I am trying to replace an existing SOHO 91 with a SOHO 71. Neither router has configurable duplex or speed on interface Ethernet 0, which is the router's interface that connected to the router's built-in 4-port switch through the back plane. When a Cisco IP phone is plugged to the SOHO 91, and the IP phone is set to speed=auto, duplex=auto, SOHO 91's interface Ethernet0 shows 10/Full. When the same phone is plugged into the SOHO 71, Ethernet0 shows 10/half, and CDP is logging duplex mismatch messages. When I connect one of the SOHO 91's LAN ports to one of the SOHO 71's LAN ports (for configuration purposes -- I am accessing the site remotely), SOHO 91 is showing its interface Ethernet 0 as full duplex, but SOHO 71's Ethernet 0 interface is in half duplex. CDP is also logging the error with duplex mismatches.
SOHO 91's interface E0 (LAN ports) is not configurable for speed or duplex, and neither is SOHO 71's interface Ethernet0. So, something must be wrong with duplex negotiation between SOHO 71's interface Ethernet 0 and other (newer) Cisco devices (both SOHO 91 and Cisco 7941 IP phone). SOHO 91 has the option to configure duplex on its interface Ethernet1 (WAN interface), but SOHO 71 is missing this option on its interface Ethernet1 too. Incidentally, the duplex showing on its interface Ethernet 1 (connected to the DSL modem) is also half-duplex, which is not good. There's no option to set duplex on the DSL modem either.
I have searched the Internet and the Cisco web site, including TAC Case collection, all the documents on SOHO routers, and NetPro community, but I cannot find the answer to my question. Is it possible to set the SOHO 71 to correctly negotiate full duplex on both interfaces (E0 and E1). Also, does this router support full duplex?