11-09-2004 06:52 AM - edited 03-02-2019 07:49 PM
Hi all,
Using the MAC notification feature on a Cisco 2950 I noticed that several MAC table address entries are cycling through delete and add operations:(sample)
History Index 26, Entry Timestamp 172524612, Despatch Timestamp 172524612
Operation: Added Vlan: 1 MAC Addr: 0000.c054.7eda Dot1dBasePort: 1
History Index 29, Entry Timestamp 172526813, Despatch Timestamp 172526813
Operation: Deleted Vlan: 1 MAC Addr: 0000.c054.7eda Dot1dBasePort: 1
History Index 30, Entry Timestamp 172527614, Despatch Timestamp 172527614
Operation: Added Vlan: 1 MAC Addr: 0000.c054.7eda Dot1dBasePort: 1
History Index 32, Entry Timestamp 172550818, Despatch Timestamp 172550818
Operation: Deleted Vlan: 1 MAC Addr: 0000.c054.7eda Dot1dBasePort: 1
History Index 33, Entry Timestamp 172551719, Despatch Timestamp 172551719
Operation: Added Vlan: 1 MAC Addr: 0000.c054.7eda Dot1dBasePort: 1
History Index 37, Entry Timestamp 172582435, Despatch Timestamp 172582435
Operation: Deleted Vlan: 1 MAC Addr: 0000.c054.7eda Dot1dBasePort: 1
History Index 39, Entry Timestamp 172584739, Despatch Timestamp 172584739
Operation: Added Vlan: 1 MAC Addr: 0000.c054.7eda Dot1dBasePort: 1
etc.
These adds and deletes are occuring about every 8-12 seconds. The MAC table entry aging timer is set to 300 seconds, the default. Any idea what is causing these MAC addresses to be added and deleted this way?
My FastEthernet ports are connected to NICs.
11-09-2004 07:05 AM
Do a "sh mac-address-table aging-time vlan 1" when this is happening and see if the MAC aging time is 15 seconds when the addresses are being deleted and relearnt. If it is, probably the switch is getting STP TCNs
http://www.cisco.com/warp/public/473/17.html
If you are getting TCNs, check to see if there is any link flaps. Make sure you have portfast enabled on user ports so that TCNs are not generated when a user reboots his workstation.
11-09-2004 07:34 AM
Thanks for your response. I cleared the mac address table then did the "sh mac-address-table aging-time vlan 1", but it always showed 300. Here is a look at the VLAN STP info.
sh spanning vlan 1
VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 4097
Address 0011.93b9.d900
Cost 3008
Port 25 (GigabitEthernet0/1)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 49153 (priority 49152 sys-id-ext 1)
Address 0011.bbb9.2ec0
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 15
Uplinkfast enabled
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/5 Desg FWD 3100 128.5 Shr
Fa0/6 Desg FWD 3100 128.6 Shr
Fa0/8 Desg FWD 3019 128.8 P2p
Fa0/10 Desg FWD 3019 128.10 P2p
Gi0/1 Root FWD 3004 128.25 P2p
Gi0/2 Altn BLK 3004 128.26 P2p
Portfast is not enabled.
Seems as though something is causing my mac addresses to be deleted before they age out, then readds them. Any idea what would cause this? Any thing else I can show that would help?
Thanks for the help.
11-09-2004 07:39 AM
Issue "sh spanning-tree vlan 1 detail" on the STP root switch and post the first few lines. Looks like your root switch is on Gig0/1
Here is an example
2950#sh spanning-tree vlan 1 detail
VLAN0001 is executing the ieee compatible Spanning Tree protocol
Bridge Identifier has priority 32768, sysid 1, address 0005.7428.1c40
Configured hello time 2, max age 20, forward delay 15
We are the root of the spanning tree
Topology change flag not set, detected flag not set
Number of topology changes 7 last change occurred 22:43:35 ago <<<<-------
from FastEthernet0/1
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
11-09-2004 07:57 AM
sh spanning-tree det
VLAN0001 is executing the ieee compatible Spanning Tree protocol
Bridge Identifier has priority 49152, sysid 1, address 0011.bbb9.2ec0
Configured hello time 2, max age 20, forward delay 15
Current root has priority 4097, address 0011.93b9.d900
Root port is 25 (GigabitEthernet0/1), cost of root path is 3008
Topology change flag not set, detected flag not set
Number of topology changes 236 last change occurred 01:12:42 ago
from FastEthernet0/1
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
Uplinkfast enabled
Port 5 (FastEthernet0/5) of VLAN0001 is forwarding
Port path cost 3100, Port priority 128, Port Identifier 128.5.
Designated root has priority 4097, address 0011.93b9.d900
Designated bridge has priority 49153, address 0011.bbb9.2ec0
Designated port id is 128.5, designated path cost 3008
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 1
Link type is shared by default
BPDU: sent 18226, received 0
Port 6 (FastEthernet0/6) of VLAN0001 is forwarding
Port path cost 3100, Port priority 128, Port Identifier 128.6.
Designated root has priority 4097, address 0011.93b9.d900
Designated bridge has priority 49153, address 0011.bbb9.2ec0
Designated port id is 128.6, designated path cost 3008
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 1
Link type is shared by default
BPDU: sent 18224, received 0
Port 8 (FastEthernet0/8) of VLAN0001 is forwarding
Port path cost 3019, Port priority 128, Port Identifier 128.8.
Designated root has priority 4097, address 0011.93b9.d900
Designated bridge has priority 49153, address 0011.bbb9.2ec0
Designated port id is 128.8, designated path cost 3008
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 3724, received 0
Port 10 (FastEthernet0/10) of VLAN0001 is forwarding
Port path cost 3019, Port priority 128, Port Identifier 128.10.
Designated root has priority 4097, address 0011.93b9.d900
Designated bridge has priority 49153, address 0011.bbb9.2ec0
Designated port id is 128.10, designated path cost 3008
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 173777, received 0
Port 25 (GigabitEthernet0/1) of VLAN0001 is forwarding
Port path cost 3004, Port priority 128, Port Identifier 128.25.
Designated root has priority 4097, address 0011.93b9.d900
Designated bridge has priority 32769, address 0011.bb3d.4f00
Designated port id is 128.8, designated path cost 4
Timers: message age 3, forward delay 0, hold 0
Number of transitions to forwarding state: 1
Link type is point-to-point by default
BPDU: sent 215, received 726863
Port 26 (GigabitEthernet0/2) of VLAN0001 is blocking
Port path cost 3004, Port priority 128, Port Identifier 128.26.
Designated root has priority 4097, address 0011.93b9.d900
Designated bridge has priority 16385, address 0011.93b9.e200
Designated port id is 128.3, designated path cost 12
Timers: message age 5, forward delay 0, hold 0
Number of transitions to forwarding state: 0
Link type is point-to-point by default
BPDU: sent 2, received 727415
Discover and save your favorite ideas. Come back to expert answers, step-by-step guides, recent topics, and more.
New here? Get started with these tips. How to use Community New member guide