IP forwarding with Nginx Proxy Manager (NPM)

[TheDreadPirate]

I tried to replicate your setup as close as possible and I can't get it to behave the same. When I typed in the bridge IP for Jellyfin in my browser, bypassing Nginx Proxy manager, it did report the bridge gateway as the client IP. But accessing Jellyfin through Nginx with my fake domain always reported my client's actual IP. I didn't even have to set a known proxy. I only have "proxy_buffering off" in the advanced tab.

The default docker bridge also doesn't have any options set.

The only thing that makes sense at this point is that Synology is doing something that I can't replicate.

Code:

[
    {
        "Name": "docker_default",
        "Id": "aa3e2d657cf1be32a31c2cab1718674d96718fc51792f1816c3789d8ca2c8b36",
        "Created": "2025-02-15T12:27:24.69189096-05:00",
        "Scope": "local",
        "Driver": "bridge",
        "EnableIPv6": false,
        "IPAM": {
            "Driver": "default",
            "Options": null,
            "Config": [
                {
                    "Subnet": "172.18.0.0/16",
                    "Gateway": "172.18.0.1"
                }
            ]
        },
        "Internal": false,
        "Attachable": false,
        "Ingress": false,
        "ConfigFrom": {
            "Network": ""
        },
        "ConfigOnly": false,
        "Containers": {
            "17e8baf3ef27984148e9ce3a34f8e050349672bb6bd8f6d02328d8e70ec818eb": {
                "Name": "nginx",
                "EndpointID": "7ff225f51b676445255ccc8f0534be4e99aba324be83c0fcad87c7c9fcb397bb",
                "MacAddress": "02:42:ac:12:00:03",
                "IPv4Address": "172.18.0.3/16",
                "IPv6Address": ""
            },
            "99d687774ec2de69cd913b745418fd984b0ab33b2181bbd76aca47c7f30b350c": {
                "Name": "jellyfin-testing",
                "EndpointID": "2bf23cc502963ac5473d03036c66ee3a78189ceff7c5363599c15ef85d915560",
                "MacAddress": "02:42:ac:12:00:02",
                "IPv4Address": "172.18.0.2/16",
                "IPv6Address": ""
            }
        },
        "Options": {},
        "Labels": {
            "com.docker.compose.network": "default",
            "com.docker.compose.project": "docker",
            "com.docker.compose.version": "2.28.1"
        }
    }
]