port erridisable state

Answered Question
Aug 2nd, 2008

hi everybody!

i find various reasons for a port to go into erridisable state such as pagp,late-collision,port securiy etc. But i did not find that port can go into errdisable state for duplex mismatch.

Rather the port stays up,showing excessive collision,runt etc.

am i correct? In cisco press book(bscmsn) by David Hucaby,various reasons are listed for the port to go into errdisable state.There is no duplex mismatch reason among them.

can a port go into errdisable state for duplex mismatch reason?

thanks a lot!

I have this problem too.
0 votes
Correct Answer by sundar.palaniappan about 8 years 4 months ago

Sure, duplex mismatch can cause the interface to go into an error disable state.

quoting from CCO:

""Duplex mismatch

Duplex mismatches are common because of failures to autonegotiate speed and duplex properly. Unlike a half duplex device, which must wait until there are no other devices that transmit on the same LAN segment, a full-duplex device transmits whenever the device has something to send, regardless of other devices. If this transmission occurs while the half-duplex device transmits, the half-duplex device considers this either a collision (during the slot time) or a late collision (after the slot time). Because the full-duplex side never expects collisions, this side never realizes that it must retransmit that dropped packet. A low percentage rate of collisions is normal with half duplex but is not normal with full duplex. A switch port that receives many late collisions usually indicates a duplex mismatch problem. Be sure that the ports on both sides of the cable are set to the same speed and duplex. The show interfaces interface_number command tells you the speed and duplex for Catalyst switch ports. Later versions of Cisco Discovery Protocol (CDP) can warn you about a duplex mismatch before the port is put in the error-disabled state.""

http://www.cisco.com/en/US/tech/tk389/tk621/technologies_tech_note09186a00806cd87b.shtml

HTH

Sundar

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Correct Answer
sundar.palaniappan Sat, 08/02/2008 - 13:46

Sure, duplex mismatch can cause the interface to go into an error disable state.

quoting from CCO:

""Duplex mismatch

Duplex mismatches are common because of failures to autonegotiate speed and duplex properly. Unlike a half duplex device, which must wait until there are no other devices that transmit on the same LAN segment, a full-duplex device transmits whenever the device has something to send, regardless of other devices. If this transmission occurs while the half-duplex device transmits, the half-duplex device considers this either a collision (during the slot time) or a late collision (after the slot time). Because the full-duplex side never expects collisions, this side never realizes that it must retransmit that dropped packet. A low percentage rate of collisions is normal with half duplex but is not normal with full duplex. A switch port that receives many late collisions usually indicates a duplex mismatch problem. Be sure that the ports on both sides of the cable are set to the same speed and duplex. The show interfaces interface_number command tells you the speed and duplex for Catalyst switch ports. Later versions of Cisco Discovery Protocol (CDP) can warn you about a duplex mismatch before the port is put in the error-disabled state.""

http://www.cisco.com/en/US/tech/tk389/tk621/technologies_tech_note09186a00806cd87b.shtml

HTH

Sundar

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