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New Member

STP Question

Should I be concerned with all of the designated ports showing up for this particular VLAN (the one that happens to have the most reported problems obtaining a dhcp address). Int Gi 1/1 is connected to our 4507 core switch and Gi 1/2 is connected to a 3550. All other interfaces are just endpoints (mostly thin clients).

CSC06INDWC170#sh spanning-tree vlan 210

VLAN0210

Spanning tree enabled protocol ieee

Root ID Priority 32978

Address 000c.85f5.6e80

Cost 4

Port 1 (GigabitEthernet1/1)

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32978 (priority 32768 sys-id-ext 210)

Address 0011.92d9.e480

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Aging Time 15

Interface Role Sts Cost Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Gi1/1 Root FWD 4 128.1 P2p

Gi1/2 Desg FWD 4 128.2 P2p

Fa2/3 Desg FWD 19 128.67 P2p

Fa2/5 Desg FWD 19 128.69 P2p

Fa2/11 Desg FWD 19 128.75 P2p

Fa2/14 Desg FWD 19 128.78 Shr

Fa2/15 Desg FWD 19 128.79 P2p

Fa2/16 Desg FWD 19 128.80 P2p

Interface Role Sts Cost Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Fa2/17 Desg FWD 19 128.81 P2p

Fa2/18 Desg FWD 19 128.82 P2p

Fa2/21 Desg FWD 19 128.85 P2p

Fa2/25 Desg FWD 19 128.89 P2p

Fa2/26 Desg FWD 19 128.90 P2p

Fa2/29 Desg FWD 19 128.93 P2p

Fa2/30 Desg FWD 19 128.94 P2p

Fa2/31 Desg FWD 19 128.95 P2p

Fa2/32 Desg FWD 19 128.96 P2p

Fa2/33 Desg FWD 19 128.97 P2p

Fa2/34 Desg FWD 19 128.98 P2p

Fa2/35 Desg FWD 19 128.99 Shr

Fa2/36 Desg FWD 19 128.100 P2p

Fa2/38 Desg FWD 19 128.102 P2p

Fa2/39 Desg FWD 19 128.103 P2p

Fa2/40 Desg FWD 19 128.104 P2p

Fa2/41 Desg FWD 19 128.105 P2p

Fa2/42 Desg FWD 19 128.106 P2p

Fa2/43 Desg FWD 19 128.107 P2p

Fa2/44 Desg FWD 19 128.108 P2p

Fa2/45 Desg FWD 19 128.109 P2p

Fa2/46 Desg FWD 19 128.110 P2p

Fa2/48 Desg FWD 19 128.112 P2p

Fa3/1 Desg FWD 19 128.129 P2p

Interface Role Sts Cost Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Fa3/2 Desg FWD 19 128.130 P2p

Fa3/3 Desg FWD 19 128.131 P2p

Fa3/4 Desg FWD 19 128.132 P2p

Fa3/5 Desg FWD 19 128.133 P2p

Fa3/6 Desg FWD 19 128.134 P2p

Fa3/7 Desg FWD 19 128.135 P2p

8 REPLIES

Re: STP Question

1. Are u running PVST

2. possible to get the diagram or description for the ports.

3. Address 000c.85f5.6e80 which switch has this mac-address.

Re: STP Question

You should not be concerned about the ports being designated. However, you should be concerned about those port not showing up as configured for portfast, specially if you have some DHCP problems.

Try configuring all the edge ports (ports connected to client) for portfast (spanning-tree portfast). On the latest IOS, you can do a global config (spanning-tree porfast default) that will configured automatically all your non trunking ports for portfast. Then, explicitly disable portfast on any link going to a bridge (spanning-tree portfast disable). That's your g1/1 and g1/2 probably.

Regards,

Francois

New Member

Re: STP Question

Attached is a diagram of the layout. The switches in the circle are the ones that have DHCP issues. The 3550/3560 have portfast enabled but also experience sporadic DHCP issues. We had 4 endpoints have issue today. Three were resolved by moving to a Foundry switch (before I knew the problem was happening) and the fourth I configured "spanning-tree bpdufilter enable" on the port and they were able to get a dhcp address immediately. That may have just been coincidence though.

Also...PVST is enabled on the switches.

Re: STP Question

BPDU filter should not help, portfast should. That's about all I can say. At layer 2, a switch does not have much influence on DHCP. By configuring portfast, you have your port going to forwarding immediately as soon as the link comes up. Without portfast, the port is blocked for 30 seconds before passing data traffic and may drop DHCP request of a fast client.

Other optimizations include disabling trunking and channeling negotiation. That was generally useful for some IPX clients, I don't think DHCP clients would benefits from the short added period of forwarding time it would provide. You can have a test though. But anyway, try portfast first. The output you forwarded list ports that: don't have portfast enabled -or- are receiving BPDUs (in which case, they are definitely not edge ports).

Regards,

Francois

New Member

Re: STP Question

Here is some output from show spanning-tree detail active. These do not have portfast enabled but why would there be BPDUs sent on this interface?

Port 78 (FastEthernet2/14) of VLAN0210 is forwarding

Port path cost 19, Port priority 128, Port Identifier 128.78.

Designated root has priority 32978, address 000c.85f5.6e80

Designated bridge has priority 32978, address 0011.92d9.e480

Designated port id is 128.78, designated path cost 4

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

Number of transitions to forwarding state: 1

Link type is shared by default

BPDU: sent 155082, received 0

Port 79 (FastEthernet2/15) of VLAN0210 is forwarding

Port path cost 19, Port priority 128, Port Identifier 128.79.

Designated root has priority 32978, address 000c.85f5.6e80

Designated bridge has priority 32978, address 0011.92d9.e480

Designated port id is 128.79, designated path cost 4

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

Number of transitions to forwarding state: 1

Link type is point-to-point by default

BPDU: sent 139129, received 0

Re: STP Question

With STP, the port that has the best information keeps advertising its presence. That's what happening here: there is no STP peer, so the port is "designated" and advertise its presence periodically (similar concept to a designated router, if you are rather a L3 guy;-)

BPDUs have no impact on DHCP. There's just going to be ignored by the L3 device that are connected to the port. Again, there is in fact very little that STP can do to mess up your DHCP client, except delaying the moment when the port is forwarding traffic. Years ago, when we had all those sensitive novell client, we would recommend to connect a hub between the server and the switch, to check if the connectivity issues were caused by portfast being too slow. You can try that out if you can identify a particular client that has consistent DHCP problem. There are other factor beside L2 that can cause your problems.

Regards,

Francois

New Member

Re: STP Question

Thank you. The more I've been looking into this the more questions I have. Some more "show spanning-tree detail active" :

VLAN0210 is executing the ieee compatible Spanning Tree protocol

Bridge Identifier has priority 32768, sysid 210, address 0011.92d9.e480

Configured hello time 2, max age 20, forward delay 15

Current root has priority 32978, address 000c.85f5.6e80

Root port is 1 (GigabitEthernet1/1), cost of root path is 4

Topology change flag not set, detected flag not set

Number of topology changes 49307 last change occurred 00:18:52 ago

from FastEthernet3/24

Times: hold 1, topology change 35, notification 2

hello 2, max age 20, forward delay 15

Timers: hello 0, topology change 0, notification 0, aging 300

Is the number of topology changes and the most recent one 18 minutes ago cause for concern? There hasn't been a switch plugged in or unplugged on this network in months.

New Member

Re: STP Question

Okay...more confusion. I just ran the same "show spanning-tree interface" command on the same switch and here is the output.

CSC06INDWC170#sh spanning-tree vlan 210

VLAN0210

Spanning tree enabled protocol ieee

Root ID Priority 32978

Address 000c.85f5.6e80

Cost 4

Port 1 (GigabitEthernet1/1)

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32978 (priority 32768 sys-id-ext 210)

Address 0011.92d9.e480

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Aging Time 300

Interface Role Sts Cost Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Gi1/1 Root FWD 4 128.1 P2p

Gi1/2 Desg FWD 4 128.2 P2p

Fa2/3 Desg FWD 19 128.67 Edge P2p

Fa2/5 Desg FWD 19 128.69 Edge P2p

Fa2/11 Desg FWD 19 128.75 Edge P2p

Fa2/14 Desg FWD 19 128.78 Edge Shr

Fa2/15 Desg FWD 19 128.79 Edge P2p

Fa2/16 Desg FWD 19 128.80 Edge P2p

Interface Role Sts Cost Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Fa2/17 Desg FWD 19 128.81 Edge P2p

Fa2/18 Desg FWD 19 128.82 Edge P2p

Fa2/21 Desg FWD 19 128.85 Edge P2p

Fa2/22 Desg FWD 19 128.86 Edge P2p

Fa2/25 Desg FWD 19 128.89 Edge P2p

Fa2/26 Desg FWD 19 128.90 Edge P2p

Fa2/29 Desg FWD 19 128.93 Edge P2p

Fa2/30 Desg FWD 19 128.94 Edge P2p

Fa2/31 Desg FWD 19 128.95 Edge P2p

Fa2/32 Desg FWD 19 128.96 Edge P2p

Fa2/33 Desg FWD 19 128.97 Edge P2p

Fa2/34 Desg FWD 19 128.98 Edge P2p

Fa2/35 Desg FWD 19 128.99 Edge Shr

Fa2/36 Desg FWD 19 128.100 Edge P2p

Fa2/38 Desg FWD 19 128.102 Edge P2p

Fa2/39 Desg FWD 19 128.103 Edge P2p

Fa2/40 Desg FWD 19 128.104 Edge P2p

Fa2/41 Desg FWD 19 128.105 Edge P2p

Fa2/42 Desg FWD 19 128.106 Edge P2p

Fa2/43 Desg FWD 19 128.107 Edge P2p

Fa2/44 Desg FWD 19 128.108 Edge P2p

Fa2/45 Desg FWD 19 128.109 Edge P2p

Fa2/46 Desg FWD 19 128.110 Edge P2p

Fa2/48 Desg FWD 19 128.112 Edge P2p

Why tonight would it be saying the ports are "Edge" and last night it did not say "Edge?"

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