IPv6: UDM Pro behind OpenWrt

Hello guys,

I‘m looking for some help on my exotic setup. It is used in an command vehicle of the german red cross and thus needs to serve some special needs I dont want to go further into.

An OpenWRT router with an integrated LTE modem is used to provide internet while on the road. Because of the mentioned needs a Unifi Dream Machine Pro is used behind the OpenWRT router as the main router. The ISP only provides only IPv6 with an prefix length of 64. The internet connection on the OpenWRT works just fine but the UDM is not able to connect to the internet nor gets anything deligated by the OpenWRT router.

The UDM connects to the OpenWRT through an interface with a static protocol, prefix deligation length of 64, a dhcpv6 server with RA enabled and in server mode. On the same settings a normal client can connect to the internet without any issues. The WAN interface is configured to an IPv6 Internet connection with a prefix length of 64. On the network interface I configured the interface type to be „Prefix Delegation“ with RA turned on and on „high“. Range and DNS settings havent been changed.

I would be super happy if someone cloud helb me with this issue!

Just to understand the situation better:

  • you don't get any form of IPv4 connectivity from your mobile ISP (not even the usual NATed private IPv4 address)
  • you do get a single /64 from your ISP (is the modem/ WAN IP inside or outside of the prefix?)
  • as I understand this, you do need incoming connections over IPv6 for multiple devices behind the Unifi Dream Machine Pro

sounds like an assignment from hell, probably involving NAT64 - still, I'd run for the hills…

  • you don't get any form of IPv4 connectivity from your mobile ISP (not even the usual NATed private IPv4 address)

No, I only get a IPv6 adress

  • you do get a single /64 from your ISP (is the modem/ WAN IP inside or outside of the prefix?)

Yes, if the prefix is a:b:c:d::/64 the modem IP is a:b:c:d:e:f:g:h

  • as I understand this, you do need incoming connections over IPv6 for multiple devices behind the Unifi Dream Machine Pro

Correct, but I could live with a bridged OpenWRT router and the UDM connected directly to the WWAN interface.

ip6relay might do the trick.

actually it did the trick! My clients get an IPv6 address assigned and the UDM Pro can ping a wan address. A connection to the internet still doesnt work but I think thats an UDM problem.
I guess the OpenWrt side is solved. Thank you for your help!

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