jutta hat geschrieben:soweit ich gesehen habe, hat der wrt320n kein modem eingebaut, sondern der wan-port ist ein 100 mbit/s ethernet-port. der wird also an einer telefonleitung nicht funktionieren. 
das bedeutet, dass du den router an ein dsl-modem anschliessen musst. dazu kannst du die fritzbox verwenden, wenn du entweder "pppoe-passthrough" aktivierst, oder die fritzbox als bridge ("nur modem") konfigurierst.
Hab das jetzt selbst nochmal auf der Cisco Website nachgelesen, ich kann das nicht eindeutig herauslesen, was für ein Port dieser gelbe nun ist. Die Konfigurationsmöglichkeiten deuten für mich jedoch schon auf Modem-Funktionalität hin:
Hier der Auszug aus dem Benutzerhandbuch:
Internet Setup
The Internet Setup section configures the Router to your 
Internet connection. Most of this information can be 
obtained through your ISP.
Internet Connection Type
Select the type of Internet connection your ISP provides 
from the drop-down menu. These are the available types:
• Automatic Configuration - DHCP
• Static IP
• PPPoE
• PPTP
• L2TP
• Telstra Cable
Automatic Configuration - DHCP
By default, the Router's Internet Connection Type is set 
to  Automatic Configuration - DHCP, which should be 
kept only if your ISP supports DHCP or you are connecting 
through a dynamic IP address. (This option usually applies 
to cable connections).
PPPoE
Some DSL-based ISPs use PPPoE (Point-to-Point Protocol 
over Ethernet) to establish Internet connections. If you are 
connected to the Internet through a DSL line, check with 
your ISP to see if they use PPPoE. If they do, you will have 
to enable PPPoE.
Internet Connection Type > PPPoE
Username and Password Enter the Username and 
Password provided by your ISP.
Service Name If provided by your ISP, enter the Service 
Name.
Connect on Demand: Max Idle Time You can configure 
the Router to cut the Internet connection after it has been 
inactive for a specified period of time (Max Idle Time). If 
your Internet connection has been terminated due to 
inactivity, Connect on Demand enables the Router to 
automatically re-establish your connection as soon as you 
attempt to access the Internet again. To use this option, 
select  Connect on Demand. In the  Max Idle Time field, 
enter the number of minutes you want to elapse before
your Internet connection terminates. The default Max Idle 
Time is 15 minutes.