what is the relevance of enable PORTFAST on a pc ?

[gman10]

Hi all,

We have a 2950 switch running Span Tree Protocol. Yesterday, 5 pc's in a lab lost their DHCP leased addresses and the only way to have them keep dynamic addresses was to enable portfast on these pc's.. wierd or what?

any clues?

thanks for all the can help and good evening.

gman

 

[computerhighguy]

Do you mean enabling spanning tree portfast on the switch inerface?

Portfast tells the device that they will not be particitaping in the spanning tree process. Basically, you are telling the device that whatever is connected to it will not have bridging loops. This is useful for workstations (like windows xp) in an active directory. If portfast is not enabled, then the workstations typically log on using cached information. This poses a problem with active directory managed software installation, active directory startup scripts and sometimes login scripts.

Are these cards Broadcom cards? We had some issues with some Dell Dimension (2300 series I think) with built in Broadcom cards not autonegotiating in a reasonable amount of time. We even tried to hard code some setting on the adapter, but no luck. Anyway.....

If you enabled portfast on an ethernet card (personally i have not seen this before), then it is bound by the same rules.


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[gman10]

Hi computerhighguy,

Yes they are Broadcom cards as a matter of fact! Thanks for your response and yes, I meant on the switch interface not the pc.. Autonegotiating principles were shot for a few pc's, the wait state before a script would fully log them in and so forth was time consuming. As soon as portfast was enabled on the switch interface (vlan for that group) it was fine.. funny coincidence that it was Broadcom but these cards are ubiquitous now eh?

gman

 

[vipergg]

Yes all user ports should have spanning tree portfast turned on , specially if you are running dhcp on your network otherwise it will timeout trying to pull an address from the server because it normally takes 45-50 seconds for spanning tree to runn thru it's cycle without portfast turned on .

 

[gman10]

hello all-

Can someone walk me thru how to enable portfast for "certain VLANS" on a switch?

thx

gman

 

[vipergg]

You don't enable portfast on a vlan basis , it is on port basis on the switch and you would have to tell us what model switch you have .

 

[gman10]

Hi vipergg,

In this scenario, I'm using 2950C switches.. so vlans are not the essentially what you would enable portfast to but infact a physical port basis alone.. ok, could you walk me thru it if you have a moment.

thanks for any help provided.

gman

 

[vipergg]

On each interface just issue the "switchport host" command . You can do multiple ports at once using the interface range command . Conf t , interface range f0/1 - 24 , enter.There is a space before and after the dash . This puts you into the interface range config mode , then just enter the "switchport host" comand , end , write mem .