Fastport with trunk port

[nnn_sss22]

Hello,

I heard in STP topology When we enable fastport on trunk port then loop can be create. 

My question is, How loop can be create? when we enable fastport then stp does not disable completely and still port can receive BPDUs then how loop can be created?

[paul driver]

Hello

Enabling Portfast on a access port means basically you are telling the switch not to expect stp bpdu's from this port so it safe to bypass the stp learning process and transision the port into a forwarding state straight away as this port has just an end host attached to it

The same happens a trunk port with trunk portfast, you are telling the switch that that trunk isnt going to receive any stp bpdus as it connecting to a device ( such a a multihomed server) so it safe to transition into a forwarding state straight away.

res
Paul

[nnn_sss22]

its mean. in trunk port, when we will enable portfast then this port can be bpdus but cant loop detect bcz STP functionalities are disable. right?

[paul driver · Accepted solution]

Hello

Correct if you enable this and you attach a device such as a switch to that port then you can create loops as by default the port will automatically transition to a forwarding state bypassing the stp process, it can be negate by enabling bgpuguard which will disable stp portfast and disable the port but this isnt on by default.

res

Paul