Static Access Port vs. Portfast Command

Hey..

Can anyone please help me understand why setting ports to be access ports (switchport mode access) does not accomplish the same thing as Portfast?

I guess I am trying to understand why they are 2 separate commands. Wouldn't setting the port to be an Access port be good enough to tell the switch that loops cannot occur on those port since they are Access ports (therefore allowing those access ports to bypass the listening/learning states)?

Thank you.

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Comments

kalebksp

Just because a port is an access port does not mean that a switch will not be plugged in, it simply means that whatever is going to be plugged in will only be able to access the VLAN assigned to that port.

ColbyG

They are different things. An access port just means the port is not a trunk. PortFast is for devices that should come up quickly. Look into the "switchport host", this is somewhat in line with what you're talking about. It will make the port access and turn on PortFast.

down77

+1 for Colby. Setting the portfast command immediately transitions the port into STP forwarding mode.

One is for Spanning Tree (spanning-tree portfast), the other is for VLAN configuration (switchport mode access)... though the commands do compliment each other very nicely when used appropriately.

Regards

typesh

Thanks everyone. I understand now.

typesh

Hey I am running into the same problem distinguishing between switchport mode access and switchport nonegotiate.

To me they seem to accomplish the same thing. Can't really see what it is that I am missing....

Nonegotiate tells the port not to negotiate a trunk... but switchport mode access does the same thing.

kalebksp

switchport nonegotiate turns off DTP, which is Dynamic Trunking Protocol, the protocol that the switches use to negotiate a trunk. You can still use switchport mode trunk on both sides of the link to statically configure a trunk. However if you have one side set to dynamic and the other set statically with nonegotiate the dynamic switch will see it as an access port.

ColbyG

To add to what kaleb said.

Basically, typesh, you're right. If a port is configured as "access" it will not negoatiate a trunk. But if it's configured as access without the nonnegotiate command, then reconfigured as a trunk, it will still negotiate using DTP.

mella060

The nonegotiate command just stops DTP packets from being sent from an interface. By default both an access port and trunk port will send DTP packets.

Cucumber

typesh wrote: »

Hey..

Can anyone please help me understand why setting ports to be access ports (switchport mode access) does not accomplish the same thing as Portfast?

I guess I am trying to understand why they are 2 separate commands. Wouldn't setting the port to be an Access port be good enough to tell the switch that loops cannot occur on those port since they are Access ports (therefore allowing those access ports to bypass the listening/learning states)?

Thank you.

The confusion you are having stems from the fact that you think that access ports are meant for connecting end user devices like computers or printers.

Well, that is just wrong.

You can have a HUB or a Switch connected to an access port.

The same idea applies for Trunks. You can connect any type of device to a Trunk port as long as the NIC inserted into ssaid device can handle the trunking tagging/encapsulation of frames traversing the trunk.

In other words, you may have switches connected to Access ports and say, servers connected to Trunk ports.

Applying the Access or Trunk configuration on a port only instructs the switch to either handle one or many vlans on said port. It is not telling the switch the nature of devices you will connect to said port.

That is why PortFast comes as a separate command. Configuring Portfast on a port tells the switch that you are not connecting into said port, a device capable of creating a layer 2 loops on your network.

Contrary to what people believe, you can apply the PortFast command to a trunk port if such trunk is connected say, to a server. And you should not configure PortFast to an access port connected to a Hub.