inquiries being answered incorrectly.

Edit: I learned that the additionally announced prefix does not harm my network. Its just the rdnss option (25) part with the ula address of the RUTX which does. I changed the title of the question accordingly.

Answer 1

Hello,

  

Thank you for reaching out!

Perhaps the easiest solution here would be to advertise your DNS servers directly to the client machines. Configuration example on how this could be done can be found here.

The instructions would be as follows:

• Open SSH or CLI window;
• Run these commands with your own DNS servers instead of Google's:

uci -q delete dhcp.lan.dhcp_option
uci add_list dhcp.lan.dhcp_option="6,8.8.8.8,8.8.4.4"
uci commit dhcp
/etc/init.d/dnsmasq restart

uci -q delete dhcp.lan.dns
uci add_list dhcp.lan.dns="2001:4860:4860::8888"
uci add_list dhcp.lan.dns="2001:4860:4860::8844"
uci commit dhcp
/etc/init.d/odhcpd restart

• Disconnect and reconnect your clients. On Windows machines command ipconfig /renew can be run and DNS server can be checked by using the command ipconfig /all;
• Custom DNS servers should be handed to your devices:

 

More useful information regarding DNS and DHCP can be found in the same OpenWRT page.

  

Let me know if any more information is needed!

Best regards,
DaumantasG

Comments

Thanks for your fast reply.

I never used the RUTX as my DHCPv4 server, so I skipped the v4 part of your instructions. Although there is a odhcpd running on my RUTX, it does not pick up the dhcp.lan.dns configuration you suggested. After restarting the odhcpd I still can see the wrong RDNSS announcements.

root@router:~# tcpdump -vv -ni br-lan icmp6 and 'ip6[40] = 134'
[...]
   rdnss option (25), length 24 (3):  lifetime 1800s, addr: fd5b:2f4d:dfa1::1
     0x0000:  0000 0000 0708 fd5b 2f4d dfa1 0000 0000
     0x0010:  0000 0000 0001
[...]

I blindly tried dhcp.@dnsmasq[0].ra_dns='0' and dhcp.@dnsmasq[0].dns_service='0' with no luck.

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Could you also try the steps listed here (Disabling DNS role)? I've tried configuring this setup with a freshly reset device and only the specified addresses were assigned to Windows:

Also, that is correct, the first part of the configuration is IPv4-only and is not needed if only working with IPv6.

Best regards,
DaumantasG

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uci set dhcp.lan.dns_service="0"
uci set dhcp.lan.ra_dns="0"
uci commit dhcp
/etc/init.d/odhcpd restart

This did the trick. Thanks mate. :)

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Glad I could help!

  

Best regards,
DaumantasG