ULA Address is not assigned in DHCPv6 client mode

cpalm · April 17, 2018, 4:35pm

Hello,
I have 2 LAN interfaces configured in LEDE 17.01.4.:
lan and lan6

lan is configured for a static IPv4 address and lan6 (@lan) is a DHCPv6 client.

In this configuration my main internet router assigns a DNSv6 server address which is an ULA-address. Unfortunately no interface got an ULA address assignment.

But if I configure an IPv6 assignment length of e.g. 64 to the lan interface (even with builtin IPv6 management disabled on that interface) an ULA-address is being assigned to that interface.

Is this the workaround to a bug that no ULA-address or route are being assigned to the lan6 interface?

Thanks for an explanation!

mikma · April 17, 2018, 9:26pm

Why isn't the DNSv6 server's ULA address reachable using the global IPv6 address as source address? If the route to the ULA address worked there should be no need to assign a ULA address to the LEDE device.

cpalm · April 18, 2018, 5:28am

Here is my (anonymized) IPv6 routing table:

Network	Target	Source	Metric	Table
lan	::/0	2003:b013:1305:9800:92f6:b1a0:beef:beef	640	main
lan	2003:b013:1305:9800::/56	2003:b013:1305:9800:92f6:b1a0:beef:beef	640	main
lan	2003:b013:1305:9800::/64		256	main
lan	fd23:4567::/64		1024	main
(eth0)	ff00::/8		256	local
DMZ	ff00::/8		256	local
lan	ff00::/8		256	local

When not configuring lan as mentioned it not only gets no IPv6 ULA address but the bold ULA-net routing entry is also missing which leads to the upstream router ULA-DNS address not being reachable (pingable).
Of course I could also configure a static IPv6 route but I think thats not how this is meant to be.
Or: Should the ULA-DNS be reachable through the default gateway? But why is it limited to this source address?

mikma · April 18, 2018, 7:04am

Have you got other global IPv6 addresses which can't use the default route?

cpalm · April 18, 2018, 9:54am

No. Or at least not yet. I'm planning to set up an OpenVPN Connection to another site.

lleachii · April 18, 2018, 10:16am

Why are you trying to route a LOCAL IPv6 addeess (the ULA)?

cpalm · April 18, 2018, 11:06am

Because the upstream router advertises it's DNS-service via it's ULA-address.

lleachii · April 18, 2018, 12:52pm

OK...emphasis on the word LOCAL...you shouldn't route ULAs, and if so (or even possible), it's surely against best practice. Also, that router would need a route back to you, if it's your ISP, that definitely won't work.

I would advise using the ULA of your router's DNS instance, since it's local to the other DNS server. You should ensure that you've added the entry in LAN Interface or the system DNS to make it work. Placing it in the WAN DNS entries will not work in this case since you only use LAN.