At a very high level, I'm trying to connect a system that only supports DHCP on it's WAN interface to a PPPoE based Internet access and this has proven to be more complicated than expected.
The ISP we use requires PPPoE authentication for a GPON Internet Service. This is an easy setup on most router as I only need to create the relevant PPPoE session on the WAN interface and perform NAT and DHCP to LAN clients.
The problem I have is that for one specific deployment, I need to connect this Internet drop to equipment that doesn't support direct PPPoE, it only does DHCP on the WAN port. What I'm trying to do is implement a half-bridge in software (Linux or other) with 2 network interfaces. On the "Outside" port, it would perform the PPPoE authentication, take IP received, and offer it on the "Inside" port via DHCP so that this equipment can receive the public IP directly and then bridge (route) the Ethernet frames between the 2 ports.
Based on what I've seen, this is widely implemented in multiple DSL modems and called "PPP IP extension", "half-bridge" or "zero-ip bridge" but I can't find a reference on how to actually implement it under Linux or any non-ADSL modem.
The best I have right now is a 1-1 NAT implementation which somewhat works but still causes me issues because the equipment doesn't know it's correct WAN IP (it sees the private 1-1 NAT IP).
The whole solution is quite similar to https://serverfault.com/questions/840395/implementing-pppoe-half-bridge-ip-passthrough-to-suit-ipsec-vpn-firewall-applian but the public IP is dynamic and passed to the client via DHCP. Any pointer on where to start?
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