MAC address not retained in table for timeout duration

[cghareeb]

Greetings,

I have a Catalyst 6509 running IOS 12.1(19)E1. The Catalyst 6509 has a 2950-12 (IOS 12.1(12c)EA1) connected on port Gi3/2 at the 2950's Gi0/1.

The 2950's Vlan1 interface MAC address appears from time to time in the 6509's MAC address table, however, when it does, it does not appear to stay in the table for the 300 second aging time.

The MAC address also does not appear to be reporting when queried by the "sh mac int" and the "sh mac vlan" commands. Note the following session log...the duration between the first and last command being issued is only 30 seconds:

Cat6509#sh mac int gi3/2 | inc 000c.8509

* 1 000c.8509.170d dynamic Yes -- Gi3/2

Cat6509#sh mac vlan 1 | inc 000c.8509

Cat6509#sh mac int gi3/2 | inc 000c.8509

* 1 000c.8509.170d dynamic Yes -- Gi3/2

* 133 000c.8509.1700 dynamic Yes -- Gi3/2

Cat6509#sh mac vlan 1 | inc 000c.8509

Cat6509#sh mac int gi3/2 | inc 000c.8509

* 1 000c.8509.170d dynamic Yes -- Gi3/2

* 133 000c.8509.1700 dynamic Yes -- Gi3/2

Cat6509#sh mac vlan 1 | inc 000c.8509

Cat6509#sh mac vlan 1

Codes: * - primary entry

vlan mac address type learn qos ports

------+----------------+--------+-----+---+--------------------------

* 1 0100.5e01.012a static Yes -- Gi2/2

* 1 0100.5e01.0129 static Yes -- Gi2/2

* 1 0100.5e01.0120 static Yes -- Gi2/2

* 1 000c.cfad.d400 static No -- Router

* 1 0100.5e01.0133 static Yes -- Gi2/2

* 1 0100.5e02.8586 static Yes -- Gi2/2

* 1 0100.5e01.0134 static Yes -- Gi2/2

* 1 0100.5e01.010b static Yes -- Gi2/2

* 1 0100.5e01.010c static Yes -- Gi2/2

* 1 0100.5e7f.fffd static Yes --

* 1 0100.5e01.011f static Yes -- Gi2/2

* 1 0100.5e01.0115 static Yes -- Gi2/2

* 1 0100.5e01.0116 static Yes -- Gi2/2

Cat6509#sh mac int gi3/2 | inc 000c.8509

* 1 000c.8509.170d dynamic Yes -- Gi3/2

* 3 000c.8509.170d dynamic Yes -- Gi3/2

Cat6509#sh mac ag

Vlan Aging Time

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

Global 300

no vlan age other than global age configured

Cat6509#

The 2950's Gi0/1 config is:

switchport mode trunk

no ip address

...and MAC address of this interface is 000c.8509.170d (Vlan1 MAC is .1700)

The 6509's Gi3/2 config is:

no ip address

no logging event link-status

switchport

switchport trunk encapsulation dot1q

switchport mode trunk

I must be missing something. Why wouldn't (a) the mac address appear both in the correct "show mac int" as well as "show mac vlan" output, and (b) the mac address stay in the table for the full 300 seconds?

Thanks in advance for any insight.

Craig

[ovt]

1. If "Vlan1 MAC is .1700" why is:

Cat6509#sh mac int gi3/2 | inc 000c.8509

* 1 000c.8509.170d dynamic Yes -- Gi3/2

* 133 000c.8509.1700 dynamic Yes -- Gi3/2

^^^^^^^^ - this mac appears to be in the vlan 133 !!!

2. Switch may flush MACs earlier than 5 mins. This is normal. This happens when topology changes.

[cghareeb]

1. The only two vlans that are up on the 2950-12 are 1 and 133 - both are represented by the same MAC (.1700).

2. I'm not positive I'm clear on what you mean by "topology changes". Looking at the spanning-tree detail of the 2950, the VLANxxxx interfaces report "Number of topology changes 2 last change occurred 5w5d ago" (which is farther back than my session log) the fa and gi interfaces all show "Number of transitions to forwarding state: 1". I'm not sure where else to look for data on topology changes.

[ovt]

1. It seems that 2950 sends frames using vlan 133 interface, rather than vlan 1 interface. That is why it encapsulates them into 802.1Q using 133 in "vlan-id" field of the 802.1Q header. Check "sh ip int brief" and "sh ip route" on the 2950.

2. Use "sh spanning-tree vlan 1 detail" and "sh spanning-tree vlan 133 detail" on the 6500 (not on 2950) to check when the last topology change occured.