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%CDP-4-DUPLEX_MISMATCH: duplex mismatch discovered on FastEthernet0/0 (not full duplex) between Router and switch

Sagar Patil
Cisco Employee
Cisco Employee

On Router

rAWKRdae01 uptime is 1 day, 23 hours, 47 minutes
System returned to ROM by power-on
System restarted at 06:13:17 GMT Wed Aug 13 2014
System image file is "flash:c2800nm-advipservicesk9-mz.124-15.T9.bin"

 

interface FastEthernet0/0
 no ip address
 duplex auto
 speed auto
end

 

Logs

================================

034146: Aug 15 05:55:40.231 UTC: %CDP-4-DUPLEX_MISMATCH: duplex mismatch discovered on FastEthernet0/0 (not full duplex), with sALKRdae01.baxter.com GigabitEthernet1/1/1 (full duplex).
034147: Aug 15 05:56:40.228 UTC: %CDP-4-DUPLEX_MISMATCH: duplex mismatch discovered on FastEthernet0/0 (not full duplex), with sALKRdae01.baxter.com GigabitEthernet1/1/1 (full duplex).
034148: Aug 15 05:57:04.420 UTC: %SEC-6-IPACCESSLOGP: list SecureInternet denied udp 192.230.123.37(53) -> 119.201.190.90(44014), 1 packet
034149: Aug 15 05:57:40.229 UTC: %CDP-4-DUPLEX_MISMATCH: duplex mismatch discovered on FastEthernet0/0 (not full duplex), with sALKRdae01.baxter.com GigabitEthernet1/1/1 (full duplex).
034150: Aug 15 05:58:40.230 UTC: %CDP-4-DUPLEX_MISMATCH: duplex mismatch discovered on FastEthernet0/0 (not full duplex), with sALKRdae01.baxter.com GigabitEthernet1/1/1 (full duplex).
034151: Aug 15 05:59:40.227 UTC: %CDP-4-DUPLEX_MISMATCH: duplex mismatch discovered on FastEthernet0/0 (not full duplex), with sALKRdae01.baxter.com GigabitEthernet1/1/1 (full duplex).
034152: Aug 15 06:00:05.707 UTC: %SEC-6-IPACCESSLOGP: list SecureInternet denied tcp 60.169.77.13(6000) -> 119.201.190.90(8088), 1 packet
034153: Aug 15 06:00:27.476 UTC: %SEC-6-IPACCESSLOGP: list SecureInternet denied tcp 109.120.169.206(80) -> 112.217.135.50(11), 1 packet
034154: Aug 15 06:00:40.224 UTC: %CDP-4-DUPLEX_MISMATCH: duplex mismatch discovered on FastEthernet0/0 (not full duplex), with sALKRdae01.baxter.com GigabitEthernet1/1/1 (full duplex).
034155: Aug 15 06:01:40.225 UTC: %CDP-4-DUPLEX_MISMATCH: duplex mismatch discovered on FastEthernet0/0 (not full duplex), with sALKRdae01.baxter.com GigabitEthernet1/1/1 (full duplex).

================================

 

On Switch

interface GigabitEthernet1/1/1
 description connection to rAWKRdae01
 switchport trunk native vlan 100
 switchport trunk allowed vlan 100
 switchport mode trunk
 load-interval 30
 speed 100
 duplex full
 service-policy output 3850_QUEUE_2P6Q3T
end

Log:

=================================

000440: Aug 15 05:44:59 GMT: %CDP-4-DUPLEX_MISMATCH: duplex mismatch discovered on GigabitEthernet1/1/1 (not half duplex), with rAWKRdae01.baxter.com FastEthernet0/0 (half duplex).
000441: Aug 15 05:45:59 GMT: %CDP-4-DUPLEX_MISMATCH: duplex mismatch discovered on GigabitEthernet1/1/1 (not half duplex), with rAWKRdae01.baxter.com FastEthernet0/0 (half duplex).
000442: Aug 15 05:46:59 GMT: %CDP-4-DUPLEX_MISMATCH: duplex mismatch discovered on GigabitEthernet1/1/1 (not half duplex), with rAWKRdae01.baxter.com FastEthernet0/0 (half duplex).
000443: Aug 15 05:47:59 GMT: %CDP-4-DUPLEX_MISMATCH: duplex mismatch discovered on GigabitEthernet1/1/1 (not half duplex), with rAWKRdae01.baxter.com FastEthernet0/0 (half duplex).
000444: Aug 15 05:48:22 GMT: %SNMP-3-AUTHFAIL: Authentication failure for SNMP req from host 10.5.35.33
000445: Aug 15 05:48:59 GMT: %CDP-4-DUPLEX_MISMATCH: duplex mismatch discovered on GigabitEthernet1/1/1 (not half duplex), with rAWKRdae01.baxter.com FastEthernet0/0 (half duplex).
000446: Aug 15 05:49:59 GMT: %CDP-4-DUPLEX_MISMATCH: duplex mismatch discovered on GigabitEthernet1/1/1 (not half duplex), with rAWKRdae01.baxter.com FastEthernet0/0 (half duplex).
000447: Aug 15 05:50:59 GMT: %CDP-4-DUPLEX_MISMATCH: duplex mismatch discovered on GigabitEthernet1/1/1 (not half duplex), with rAWKRdae01.baxter.com FastEthernet0/0 (half duplex).

==================================

 

I did try to change duplex setting on fa0/0 of router to Full, but the interface went down and I lost the connectivity to the switch.

 

8 Replies 8

I did try to change duplex setting on fa0/0 of router to Full, but the interface went down and I lost the connectivity to the switch.

 

Did you wait some time to let the divices reestablish the connection again?

I would configure the Switchport to auto/auto in that case. Autonegotiation works (most of the times ;-) ).

michael.wing
Level 1
Level 1

I'd personally try to configure both interfaces explicitly with Full Duplex and Speed 100. Gigabit uses 4 pairs for rx and tx wires in the cable Ethernet only uses 2 pairs, so being explicit on both ends should mean they both standardize to the same transmit and receive lines.

You'll also have to configure the router fa0/0 interface to trunk with the switch.

What kind of port are you configuring?

I've had instances like using SFP ports where you can't set speed or duplex.  If you use auto duplex you can't set full on the other side.

What model switch? The speed mismatch could be why the port is down

Thanasis_VIt
Level 1
Level 1

Hello,

 

I had this issue on a 2960x and an AIR2802.

try to set the port manually to full duplex and restart the connected device.

That solved the issue for me.

 

Thanasis

In the original post the router was configured to negotiate both speed and duplex. But the connected switch hard coded both speed and duplex. The router was attempting to negotiate duplex but the switch would not negotiate. When negotiation fails the router defaults to half duplex. So we should understand that when one device hard codes speed and/or duplex that the connected device also needs to hard code for duplex.

 

HTH

 

Rick 

HTH

Rick

Joseph W. Doherty
Hall of Fame
Hall of Fame

As Karsten notes, changing the duplex setting on the router may "blip" the interface, i.e. it may drop your remote session, but hopefully restart.

As Rick notes, if one side is auto and other side is hard coded full, the auto side should revert to half, which will cause duplex mismatch (in CDP) and horrible transfer performance.

More about that . . .

My understanding is that you really don't need to configure both sides' speed setting, as the side without being hard coded should be to determine it. However, if you hard code it on one side, I would recommend it be hard coded on the other side too.

Regarding duplex, if one side hard codes full, the other side must too. If one side hard codes half, the auto side should default to half. However, like speed, I would also recommend if duplex is being hard coded, it should be hard coded on both sides of the link.

Or more generally, both sides should be configured alike, regardless of whether differently configured speed/duplex settings will work correctly or not.

Lastly, unless you find it doesn't work, I would recommend auto/auto (as do hardware vendors [for copper Ethernet NICs at least made in this century - as Karsten also notes, auto works most of the time]). Besides avoiding the issues of where differently configured interfaces don't "play nicely", I understand auto often includes some additional analysis (e.g. link won't carry gig, ports should drop to FE) and may also provide auto-MDX/MDIX.

fhk
Level 1
Level 1

For example You can do like this
Edge-Router(config)#int e3/1
Edge-Router(config-if)#duplex  ?
full Force full duplex operation
half Force half-duplex operation

Edge-Router(config-if)#duplex half  ?

Edge-Router(config-if)#duplex half  hit on enter 

I think this will be help for anyone

 

 

"I think this will be help for anyone"

How so?  I.e. not sure what you're recommending.

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