Duplex Mismatch between Cisco 2960 (LANBase Image) and Cisco 6506 Switch

Unanswered Question
Jan 22nd, 2010


I have the following issue;

I am getting a duplex mismatch between a Cisco 2960 TT-L Switch running IOS 12.2(35) LAN Base Image (Gig0/1) and a Cisco 6506 Switch running IOS 12.2(33)SXH Adv IP Services (Gig2/19).

I have tried several combinations of the duplex/speed settings on both sides but the only that works is setting duplex/speed AUTO on the Cisco 2960 which ends up autonegotiating to HALF duplex and 100Mbps.

What cou;d be the issue? IOS bugs?



I have this problem too.
0 votes
  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 5 (1 ratings)
edwardwaithaka Fri, 01/22/2010 - 01:38


I have upgraded the Cisco 2960 Switch to version 12.2(52). The interfaces are now at FULL duplex but cannot negotiate to 1000Mbps.

zvondovec Fri, 01/22/2010 - 04:42


Can you put here results of sh run int ... commands?


edwardwaithaka Fri, 01/22/2010 - 04:57


Ports are on default;



int gig0/1

switchport mode access

switchport access vlan zzz

duplex auto

speed auto



int gig2/18

no switchport

ip address x.x.x.x y.y.y.y

no speed

no duplex

zvondovec Fri, 01/22/2010 - 05:36


Is there only cable between those 2 boxes, or is there some convertor (fiber optic)?

Also you can try speed nonegotiate command on both sides.


Leo Laohoo Fri, 01/22/2010 - 21:35

On both, try the following interface command "speed auto 1000".

glen.grant Sat, 01/23/2010 - 04:56

  It is generally advised you use auto on both sides for gigabit. If they are not negotiating gig then I would take a serious look at the cabling . Unlike fastether which takes 2 pairs you must have 8 good wires in the entire path between the 2 devices  in order to negotiate gig as gig uses all 8 wires to achieve gig speeds . Even 1 bad wire out of the 8  it will not negotiate gig .  Make sure speed negotation is actually turned on for the 6500. you can check this with the following counterintuitive  command   

no speed nonegotiate .  Verify with the command 
show interfaces GigabitEthernet slot/port transceiver properties
Good info for explaining the different states for gig port settings.  http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2SX/configuration/guide/intrface.html#wp1020621

jimenez.reuben Thu, 06/28/2012 - 15:20

On the 2960 switch the "dual purpose" uplinks need to be manually configured with "media-type" to be able to set speed/duplex. Default would not allow setting these 2 attributes.

interface GigabitEthernet0/1

switchport mode trunk

media-type rj45

speed 100

duplex full


GigabitEthernet0/1 is down, line protocol is down (notconnect)

Hardware is Gigabit Ethernet, address is

Description: Uplink to Cat01

MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec,

reliability 255/255, txload 1/255, rxload 1/255

Encapsulation ARPA, loopback not set

Keepalive not set

Full-duplex, 100Mb/s, link type is auto, media type is 10/100/1000BaseTX



This Discussion

Related Content