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New Member

stp behaviour

Can somebody explain me this:

6509-1 (root)-------6509-2(backup)

| |

| |

| |

gi0/1 |

3560 gi0/2 -----------

fa0/10

|

|

1100

|

|

wireless station (ws)

I start ping prom ws to 6509-1 and to 3560

when I shutdown gi0/1 on 3560 ping does not interupt for 30 sec (2*forwarding delay)

Why? niether uplinkfast nor backbonefast are enabled

when I then do "no shut" on gi0/1 ping to 3560 interupts for 30 sec.

Why?

1 ACCEPTED SOLUTION

Accepted Solutions

Re: stp behaviour

Yes, edge ports need to be manually configured (spanning-tree portfast).

Your switch is doing a sync, meaning that it is temporarily reverting its non-edge designated port to discarding. On a network that is designed to optimize RSTP performance, the non-edge ports are connected to a neighbor switch running RSTP and the ports move quickly from discarding to forwarding. So if your port is not configured for portfast, it expect a switch on the other side to be able to go forwarding quickly after a sync. That's the price to pay for RSTP fast convergence (the edge port identification was also very important for STP anyway).

Configuring portfast on your edge port should then remove the delay at link up.

Regards,

Francois

4 REPLIES

Re: stp behaviour

Would the 3560 be running rapid-PVST or MST by any chance? If so, it would be able to switch over its root port quickly to gi0/2 when gi0/1 fails, even without uplinkfast.

As to the cam table update, you're probably lucky. Trying pinging from 6509-2 to the 3560 and you should see traffic disruption both ways.

regards,

Francois

New Member

Re: stp behaviour

You're right the switches run R-PVST. This replies the first question. And partially the second.

So I see traffic disruption from ws to 3560 because 3560 doesn't recognise fa0/10 as an EdgePort. Thus it waits for 30 sec in order to sync.

Do EdgePorts need manual configuration?

p.s. 1100 is not running STP

Re: stp behaviour

Yes, edge ports need to be manually configured (spanning-tree portfast).

Your switch is doing a sync, meaning that it is temporarily reverting its non-edge designated port to discarding. On a network that is designed to optimize RSTP performance, the non-edge ports are connected to a neighbor switch running RSTP and the ports move quickly from discarding to forwarding. So if your port is not configured for portfast, it expect a switch on the other side to be able to go forwarding quickly after a sync. That's the price to pay for RSTP fast convergence (the edge port identification was also very important for STP anyway).

Configuring portfast on your edge port should then remove the delay at link up.

Regards,

Francois

New Member

Re: stp behaviour

Hi,

what version of stp are u running?

could view verify your stp state diagram of ure network (using show spanning-tree on each of your four switches).

rgds

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