OmniSwitch OS6860/OS6900/OS10K Troubleshooting Guide Part No.032996-00 Rev.A
AOS Release 7.X and 8.X January 2015
Alcatel-Lucent Page 31 of 148
5.2. Advanced Troubleshooting Scenarios
MAC Addresses Not Aging Out
There are times when idle MAC addresses are not aging out of the MAC address table and it causes the MAC
address table size to increase.
Two common scenarios which cause the idle MAC addresses not to age out:
a). An interface on the switch is flapping (between every 1 to 4 minutes).
b). TCNs are received by the switch (between every 1 to 4 minutes) on one VLAN.
a). When port link status is toggled, due to spanning tree and other L2 protocol requirements, the switch needs
to flush the MAC addresses associated to that port in all VLANs. During this process to synchronize HW and
SW tables, the switch will block HW MAC table updates not being generated to SW. For this purpose, the port
level aging feature of the Broadcom ASIC is used.
When this port level aging register is modified (when port flushes are triggered), the global aging timer is
restarted.
Since the global aging timer is restarted, the MAC addresses on the other interfaces are not flushed causing the
MAC address table size to increase.
b). The same global aging timer behavior applies when TCNs are receive on a VLAN especially in per VLAN
STP mode.
When TCN is received on VLAN 10, the switch flushes all the MAC addresses in VLAN 10 and then reset the
global aging timer causing the idle MAC addresses of all other VLANs not to be flushed.
If there is a high-rate of TCNs on VLAN 10 to the switch (e.g. >once every 1 to 4 minutes) this will cause the
global aging timer (300 sec default) to keep resetting and idle MAC addresses of the other VLANs will not be
aged out from the switch.
Use the below steps to troubleshoot this issue on OS6860/OS6900/OS10K.
Scenario 1:
a). An interface in the switch is flapping (at least 1 time every 1 to 4 minutes).
Use the below “show interfaces” command to find out which port is showing the continous link flaps. Check
the below highlighted fields to understand which interface is recently flapping.
6860-> show interfaces 1/1/2
Chassis/Slot/Port 1/1/2 :
Operational Status : up,
Last Time Link Changed : Sat Feb 8 00:47:56 2014,
Number of Status Change: 9,
Type : Ethernet,
SFP/XFP : N/A,
EPP : Disabled,
Link-Quality : N/A,
MAC address : e8:e7:32:ab:1c:5f,
BandWidth (Megabits) : 1000, Duplex : Full,
Autonegotiation : 1 [ 1000-F 100-F 100-H 10-F 10-H ],
Long Frame Size(Bytes) : 9216,
Rx :
Bytes Received : 785209334, Unicast Frames : 255953,
Broadcast Frames: 8787093, M-cast Frames : 1420762,
UnderSize Frames: 0, OverSize Frames: 0,
Lost Frames : 0, Error Frames : 0,
CRC Error Frames: 0, Alignments Err : 0,
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