2950 switches mac table learn issue

[rijalsaroj]

I have 2 cisco 2950 switches lets name A and B. A is uplink switch of B. In switch B two client are connected in same VLAN. clinet1 mac address is learned in switch A but Client2 mac address is not learned in switch A. Mac table of switch is not full   What is the issue behind this?

[M02@rt37]

Hello @rijalsaroj,

Is it a Trunk between the two switch?

If the connection between Switch A and Switch B is a trunk link, verify that the trunk configuration is correctly set up on both switches. Make sure the appropriate VLANs are allowed and that the trunk is operational.

Also, ensure that both switches, A and B, have the same VLAN configuration for the ports where Client1 and Client2 are connected. If they are in different VLANs, the MAC addresses will not be learned across the switches.

[rijalsaroj]

yes it is a trunk. client 1 and 2 are connected in same VLAN. trunk configuration is correctly set up on both switches and same VLAN is allowed.

[MHM Cisco World]

Show interface switchport x <- share this for interface connect two client 

[rijalsaroj]

Switch A
Name: Fa0/7
Switchport: Enabled
Administrative Mode: trunk
Operational Mode: trunk
Administrative Trunking Encapsulation: dot1q
Operational Trunking Encapsulation: dot1q
Negotiation of Trunking: On
Access Mode VLAN: 1914 (POP-VLAN)
Trunking Native Mode VLAN: 1 (default)
Voice VLAN: none
Administrative private-vlan host-association: none
Administrative private-vlan mapping: none
Administrative private-vlan trunk native VLAN: none
Administrative private-vlan trunk encapsulation: dot1q
Administrative private-vlan trunk normal VLANs: none
Administrative private-vlan trunk private VLANs: none
Operational private-vlan: none
Trunking VLANs Enabled: 656,1914
Pruning VLANs Enabled: 2-1001
Capture Mode Disabled
Capture VLANs Allowed: ALL
Protected: false
Appliance trust: none

Switch B

Name: Fa0/13
Switchport: Enabled
Administrative Mode: trunk
Operational Mode: trunk
Administrative Trunking Encapsulation: dot1q
Operational Trunking Encapsulation: dot1q
Negotiation of Trunking: On
Access Mode VLAN: 1 (default)
Trunking Native Mode VLAN: 1 (default)
Voice VLAN: none
Administrative private-vlan host-association: none
Administrative private-vlan mapping: none
Administrative private-vlan trunk native VLAN: none
Administrative private-vlan trunk encapsulation: dot1q
Administrative private-vlan trunk normal VLANs: none
Administrative private-vlan trunk private VLANs: none
Operational private-vlan: none
Trunking VLANs Enabled 656,1914
Pruning VLANs Enabled: 2-1001
Capture Mode Disabled
Capture VLANs Allowed: ALL
Protected: false
Unknown unicast blocked: disabled
Unknown multicast blocked: disabled
Appliance trust: none

[M02@rt37]

@rijalsaroj,

The port SwitchA-FA0/7 seem to be int Trunk and Access mode.

It's not normal for a port to be configured as both a trunk port and an access port at the same time. In the configuration you provided SwitchA-FA0/7, the administrative mode of the port is set to trunk mode, and an access VLAN (VLAN 1914) is also specified.

To correct this issue, you should remove the access VLAN assignment and ensure that the port is correctly configured as a trunk port. You may also want to review the configuration of other ports on the switch to ensure that they are correctly configured as access (only) ===> The port where the client are connected with the good VLAN id. Because your are on L2, the client has to be on the same VLAN. And this VLAN id should be added to the Trunk beween Switch A and Switch B.

[MHM Cisco World]

Friend I need to see port connect to host and also

Show interface trunk 

Thanks 

MHM

[M02@rt37]

Ok @rijalsaroj,

Please share the output:

#show interface status

#show interface trunk

On both switch.

Thanks.

[rijalsaroj]

switch A

show interface trunk  Fa0/7 656,1914
show interface status Fa0/7  connected trunk a-full a-100 10/100BaseTX

Switch B

show interface trunk Fa0/13 656,1914
show interface status Fa0/13  connected trunk a-full a-10 10/100BaseTX

[M02@rt37]

Hello @rijalsaroj,

Thanks for the output.

What about the ports where the client are connected? 

Please share the conf and the status of that ports.

[Joseph W. Doherty]

If both clients are connected to switch B, and in the same VLAN, also known to switch A, it's possible switch A does learn of both clients MACs, but ages one client's MAC out because that client's traffic stays local to switch B while some of the other client's traffic does not.  I.e. can be normal/correct behavior.  Insufficient information to say for sure.

Unlikely to be your situation, but if you research unicast flooding, you'll find, possibly, an unexpected issue between switches with different MAC tables yet "correctly" working.

[Richard Burts]

I believe that Joseph is on the right track with his suggestion that the client on switchB may have traffic that stays local, and in that case switchA would not learn its mac address. What can you tell us about the device in switchB? Is it some computer, or a server of some type, or some specialized device? 

Is the device on switchB able to do what it is supposed to do? If so then the fact that its mac address is not learned on switchA is not a problem.