Spantree Portfast

[kitt]

Hi- Being new to Cisco hubs & switches, I'm confused. We've run into a bottleneck somewhere which I've limited it to the 2nd floor. After looking at 3 of our switches' configurations, I've noticed that 1 out of the 3 does NOT have spantree portfast enabled on the ports. Could this be my bottleneck?<br>
THanks in advance,<br>
Kitt McNamee<br>

 

[ngreenfield]

It depends on what is connecting to your switch ports. You should have portfast enabled on those ports that are connected individual clients (or servers, depending on whether they have 1 or more NIC's on them). Portfast needs to be disabled (the default) if the port is connected to another internetworking device (switch, hub, router, etc.). It should not be a bottleneck. If you enable portfast, then you are disabling spanning tree on that port. Just remember that a switch is basically a multi-port bridge.<br>
<br>
Hope this helps.<br>
<br>
Neil Greenfield

 

[Brett]

There are several settings that can cause issues. You should have portfast enable as stated by Neil. In addition, trunking and etherchannel should be set off for clients. It would be helpful to know what type of switch you are using. If it is a Cat5K family, ensure that the supervisor is updated with the latest flash. If you are using 5225R's, there is a firmware update to address some of the connectivity issues. This means replacements from Cisco if the firmware/hardware rev is 2.0 or earlier. 2.1 and later appears to be ok. These things in combination on a Cat5K can cause what appear to be bottleneck issues.

 

[LHarvey]

I would like to agree with the existing posts. Expecially<br>with turning off trunking and channeling when you turn on <br>portfast.<br>However, I would like to make a slight correction. The<br>spantree protocol still runs on the port with portfast, the<br>port just starts forwarding imediatily while spantree goes<br>through the listening and learning modes. If spantree<br>detects a loop after finishing listening and learning, the<br>spantree protocol will still shut the port down, basicly<br>the portfast feature just allows you to (potentialy)'cause'<br>a temporary loop untill spantree catches on. Should be<br>under 30 seconds though. There is another command for<br>turning off spantree altogether (dont remember it off the<br>top of my head).<br><br>I have not had the portfast issue appear as a 'bottleneck'<br>in terms on bandwidth though. It usually manifests itself<br>in the form of clients not getting dhcp/bootp addresses and<br>the client assuming there is no network attachment due to<br>the time it takes the switch to start forwarding traffic.<br>The client usually gives up and may complain about no network<br>attachment when it continues to bootup without net login.<br><br>Leroy&nbsp;&nbsp;MCSE, MCNE, CCNA, CCDA<br>

 

[kitt]

Thanks for your posts. I resolved the problem. The hubs that are connected to these switches run at half duplex in autosense mode. The switch ports that these are connected to were set at full duplex @ 100mb. I switched those ports to autosense, and performance was great. Thanks again