Jan 142013

How to see which VLANs are currently used on a trunkport on a switch?

Easy Answer:
Do a show mac address-table interface <interface>

and you will get a list of VLANs with MAC addresses used. Of course, any VLAN that have MAC-addresses associated, is in use.

That’s an easy way to find out which VLAN-tags are currently running over a trunk. (keep MAC-address aging timer in mind)

 Posted by at 12:23
Mar 172010

Worried about the following error-message while plugging in a TwinGig Converter Module (CVR-X2-SFP) in a Catalyst 4500?

%C4K_TRANSCEIVERMAN-3-SEEPROMREADFAILED: Failed to read transceiver serial eeprom on port Te5/3, try reinserting

This is really not a serious problem although it looks like one. You just have to configure your TenGigE-Port to GigE. On a 6Port 10GE-Linecard (WS-X4606-X2-E) it is important, that you can only put 3 ports in 1GigE-Mode at once. Each 3 Ports are grouped together to one Port-Group. If this is a problem you can deal with the TenGigE-Ports on your Sup (depending on the Sup you are using…)

You can have the following configurations on a WS-X4606-X2-E:

  • 6 TenGigE
  • 3 TenGigE, 6 GigE
  • 6GigE, 3 TenGigE
  • 12 GigE

To switch a Port-Group over to 1 GigE use the following command:

hw-module module 5 port-group 1 select gigabitethernet

This will put your 1st three ports on the Module in Slot 5 into Gigabit-Mode and voila – your TwinGigConverterModule will no longer be rejected with this crazy errormessage.

 Posted by at 19:50
Oct 212009

Did you ever have the problem that your switch didn’t learn the MAC-addresses of the connected devices on one of its switchport? All cabling seems all right – Link is UP – Port is connected.
But show mac address-table won’t show you the MAC of your device although it is sending packets.

Check your VLAN-config!

If your switchport is configured to a VLAN thet doesn’t exists on your switch – then the switch won’t learn anything on this port. This could only happen if your switch is in VTP mode “client”.
Otherwise the VLAN will be created automatically.

 Posted by at 14:06