"portfast" can connect with switch or not

Posted on 2014-11-25
Last Modified: 2014-11-27
hello Experts
below is the extract from Cisco web site, i am a little puzzled, the "portfast" port could or could not connected with a switch?

thank you

PortFast causes a switch or trunk port to enter the spanning tree forwarding state immediately, bypassing the listening and learning states.

You can use PortFast on switch or trunk ports that are connected to a single workstation, switch, or server to allow those devices to connect to the network immediately, instead of waiting for the port to transition from the listening and learning states to the forwarding state.

Caution  You can use PortFast to connect a single end station or a switch port to a switch port. If you enable PortFast on a port that is connected to another Layer 2 device, such as a switch, you might create network loops.
Question by:beardog1113
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Accepted Solution

Matt earned 200 total points
ID: 40463959
You should use "spanning-tree portfast" option only on ports with end-points connected (workstations, servers, printers). On ports where you have additional network device (hub,switch) do NOT use portfast.

Author Comment

ID: 40463963
You can use PortFast on switch or trunk ports that are connected to a single workstation, switch, or server to allow those devices to connect to the network immediately

for this sentence does it mean trunk mode port can be connect with switch?
or it is different meaning of this sentence?
or "switch" not meaning switch?

thank you

Assisted Solution

Matt earned 200 total points
ID: 40463973
To prevent loops from occuring in a network, the spanning tree PortFast mode should be configured only on nontrunking access ports because these ports typically do not transmit or receive BPDUs. The most secure implementation of PortFast is to enable it only on ports that connect end stations to switches.
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LVL 17

Assisted Solution

lruiz52 earned 100 total points
ID: 40464016
In agreement with Matt, switch means switch L2 device. Sentence gates you can enable portfast on an interface connected to another switch but you run the risk of creating a network loop.

Author Comment

ID: 40464031
if i have bpdu guard enabled, may i connect "portfast" port with a switch?

thank you
LVL 29

Assisted Solution

by:Predrag Jovic
Predrag Jovic earned 100 total points
ID: 40464248
if i have bpdu guard enabled, may i connect "portfast" port with a switch?
You can and it is safe to implement portfast that way.

Also, you can set porfast if you connect some third party unmanaged switch that has connected host devices, since those small switches don't send BPDU (STP is not present usually on those switches). BPDU guard with portfast is recommended also in that case, since if you create a loop in network with unmanaged switch switch will receive its own BPDU (or any other BPDU) and port will enter error-disabled state.

So, sure you can do that, but ... is it safe and for what purpose is better question?
LVL 50

Assisted Solution

by:Don Johnston
Don Johnston earned 100 total points
ID: 40464423
"can" means is possible.   As in: It is possible to configure portfast on an interface which will be connected to another switch.  Because it's possible doesn't make it a good idea.

Conversely, you can not connect an RJ-45 plug into an SFP socket.

Author Closing Comment

ID: 40468528
thank you all

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