Cisco Nexus 7000 does not keep MAC Address in MAC address table

[JoeNaRuTa]

Dear All,

I got some issue abot Cisco Nexus 7000 does not keep MAC Address in MAC address table.

I did check TCAM is not full.

When I show mac address-table count the number of dynamic MAC address are shudenly gone.

This N7K have 3 VDC, this issue to be found only 1 of 3 vdc

Ps. MAC aging time is 1800 for all VLAN.

Would you please help to answer my questions.

- Where can I verify to identicatify this issue ?

- What is/are posible root cuase ?

BRs

Joe.

[balaji.bandi]

what is the version of nexus code running

Look at the below troubleshoot guide :

https://www.cisco.com/c/en/us/support/docs/interfaces-modules/nexus-7000-f2-series-copper-1-10-gigabit-ethernet-module-enhanced/200399-Nexus-7000-F2-F2e-Understanding-and-mit.html

[JoeNaRuTa]

Hi BB

what is the version of nexus code running

- It running with oldest version , the vesion is 6.2(6)

[balaji.bandi]

thank you for the information check the guide if you can able to find anything ?

[JoeNaRuTa]

Hi BB

Thank you so much,

I’ll will check with your recommended and you know soon.

Be safe 

Joe

[Sergiu.Daniluk]

Hi @JoeNaRuTa 

The MAC address table is flushed in a specific vlan if there are STP topology changes received in that VLAN.

You can check this by using "show spanning tree vlan X detail" command.

If there are indeed topology changes, track down the source of it by following the receiving interface (info found in the same output).

Another thing which could prevent MAC learning is if there are a lot of MAC moves. This will trigger a MAC learning disabled state. 

To enable mac move notification you must configure the "logging level l2fm 5" on the switch, then check the "show logging log" for any syslog indicating mac moves.

Be safe,

Sergiu

[JoeNaRuTa]

Hi Sergiu

I appreciate the response,

To be cleared I have 4 Nexus devices, 2N7K and 2N5K

Both N7K run vpc and belong to same group.

Both N5K run vpc and belong to same group.

The connection between N7K and N5K is the VPC.

N7K1===N7K2

||             ||

N5K1===N5K2

N7K1 now is a root of all VLAN.

Both N7K are same issue "The MAC address table is flushed"

At N7K1 I found the source of TCN, They come from peer-link interface and sent from N7K2 tand belong to same VPC domain.

Then I track down to N7K2 and "show span detail" , I found output as below

======================================================================

VLAN0001 is executing the rstp compatible Spanning Tree protocol
Bridge Identifier has priority 32768, sysid 1, address 8478.ac21.6cc2
Configured hello time 2, max age 20, forward delay 15
Current root has priority 32769, address 0026.9819.a6c2
Root port is 4096 (port-channel1), cost of root path is 1
Topology change flag not set, detected flag not set
Number of topology changes 2 last change occurred 702:34:16 ago
from port-channel1
Times: hold 1, topology change 35, notification 2
hello 2, max age 20, forward delay 15
Timers: hello 0, topology change 0, notification 0

Port 4096 (port-channel1, vPC Peer-link) of VLAN0001 is root forwarding
Port path cost 1, Port priority 128, Port Identifier 128.4096
Designated root has priority 32769, address 0026.9819.a6c2
Designated bridge has priority 32769, address 0026.9819.a6c2
Designated port id is 128.4096, designated path cost 0
Timers: message age 2, forward delay 0, hold 0
Number of transitions to forwarding state: 1
The port type is network
Link type is point-to-point by default
BPDU: sent 1264662, received 1264641

Port 4105 (port-channel10, vPC) of VLAN0001 is designated forwarding
Port path cost 1, Port priority 128, Port Identifier 128.4105
Designated root has priority 32769, address 0026.9819.a6c2
Designated bridge has priority 32769, address 0026.9819.a6c2
Designated port id is 128.4105, designated path cost 0
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 0
Link type is point-to-point by default
BPDU: sent 0, received 0

=========================================================

As my understand the above output does not tell us about what is the source of TCN ... Am i right ?

Would you have any suggesttion ?

Thanks in Advanced.

Joe