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Half duplex on 2612

Posted on 2004-10-17
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Last Modified: 2010-05-18
I have a 2612 router (10mb e0). During the sh run, I noticed it is in half duplex.
"interface Ethernet 0/0
ip address 192.168.1.50  255.255.255.0
half-duplex

 When I ran it at full duplex I suffered performance issues.  What would be the cause of the performance issues after running it full duplex. My clients are set to "auto." Perhaps I needed to reload their NIC because it still thinks the router is running at half?

ps: I thought 10mb e0s could only run at half???

Thanks
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Question by:dissolved
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NicBrey earned 150 total points
ID: 12335958
No, 10 mb/s can run full duplex.
Is the router interface connected to a switch?  Try hardcoding the switch port to 10/full. Auto does not work all that well. If it is connected to a hub, you can only run half duplex.
If you have a pc directly connected with a crossover cable, also try setting it to full on the PC.
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Author Comment

by:dissolved
ID: 12337982
THe setup is like this

Router (routing between VLANs)
  |
  |             <----------------Trunk Link (int FA0/24)
  |
Switch  (3 VLANs)
  |
  |
  |
Users

So I should hardcode port 24 on the switch to full duplex as well?  I'm assuming full duplex will yield better performance? (slightly faster?)
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by:lrmoore
lrmoore earned 175 total points
ID: 12338111
If you attempt to hard-code one end of any connection, then you must hardcode the other end device. You cannot hard code one and leave the other in autonegotiate. What happens is that when you manually set it, the autonegotiation is turned off. The default behavior of a (cisco) switchport is to default to half-duplex if no negotiation packet is received. So if you manually set the router interface to full duplex, the switchport now falls back to half-duplex and now you have a mismatch which causes error and severe performance issues.
 
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Author Comment

by:dissolved
ID: 12338664
So if I hardcode the router, I must hardcode the switch and the clients?  Or will the clients auto negotiate (windows clients with 3com nics)
Thanks
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Assisted Solution

by:Dr-IP
Dr-IP earned 175 total points
ID: 12338826
When it comes to interconnecting Cisco gear via Ethernet, I have found the best practice is not to use auto negotiation. At best it’s hit and miss, sometimes it negotiates, sometimes it doesn’t, and when it does, it rarely negotiates the optimal setting. So I always manually configure the link speed, and duplex on both ends.

As for full duplex 10M, some equipment can do it, but a lot can’t do it. So keep an eye on the error counters for a while after configuring it to make sure it is working properly, as I have on more than a few occasions been able configure full duplex 10M on both ends, yet it don’t work properly, and I had to revert back to half duplex. Also watch out when trying to do full duplex 10M to an unmanaged switch, as most of them simply refuse to run at full duplex when operating at 10M.    
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Author Comment

by:dissolved
ID: 12339250
Thanks! Got it working. Set the switchport and router e0 to both full duplex.
Should I set the clients to full, or let them auto negotiate?

Quick question though. I have a data drop from my switch (port 1) going to another room. This data drop feeds into a linksys hub. I have 4 pcs plugged into the hub. Is this going to effect whether or not these 4 pcs operate at full or half duplex or not? Or is this unrelated?
thanks!

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Expert Comment

by:lrmoore
ID: 12339302
Unrelated. Hubs only work at half-duplex anyway. If they connect to the hub, they are stuck at half. If it's really a switch, then you should keep the PCs at auto.
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by:dissolved
ID: 12342336
thanks everyone
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by:lrmoore
ID: 12342362
Anytime!

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