While going over the backward compatibility portion of RSTP, I noticed that it performs with the 802.1d timers if the RSTP switch is the root, but if the 802.1d switch is the root then the switch running 802.1w transitions to root/forwarding within a couple of seconds. Why the difference? I was under the impression that as soon as it labeled the link as P2p Peer(STP), then both sides of the link followed the 802.1d process, but this only happens if the switch running 802.1w is the root bridge.


_____________________________802.1D-SWITCH-IS-ROOT______________________________________________ _________

3750-3(config-if)#do sh span vlan 1

Spanning tree instance(s) for vlan 1 does not exist.

3750-3(config-if)#no shut
3750-3(config-if)#
Aug 29 17:51:36.198: setting bridge id (which=3) prio 4097 prio cfg 4096 sysid 1 (on) id 1001.0017.e01c.3280
Aug 29 17:51:36.206: RSTP(1): initializing port Fa1/0/9
Aug 29 17:51:36.206: STP SW: Fa1/0/9 new blocking req for 1 vlans
Aug 29 17:51:36.206: RSTP(1): Fa1/0/9 is now designated
Aug 29 17:51:36.215: RSTP(1): transmitting a proposal on Fa1/0/9RSTP(1):
Aug 29 17:51:36.215: FP R:1001.0017.e01c.3280 C:0 B:1001.0017.e01c.3280 P:800B A:0 T:14.2.F
3750-3(config-if)#
Aug 29 17:51:36.215: %LINK-3-UPDOWN: Interface FastEthernet1/0/9, changed state to up
Aug 29 17:51:37.213: RSTP(1): transmitting a proposal on Fa1/0/9RSTP(1):
Aug 29 17:51:37.213: FP R:1001.0017.e01c.3280 C:0 B:1001.0017.e01c.3280 P:800B A:0 T:14.2.F
3750-3(config-if)#
Aug 29 17:51:37.221: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet1/0/9, changed state to up
3750-3(config-if)#
Aug 29 17:51:38.144: RSTP(1): updt roles, received superior bpdu on Fa1/0/9
Aug 29 17:51:38.144: RSTP(1): Fa1/0/9
Aug 29 17:51:38.144: F:B R:1.ecc8.824f.6000 C:0 B:1.ecc8.824f.6000 P:8009 A:0 T:14.2.F
Aug 29 17:51:38.144: RSTP(1): Fa1/0/9 is now root port
Aug 29 17:51:38.144: STP SW: Fa1/0/9 new forwarding req for 1 vlans
Aug 29 17:51:38.144: STP[1]: Generating TC trap for port FastEthernet1/0/9
3750-3(config-if)#do sh span vlan 1

VLAN0001
Spanning tree enabled protocol rstp
Root ID Priority 1
Address ecc8.824f.6000
Cost 19
Port 11 (FastEthernet1/0/9)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 4097 (priority 4096 sys-id-ext 1)
Address 0017.e01c.3280
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300 sec

Interface Role Sts C
Aug 29 17:51:41.155: RSTP(1): Fa1/0/9 received a tc ackost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa1/0/9 Root FWD 19 128.11 P2p Peer(STP)


3750-3(config-if)#exit

3750-3(config)#spanning-tre vlan 1 priority 0
3750-3(config)#
Aug 29 17:52:21.270: setting bridge id (which=1) prio 1 prio cfg 0 sysid 1 (on) id 0001.0017.e01c.3280
Aug 29 17:52:21.270: RSTP(1): updt roles, non-tracked event
Aug 29 17:52:21.270: RSTP(1): we become the root bridge
Aug 29 17:52:21.270: RSTP(1): Fa1/0/9 is now designated
3750-3(config)#do sh span vlan 1

VLAN0001
Spanning tree enabled protocol rstp
Root ID Priority 1
Address 0017.e01c.3280
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 1 (priority 0 sys-id-ext 1)
Address 0017.e01c.3280
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300 sec

Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa1/0/9 Desg FWD 19 128.11 P2p Peer(STP)

_____________________________802.1W-SWITCH-IS-ROOT______________________________________________ __
3750-3(config)#
3750-3#
Aug 29 17:52:46.075: %SYS-5-CONFIG_I: Configured from console by console
3750-3#conf t
Enter configuration commands, one per line. End with CNTL/Z.
3750-3(config)#int fa1/0/9
3750-3(config-if)#shut
3750-3(config-if)#
Aug 29 17:53:44.669: %LINK-5-CHANGED: Interface FastEthernet1/0/9, changed state to administratively down
Aug 29 17:53:45.676: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet1/0/9, changed state to down
3750-3(config-if)#no shut
3750-3(config-if)#
Aug 29 17:53:52.588: setting bridge id (which=3) prio 1 prio cfg 0 sysid 1 (on) id 0001.0017.e01c.3280
Aug 29 17:53:52.597: RSTP(1): initializing port Fa1/0/9
Aug 29 17:53:52.597: STP SW: Fa1/0/9 new blocking req for 1 vlans
Aug 29 17:53:52.597: RSTP(1): Fa1/0/9 is now designated
Aug 29 17:53:52.605: RSTP(1): transmitting a proposal on Fa1/0/9RSTP(1):
Aug 29 17:53:52.605: FP R:1.0017.e01c.3280 C:0 B:1.0017.e01c.3280 P:800B A:0 T:14.2.F
Aug 29 17:53:52.932: %LINK-3-UPDOWN: Interface FastEthernet1
3750-3(config-if)#no shut/0/9, changed state to up
Aug 29 17:53:53.603: RSTP(1): transmitting a proposal on Fa1/0/9RSTP(1):
Aug 29 17:53:53.603: FP R:1.0017.e01c.3280 C:0 B:1.0017.e01c.3280 P:800B A:0 T:14.2.F
3750-3(config-if)#int fa1/0/9
Aug 29 17:53:53.939: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet1/0/9, changed state to up
3750-3(config-if)#int fa1/0/9
Aug 29 17:53:55.616: RSTP(1): transmitting a proposal on Fa1/0/9RSTP(1):
Aug 29 17:53:55.616: FP R:1.0017.e01c.3280 C:0 B:1.0017.e01c.3280 P:800B A:0 T:14.2.F
3750-3(config-if)#do sh span vlan 1

VLAN0001
Spanning tree enabled protocol rstp
Root ID Priority 1
Address 0017.e01c.3280
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 1 (priority 0 sys-id-ext 1)
Address 0017.e01c.3280
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300 sec

Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa1/0/9 Desg BLK 19 128.11 P2p Peer(STP)

3750-3(config-if)#
Aug 29 17:54:07.604: RSTP(1): Fa1/0/9 fdwhile Expired
Aug 29 17:54:07.604: STP SW: Fa1/0/9 new learning req for 1 vlans
3750-3(config-if)#
3750-3#
Aug 29 17:54:15.019: %SYS-5-CONFIG_I: Configured from console by console
3750-3#
Aug 29 17:54:22.611: RSTP(1): Fa1/0/9 fdwhile Expired
Aug 29 17:54:22.611: STP SW: Fa1/0/9 new forwarding req for 1 vlans