Configure Debian to connect to ONT like IPoE/DHCP router provided by the ISP

My ISP provides a pre-configured Asus router running Linaro GCC 4.6-2012.02 which connects to ONT (fibre box) via Ethernet cable. I can SSH into the router and see the WAN interface:

18: vlan10@eth0:  mtu 1500 qdisc noqueue state UP qlen 1000
    link/ether fc:34:97:59:**:** brd ff:ff:ff:ff:ff:ff
    inet ***.***.176.118/30 brd ***.***.176.119 scope global vlan10
       valid_lft forever preferred_lft forever
    inet6 ****:****:2600:24d0::1/128 scope global 
       valid_lft forever preferred_lft forever
    inet6 ****::****:97ff:fe59:ee10/64 scope link 
       valid_lft forever preferred_lft forever

The goal is to configure a custom router running Debian 11 to do the same thing so that I could get rid of the ISP-provided router. The ISP provides some details how to configure custom routers: - Connection type: IPoE or DHCP - Internet IP Address: Get Dynamically from ISP - Domain Name Server (DNS): Get Automatically from ISP - VLAN Tagging (sometimes called IPTV settings): VID: 10 / PRIO: 0 - SIP ALG: Disabled - Connection Type: DHCP (with Prefix Delegation) - Domain Name Server (DNS): Get Automatically from ISP - Prefix length (or delegation size / ID): 56 - DHCPv6: Checked or ON The Debian box has already been configured to use VLAN. So, for this fibre WAN I tried:

auto eth0.10
iface eth0.10 inet6 dhcp
    accept_ra 2
    request_prefix 1

But it gets stuck in requesting DHCP info and never obtains an IP address from the ISP. How to approach this problem? The funny thing is that I have root SSH access to a Linux machine (the Asus router) which already does it, so I should by all means be able to translate its settings into Debian. But how?