06-02-2004 03:37 PM - edited 03-02-2019 04:07 PM
Good afternoon friends. Can anyone point me to documentation on why it is a good idea, or not a good idea to statically set port speed and duplexing on interfaces connecting a router to a switch, a switch to a switch, or a switch to a PC/server. I've heard stories supporting both sides of this issue (some say statically set them, others say let auto negotiate determine it). I need best practice documentation. Not just what you've seen or what you've heard. Anything will be sufficient: white papers, TAC case notes, product release notes, anything. Thank you
06-02-2004 04:17 PM
In the past I have seen network problems related to port mismatches with port speed and duplex which will cause network errors, dropped packets and retransmissions. I am including a good document link.
LINKs:
Hope this helps,
Curt
06-04-2004 02:17 AM
for more reliable link and secure link state its recommended to statically set your port transfer mode to FULL/HALF and 10/100/1000 Mbps link speed .
attention to these notes :
-- A Port set to Full Duplex connected to another that set to half duplex should be checked for LATE COLLISION ERRORS.
-- A Port set to Half duplex connected to Full duplex port should be checked for FRAME CHECK SEQUENCE errors .
in this case you can use these CLI commands to set your port to work at your needs :
Switch>ena
Switch#conf t
Switch(config)#int fa 0/X
Switch(config-if)#sp 10 / 100 / au
Switch(config-if)#du ha / fu / au
Switch(config-if)# Ctrl+Z
in a router you can same command with little difference by your Router Series and IOS version .
Good Luck
Yours Truly
N.Baradaran
Senior Admin of Central Library - IUST university
06-07-2004 03:03 PM
On a big network it is next to impossible to hardcode everything , specially if you have people moving around all the time . Usually auto/auto works sufficently but there are still times when you have nic incompatibilities . If you have high priority servers and connections to other switches and routers those are the ones I would hardcode . If you a smaller network then maybe you could hardcode everything . When you are working on a network with 30000 nodes it's a little tough to hardcode everything . :-)
06-08-2004 06:10 AM
I agree with cgregg. Sometimes it doesn't negotiate properly when it's left at 'auto neg' as a result of this u end up getting quite a lot of errors & re-transmit.
I had a scenario where the link util was under 5% but the user was complaining about the slow performance and upon investigation found out that because of auto neg ON and mis-match duplex it was generating quite a bit of errors and the re-transmission rate was quite high as well.
As a norm on the server as well as the switch end, we normally leave the port speed as FIXED and auto neg FALSE to avoid the above scenario.
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