FritzBox chained to cable modem via Lan1: wrong IP assignments

[ramik]

I sent a FritzBox 7170 to a friend in the USA who needs a good voip solution, and we are having issues configuring it.

He has Cable Internet, with a cable model that provides 1 ethernet connection, he had before a normal wlan router (one with 1 WAN port, 4 lan, wlan).

When he connects the Fritz to the cable modem directly via LAN1, and having the Fritz set to act as a client (DHCP) on another network via LAN1, the internal PC connected to the fritz's port 2-3-4 will get the public IP of the cable modem (24.x.y.z), gateway will be the providers main gateway, same for DNS servers, and not an IP on the fritz network (192.168.178.x), and the fritz UI is not accessible, as if it is acting as a hub, without providing its webif for configuring things.

while if he connects his old router to the cable modem, and connects the Fritz via its LAN1 to the old router as a client, the fritz will act as expected: externally it has an IP on the other router local network (192.168.1.x), and internally provides computers and wlan an internal ip on the 192.168.178.x network (with the fritz as a gateway, and the fritz's DNS server), and this is without touching any configuration, the only difference is where the lan cable from LAN1 of the fritz is connected to: (1) directly cable modem or (2) another router.

Anybody know what is going on here?

 

[KunterBunter]

Sure. You have to setup the Fritzbox 7170 as a router (Internetverbindung selbst aufbauen (NAT-Router mit PPPoE oder IP)), and not as a client (Vorhandene Internetverbindung im Netzwerk mitbenutzen (IP-Client)), provided that the Fritzbox 7170 is capable of acting like this. Some (few) are restricted to not working as a router (see footnote).

 

[ramik]

Updated first post with screen shot of the current situation.

by client I mean that it takes its public address by dhcp (point (4) in screenshot), as the cable modem can return different IP's...

also, how is it that with these same configurations everything works when it is chained to the old router, and computers on ports lan2-3-4 gets fritz's ip's, while with the same exact config directly connected to cable modem it gets different addresses inside ?! with the current config the local lan should be always the same, regardless of what is behind the LAN1 port.

 

[KunterBunter]

The only thing possible is that the box is one of these with the hardware restriction in the switch module. Or the box has a hardware defect.
Did you try factory reset already? What is the serial number of the box?

 

[ramik]

what is this "hardware restriction in the switch module"?

this is an old fritz that I used to use as my main router with my ADSL for a couple of years, never had issues with it. also, the switch hardware is working just fine if it is connected to another lan

 

[KunterBunter]

Wonder why I asked for serial number of the box? The footnote (link above) writes:
*Bitte beachten Sie: Liegt die Seriennummer Ihrer FRITZ!Box Fon WLAN 7170
- in dem Bereich -Buchstabe-xxx.221.00.***.***
- oder zwischen -Buchstabe-xxx.228.00.000.001 und -Buchstabe-xxx.228.00.187.671
- oder zwischen -Buchstabe-xxx.229.00.000.001 und -Buchstabe-xxx.229.00.004.641
ist dieses Modell nicht Internet-via-LAN1-fähig.

 

[ramik]

oh, i missed the footnote...
Thanks for the info, I have to check the serial then, but when it is day in the US

 

[ramik]

Update:
Checked the serial, it is not in the interval of incompatible Fritzes (it's xxx.231.00.xxxx).

Also, the cable modem in use is a Motorola SB5120, nothing special about it, not even a web interface for management.

Update 2:
After several tries, restarts and updating of ip on PC and Fritz, the issue is fixed and the Fritz works as expected.