Got 2 switches connected together as follows port f0/26 on a cisco WS-C2950C-24 to port g0/48 on a cisco WS-C2960G-48TC-L They are auto sensing speed and duplex and I cannot find a command to tie them down. The problem is that SW1-NEWTON-FHH is auto sensing the duplex as full and SW1-MSU-FHH is auto sensing the duplex as half I have coppied the show ver, show int and the interface config from both switches. cisco WS-C2950C-24 show ver as follows:- Cisco Internetwork Operating System Software IOS (tm) C2950 Software (C2950-I6Q4L2-M), Version 12.1(22)EA7, RELEASE SOFTWARE (fc1) Copyright (c) 1986-2006 by cisco Systems, Inc. Compiled Fri 27-Jan-06 21:19 by antonino Image text-base: 0x80010000, data-base: 0x8056A000 ROM: Bootstrap program is C2950 boot loader SW1 uptime is 1 day, 23 hours, 27 minutes System returned to ROM by power-on System restarted at 08:02:32 BST Tue Mar 27 2007 System image file is "flash:c2950-i6q4l2-mz.121-22.EA7.bin" cisco WS-C2950C-24 (RC32300) processor (revision G0) with 21004K bytes of memory Processor board ID FOC0702Y00C Last reset from system-reset Running Enhanced Image 26 FastEthernet/IEEE 802.3 interface(s) 32K bytes of flash-simulated non-volatile configuration memory. Base ethernet MAC Address: 00:0B:FD:24:7B:80 Motherboard assembly number: 73-5750-11 Power supply part number: 34-0965-01 Motherboard serial number: FOC07010KE3 Power supply serial number: PHI06470GRU Model revision number: G0 Motherboard revision number: A0 Model number: WS-C2950C-24 System serial number: FOC0702Y00C Configuration register is 0xF cisco WS-C2950C-24 show int as follows:- FastEthernet0/26 is up, line protocol is up (connected) Hardware is Fast Ethernet, address is 000b.fd24.7b9a (bia 000b.fd24.7b9a) Description: Trunk Link to SW2 MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec, reliability 255/255, txload 1/255, rxload 1/255 Encapsulation ARPA, loopback not set Keepalive set (10 sec) Full-duplex, 100Mb/s, media type is 100BaseFX input flow-control is unsupported output flow-control is unsupported ARP type: ARPA, ARP Timeout 04:00:00 Last input 00:00:18, output 00:00:01, output hang never Last clearing of "show interface" counters never Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0 Queueing strategy: fifo Output queue: 0/40 (size/max) 5 minute input rate 0 bits/sec, 0 packets/sec 5 minute output rate 5000 bits/sec, 7 packets/sec 25884 packets input, 3824641 bytes, 0 no buffer Received 7991 broadcasts (0 multicast) 0 runts, 0 giants, 0 throttles 10 input errors, 10 CRC, 0 frame, 0 overrun, 0 ignored 0 watchdog, 7877 multicast, 0 pause input 0 input packets with dribble condition detected 922715 packets output, 97751463 bytes, 0 underruns 0 output errors, 0 collisions, 2 interface resets 0 babbles, 0 late collision, 0 deferred 0 lost carrier, 0 no carrier, 0 PAUSE output 0 output buffer failures, 0 output buffers swapped out cisco WS-C2950C-24 interface config as follows:- (This interface is an MTRJ 100BaseFX port) interface FastEthernet0/26 description Trunk Link to SW2 switchport trunk allowed vlan 111,999,1002-1005 switchport mode trunk storm-control broadcast level 0.20 storm-control action trap cisco WS-C2960G-48TC-L show ver as follows :- Cisco IOS Software, C2960 Software (C2960-LANBASE-M), Version 12.2(25)SEE2, RELE ASE SOFTWARE (fc1) Copyright (c) 1986-2006 by Cisco Systems, Inc. Compiled Fri 28-Jul-06 04:33 by yenanh Image text-base: 0x00003000, data-base: 0x00AA2F34 ROM: Bootstrap program is C2960 boot loader BOOTLDR: C2960 Boot Loader (C2960-HBOOT-M) Version 12.2(25r)SEE1, RELEASE SOFTWA RE (fc1) SW2 uptime is 1 day, 20 hours, 1 minute System returned to ROM by power-on System restarted at 11:34:12 BST Tue Mar 27 2007 System image file is "flash:c2960-lanbase-mz.122-25.SEE2/c2960-lanbase-mz.122-25 .SEE2.bin" cisco WS-C2960G-48TC-L (PowerPC405) processor (revision A0) with 61440K/4088K by tes of memory. Processor board ID FOC1051X5VU Last reset from power-on 2 Virtual Ethernet interfaces 48 Gigabit Ethernet interfaces The password-recovery mechanism is enabled. 64K bytes of flash-simulated non-volatile configuration memory. Base ethernet MAC Address : 00:1A:A2:31:02:80 Motherboard assembly number : 73-10300-06 Power supply part number : 341-0098-02 Motherboard serial number : FOC10511W56 Power supply serial number : AZS104902P4 Model revision number : A0 Motherboard revision number : B0 Model number : WS-C2960G-48TC-L System serial number : FOC1051X5VU Top Assembly Part Number : 800-27071-01 Top Assembly Revision Number : C0 Version ID : V01 CLEI Code Number : COM4A10BRA Hardware Board Revision Number : 0x01 Switch Ports Model SW Version SW Image ------ ----- ----- ---------- ---------- * 1 48 WS-C2960G-48TC-L 12.2(25)SEE2 C2960-LANBASE-M Configuration register is 0xF cisco WS-C2960G-48TC-L show int as follows :- GigabitEthernet0/48 is up, line protocol is up (connected) Hardware is Gigabit Ethernet, address is 001a.a231.02b0 (bia 001a.a231.02b0) Description: Trunk Link to SW1 MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec, reliability 255/255, txload 1/255, rxload 1/255 Encapsulation ARPA, loopback not set Keepalive not set Half-duplex, 100Mb/s, link type is auto, media type is 100BaseFX-FE SFP input flow-control is off, output flow-control is unsupported ARP type: ARPA, ARP Timeout 04:00:00 Last input 00:00:00, output 00:00:03, output hang never Last clearing of "show interface" counters never Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0 Queueing strategy: fifo Output queue: 0/40 (size/max) 5 minute input rate 7000 bits/sec, 9 packets/sec 5 minute output rate 0 bits/sec, 0 packets/sec 924700 packets input, 97956372 bytes, 0 no buffer Received 845874 broadcasts (0 multicast) 0 runts, 0 giants, 0 throttles 0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored 0 watchdog, 190293 multicast, 0 pause input 0 input packets with dribble condition detected 26274 packets output, 3858691 bytes, 0 underruns 0 output errors, 40 collisions, 1 interface resets 0 babbles, 12 late collision, 0 deferred 0 lost carrier, 0 no carrier, 0 PAUSE output 0 output buffer failures, 0 output buffers swapped out cisco WS-C2960G-48TC-L interface config as follows :- (This interface is a Small form Port 100BaseFX-FE SFP port) interface GigabitEthernet0/48 description Trunk Link to SW1 switchport trunk allowed vlan 111,999,1002-1005 switchport mode trunk storm-control broadcast level 0.20 storm-control action trap