This is a nice tcpdump command line to see what you are getting from the switch as far as duplex and speed
tcpdump -nn -vvv -s 1500 -c 1 -i eth0 'ether[20:2] == 0x2000'
For linux the output should look like
tcpdump: listening on eth0, link-type EN10MB (Ethernet), capture size 1500 bytes
08:13:11.630525 snap 0:0:c:20:0 CDP v2, ttl: 180s, checksum: 692 (unverified)
Device-ID (0x01), length: 9 bytes: 'SWITCH1'
Version String (0x05), length: 190 bytes:
Cisco IOS Software, CBS30X0 Software (CBS30X0-LANBASE-M), Version 12.2(25)SEF1, RELEASE SOFTWARE (fc3)
Copyright (c) 1986-2006 by Cisco Systems, Inc.
Compiled Tue 23-May-06 15:26 by antonino
Platform (0x06), length: 20 bytes: 'cisco WS-CBS3020-HPQ'
Address (0x02), length: 13 bytes: IPv4 (1) 192.168.107.156
Port-ID (0x03), length: 18 bytes: 'GigabitEthernet0/8'
Capability (0x04), length: 4 bytes: (0x00000028): L2 Switch, IGMP snooping
Protocol-Hello option (0x08), length: 32 bytes:
VTP Management Domain (0x09), length: 10 bytes: 'esolutions'
Native VLAN ID (0x0a), length: 2 bytes: 155
Duplex (0x0b), length: 1 byte: full
AVVID trust bitmap (0x12), length: 1 byte: 0x00
AVVID untrusted ports CoS (0x13), length: 1 byte: 0x00
Management Addresses (0x16), length: 13 bytes: IPv4 (1) 192.168.107.156
1 packets captured
1 packets received by filter
0 packets dropped by kernel
