Rapid PVST and "Edge Shr" state

[gnijs]

Hi all,

I have a port that is in "Edge Shr" state. I understand this is becuase it is running in half duplex mode.

This is because an (old!) device is connected with half-duplex NIC only.

The question now is:

* when there is a Topology Change (TCN), will this port be affected ? ie. will there be a rapid transition or not ?

According to the doc:

"RSTP can only achieve rapid transition to the forwarding state on edge       ports and on point-to-point links"

But does this mean that the port needs to be AND edge AND P2P ? Or is one condition enough ?

Note: that my port is an EDGE port, but not a P2P port ?

Do i gain something by configuring this port in P2P mode ?

regards,

Geert

The complete config of the port:

spanning-tree portfast bpdufilter default

interface FastEthernet1/0/2

power inline never

switchport access vlan xxxxx

switchport mode access

switchport port-security violation restrict

no snmp trap link-status

no mdix auto

storm-control broadcast level 5.00 3.00

storm-control action shutdown

storm-control action trap

spanning-tree portfast

spanning-tree bpduguard enable

end

#sh spanning-tree int fa1/0/2 detail

Port 4 (FastEthernet1/0/2) of VLAN0003 is designated forwarding

   Port path cost 100, Port priority 128, Port Identifier 128.4.

   Designated root has priority 8195, address 001a.3028.eac0

   Designated bridge has priority 32771, address 001b.90b7.fd80

   Designated port id is 128.4, designated path cost 4

   Timers: message age 0, forward delay 0, hold 0

   Number of transitions to forwarding state: 7

   The port is in the portfast mode

  Link type is shared by default

   Bpdu guard is enabled

   Bpdu filter is enabled by default

   BPDU: sent 11, received 0

[Peter Paluch · Accepted solution]

Hello Geert,

If shared ports are both shared and non-edge, there will be no rapid transition. RSTP does not use the Proposal/Agreement mechanism on shared links, and will fall back to timers.

If a shared port is configured as an edge port (and is really connected to an end device), it will be rapidly put into Forwarding state as soon as it is connected, it will not generate TC events and will not be influenced by topology changes inside the network.

The RSTP is capable of rapid convergence on either point-to-point links or on edge ports.

Please feel welcome to ask further!

Best regards,

Peter

[Mohamed Sobair · Accepted solution]

Hi,

Just adding to Peter's Post, a rapid convergence occurs on either Point to point rstp link types and if the port is Edge port.

I will always set manually (Spanning-tree link-type point-to-point) on ports running on half duplex mode as a best practise, although its not required in Edge ports, but some times you may have ports that are not Edge ports , so you need to have this command applied on the ports running on half duplex mode to achieve RSTP rapid convergence.

Regards,

Mohamed