basic switch config - extra commands

[wavess]

Hi All

I'm refining my default switch config for cisco switches.  I came across these two commands.  Wondering if you use them for access switches, and why or why not.  Maybe you have some thoughts on this.

I have included a description of what I think each of them do.  I'm a beginner, so take this with a grain of salt - I may say something incorrectly.  Thanks.

spanning-tree mode rapid

-converges in 2 sec,  normal spanning tree takes 30-50 sec to converge.

- To get the benefit of rapid spanning tree, all the switches have to be running it, else if one is running it, that switch just reverts back to STP to be compatible with the other switches.

spanning-tree portfast default

-this command turns on portfast on all ports by default.  so now when the port comes online, like when you plug a device into it, it does not go into listening mode for 30 sec, but straight into forwarding mode.   

[David Ruess · Accepted solution]

Hello,

We absolutely use them on Access switches and sometimes distribution L2 switches (these are L2 functions).

spanning-tree mode rapid is the Rapid STP mechanism to prevent loops at Layer 2. It has faster convergence times than regular spanning tree. Its basically once you plug in an ethernet cable the amount of time it takes for the light to switch from amber to green (learning about traffic to forwarding traffic). As it says configure all your switches for this if you plan to use it. If not you will be using the default STP which is much slower.

Portfast default command enables portfast on all non-trunk interfaces (you can enable this command on individual ports with the 'spanning-tree portfast' command). In spanning tree it will take several seconds to start forwarding traffic on a port. Portfast bypasses this timer and puts the port right into forwarding traffic mode. This is for ports you KNOW do not have another switch/bridging device connected to and its just a computer/AP/printer/etc.

Hope that helps

-David

[Martin L]

I agree, Rapid should be default STP mode on all new switches; STP does take 30 sec (50 for re-converge)

in case of portfast default command, it is 2x15 seconds (learning and listening) not "listening mode for 30 sec"

Regards, ML
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[Joseph W. Doherty]

Well, last network job I had, having about 5,000 Enterprise network devices, both those commands were part of our standard configuration.