I'm running a network in a remote location comprised of some Mikrotik APs, wAP R ac with LTE cat 4 modem, and hAP ac^2 as the central switch and AP. I'm looking to replace the wAP R ac LTE with something else, probably Mikrotik LHGG. But I'm also looking for non-MT devices for the LTE modem/router functionality because there seems to be 5G available at the location and Mikrotik does not offer 5G devices with directional antennas, which I need due to distance to the single available BTS.

With the current wAP R ac LTE or if I go with LHGG there is no problem with routing - those devices have the LTE modem directly connected and provide me with RFC1918 IPv4 and with RFC 7278 IPv6. Those devices then perform DHCP for IPv6, RA for IPv6, routing, firewalling, NATing.

But how do I configure the network with a 3rd party LTE router? I can of course delegate the functions of addressing, firewalling and NATing to the device, but I am extremely happy with Mikrotik offering in this regard and I use additional features likew ireguard tunnels to other locations, which I'd like to keep running on the router of this network. So if I want to stick to those functions on a Mikrotik device, in this case my hAP ac^2 in the center of the network, I understand I'd need to configure the LTE router into passthrough mode, where it sends all traffic to a single MAC address (autodetected or manually enforced) of the hAP ac^2 router.

But how would the hAP ac^2 be then configured to properly receive this traffic and route it? Sadly there is no DHCPv6 with PD on mobile networks, so using DHCP and real IPv6 routing is out of question. I'd need the hAP ac^2 to perform a functionality similar to RFC 7278 for IPv6, and what would even be done for IPv4? Would it use DHCP to obtain the IP address from the mobile network?

Clearly Mikrotik OS is capable of operating like this when it has its own LTE interface. But how do I configure it to behave in this manner with another router connected over Ethernet? Also I need IPv6 for work, Legacy IP won't do.

Other brand devices may have a bridge mode which will allocate an IPv4 address via DHCP. Whether it'll work with IPv6 is down to their implementation.

I can answer my own question, but only partially. I have now a setup with a home network with a few Mikrotik devices serving as APs and one hAP ac³ serving as a router. As for the Internet access I'm testing 2 devices: Mikrotik LHG 18 and Zyxel NR7101. So far I have managed to make the setup work with Zyxel NR7101. The setup is the following:

Zyxel NR7101 is set up in bridge mode. As far as I understand it will send all IPv4 and IPv6 traffic to the 1st device contacting it. Mikrotik hAP ac³ has the following settigns:
- There is a bridge with Ethernet ports 2-5 and the WiFi interfaces. It is in the LAN interface group.
- Interface ether1 is outside of the bridge. It is in the WAN interface group.
- There is a standard stateful outbound-only firewall both for IPv4 and IPv6 on the device with masquerade on the WAN group for IPv4 traffic.
- IPv4 routing is handled by a DHCP client on ether1 and DHCP server on bridge and the aforementioned masquerade.

1. IPv6 settings: The router can't obtain IPv6 address on ether1 via SLAAC. Having it do it would create the same /64 network on the WAN and the LAN side of the router.

2. We still need the IPv6 prefix. For this we will use DHCPv6 with the following settings: This causes the Mikrotik router to obtain an IPv6 prefix from the LTE router and create a pool which can later be used to configure another interface. The Mikrotik router will install a single xxxx:xxxx:xxxx:xxxx::ffff/128 IPv6 address on ether1.

3. Configure IPv6 address on the bridge: The Mikrotik router will use the IPv6 prefix obtained from the LTE router to configure a /64 network on the bridge interface. I've created this configuration from the web gui, exporting it shows the address as ::zzzz:zzzz:zzzz:zzzz/64, where the z's are an EUI-64 address based on bridge's MAC address, even thought the eui-64 option is disabled.

4. Finally we can advertise the prefix and the router on the LAN side of the Mikrotik router. I've modified the "default" ND settings (Why is this called ND!? We're talking about RA here!) to cover *only* the bridge interface. The same configuration does not seem to work when using Mikrotik LHG 18 as a LTE router. Both Mikrotik LHG 18 and Zyxel NR7101 use Quectel modems, although different models. There is a dhcpv6 server running on Zyxel NR7101 (according to ps), so maybe there is none on the Quectel modem and I still need a DHCPv6 server on Mikrotik LHG 18. I will test this later.

This whole mess is due to mobile providers not offering IPv6 Prefix Delegation.

Hi, can you tell me, how you have configured Zyxel NR7101? I have paid fixed public IPv4 and IPv6/64 with the provider. NR7101 is set to IP passthrough (bridge mode). With IPv4 is not problem, going thru directly to my MKT. But I cannot obtain IPv6...

I don’t have the Zyxel router anymore, at that location I’ve decided to keep Mikrotik LHG LTE18 instead due to signal strength. But maybe I still can help. First thing to check is if the Zyxel router’s APN configuration set to request dual stack? Is the APN itself a type that will have the ISP provide dual stack? According to my previous post if those things work fine, you should be able to request an IPv6 prefix from Zyxel on Mikrotik using DHCP.