Think about your PC today.
How long does it take your PC to boot up? PCs today
don't take 30 seconds to boot up a lot of them are available within a few seconds or instantly.
That's a problem when we have technology such as spanning tree that take 30 seconds to converge and
forward traffic on a network what I'm gonna do is power cycle the devices
and I'll put the lab into simulation mode notice the switch is now booted up interfaces are showing
orange.
So what happens now is if the PC sends a renew message that DHCP message is gonna be sent to the
switch and then it's gonna be dropped until the ports go to green.
So once the ports go to green the DHCP request message can be forwarded but previously that message
from PC 1 was dropped because the ports were transitioning from listening to learning to forwarding.
So during that period of time DHCP messages will be dropped by the switch. So let's configure spanning
tree PortFast on the switch on which ports do I need to configure it.
I need to configure it on both the client ports and the server port.
We essentially want these three ports in this topology to transition to the forwarding state immediately.
Okay so here's the switch, what I'm gonna do is firstly give the switch a name and then I'm gonna
say interface range gigabit 101 23 those are the three ports in our network that have devices
connected to them.
So I'm gonna say spanning tree
and in this case we're going to select PortFast.
So PortFast, enter
notice we receive a warning message PortFast has been configured on this port.
You can introduce loops if you're not careful.
So use with caution but that's okay for this example.
So show run,
notice we've enabled PortFast on these three ports.
So what I'll do is save the switch configuration and what I'll do now is power cycle the devices
and what we should see is that as soon as the switch boots up the ports go to forwarding which they
have now and my PC can receive an IP address immediately.
So again if I do IP config slash renew the PC receives an IP address immediately the switch transitioned
immediately to the forwarding state on those three ports so spanning tree immediately transitioned to the
forwarding state on those ports.
Let's do that again just to prove the point he has the switch.
It's busy booting up and what you should notice is as soon as it boots up that the ports go green in
Packet Tracer.
There you go show spanning tree,
notice the ports are immediately forwarding and a PC such as PC 1 immediately receives an IP address
because the DHCP messages can be sent to the server immediately.
So there you go,
that's an example of spanning tree PortFast.
So what have you learnt? You've learnt that spanning tree PortFast transitions a Port directly
to the forwarding state instead of transitioning from listening to learning to forwarding with spanning
tree PortFast ports configured as spanning tree PortFast ports immediately transition to forwarding
which means that pieces can get IP addresses from DHB servers.
Users can log in to services such as domain controllers without any delay and the network works more
efficiently.
It's important that you understand what spanning tree PortFAst does for the CCNA exam.