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How can you identify the mac address at both ends of a trunk?

How can you identify the mac address at both ends of a trunk port on a catalyst 3500XL switch?

thanks in advance

mlj

4 REPLIES

Re: How can you identify the mac address at both ends of a trunk

Hi,

I'm not sure if I understand your question correctly.

Do you want to see the MAC address of the trunk port?

If yes, use sh int command on both ports connected via the trunk.

Example:

sh int gi 0/2

GigabitEthernet0/2 is up, line protocol is up

Hardware is Gigabit Ethernet, address is 0004.c15c.5d32 (bia 0004.c15c.5d32)

The bia means Burnt In Address - it can be changed via sw for some reasons but usually you see the actual address (the first value) be the same.

But the MAC address of the switch port is almost never used. The only case is a source address in frames of traffic generated from the switch itself - CDP, VTP, STP BPDUs, ping, Telnet, etc.

Regards,

Milan

New Member

Re: How can you identify the mac address at both ends of a trunk

Hi,

In fact i am auditing a cluster of switches without the ability to see the devices. When i run 'sh cdp ne' on all the clusters so far I follow the cabling by the interface the switch is seen through:

SW002C Gig 0/8 175 T S WS-C3508G-Gig 0/8

SW003 Gig 0/1 179 T S WS-C3524-XGig 0/1

SW-004 Gig 0/3 169 T S WS-C3524-XGig 0/1

SW-001 Gig 0/4 144 T S WS-C3524-XGig 0/1

SW-004 Gig 0/2 149 T S WS-C3524-XGig 0/1

but on the last cluster all switches are seen as connected to 1 switch when it does not have enough ports forthis configuration. So I do not know how to verify which switches are connected to each other.

SW-002C Gig 0/2 123 T S WS-C3524-XGig 0/2

SW-001C Gig 0/2 168 T S WS-C3524-XGig 0/2

SW-004 Gig 0/2 162 T S WS-C3524-XGig 0/2

SW-006 Gig 0/2 131 T S WS-C3524-XGig 0/2

SW-007 Gig 0/2 152 T S WS-C3524-XGig 0/2

SW-003 Gig 0/2 172 T S WS-C3524-XGig 0/2

SW-008 Gig 0/2 131 T S WS-C3524-XGig 0/2

It seems that the trunks are connected in a strange configuration.

any ideas.

mlj

Re: How can you identify the mac address at both ends of a trunk

It's really strange...

If you do sh cdp nei on SW-001C do you see all the other switches, too?

If yes, it seems like all the switches beeing interconnected via some "optical hub" or unmanagable switch.

I would try to shutdown one port or reload one switch to see if any port on any other switch goes down in the same time. If not, there is definitely some "no point-to-point" cabling and I'm afraid the only chance to discover it is to go and watch the cabling on the site personally.

Regards,

Milan

New Member

Re: How can you identify the mac address at both ends of a trunk

Hi,

I am now aware of the issue. It seems the switches are configured in a stack but each switch has only 1 GBIC. The GBIC are used in Half duplex mode and are connected up and down.

This meens that on all switches the sh cdp ne commands shows all switches

out GI0/2 which is correct. The sh cdp ne does not show which port on the GBIC so it is impossible to the topology.

Reference cisco document.

http://www.cisco.com/en/US/products/hw/modules/ps872/products_data_sheet09186a00800a1789.html

I would still like to know if its possible any otherway. May be this issue is resolved in a new version of the IOS.

current version Version 12.0(5.4)WC(1)

regards

mlj

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