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Jon Marshall Tue, 07/03/2007 - 03:34
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Hi Ali

What is gigabit 0/1 - is it a trunk link to another switch ?


mahmoodmkl Tue, 07/03/2007 - 03:36
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What is the configuration of this ports i mean r they trunk ports or access ports.



smothuku Tue, 07/03/2007 - 03:46
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Hi ,

I also observed it on my 3750 switch (L3)...

different mac-address are assigned to same interface...

copy the mac-address and do the sh arp | in mac-address for g0/1. Do it for all mac-addresses ..you will get the exact IP for only one mac-address, not for all...

pl clear mac-address table and check the issue...

I observed that when there is a fluctuation or flap in network we will get this type of output.

cheers :)


royalblues Tue, 07/03/2007 - 06:07
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I seriouslt think the link in question is a trunk.

Satish, i have not seen this type of behavior on the 3750 switch. You will multiple mac-addresses on the port connecting to a router and also a SVI configured on the switch for the same subnet.

The ouput on the other hand shows mac-addresses and that too in different vlans which should be possible only when the link is a trunk

can you post output of sh int g0/1 switchport



Sorry this is a Trunk port...

sh int g0/1

GigabitEthernet0/1 is up, line protocol is up

Hardware is Gigabit Ethernet, address is 0002.b9b8.cd31 (bia 0002.b9b8.cd31)

Description: To xxxx

MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec,

reliability 255/255, txload 1/255, rxload 1/255

Encapsulation ARPA, loopback not set

Keepalive not set

Auto-duplex (Full), link type is autonegotiation, media type is SX

output flow-control is off, input flow-control is off

ARP type: ARPA, ARP Timeout 04:00:00

Last input 00:00:01, output 00:00:00, output hang never

Last clearing of "show interface" counters never

Queueing strategy: fifo

Output queue 0/40, 0 drops; input queue 0/75, 0 drops

5 minute input rate 6961000 bits/sec, 7683 packets/sec

5 minute output rate 61000 bits/sec, 62 packets/sec

152984413 packets input, 1546610108 bytes, 0 no buffer

Received 117454707 broadcasts, 0 runts, 0 giants, 0 throttles

0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored

0 watchdog, 74766732 multicast, 0 pause input

29242288 packets output, 381330967 bytes, 0 underruns

0 output errors, 0 collisions, 1 interface resets

0 babbles, 0 late collision, 0 deferred

0 lost carrier, 0 no carrier, 0 pause output

0 output buffer failures, 0 output buffers swapped out

NoW its become Clear,can i know the Reason and How to Solve This?


royalblues Tue, 07/03/2007 - 09:17
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Since the trunk port is connected to another switch, it will learn all the mac-address from the downstream switch on that port.

say if you have a router connected to switchA and has a trunk connection to switchB, then switchA should know all the mac addresses for the nodes on switchB for forwarding frames that are sent from the router to these devices

HTH, rate if it does


Amit Singh Tue, 07/03/2007 - 09:26
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Hi Ali,

How are you !!

Could you please try clearing the mac-address table using " clear mac-address table " command and check if still shows the same mac in different vlans on the trunk port. One of the reason for this would be if there is a user who is connecting his PC in different switchports which belongs to different vlan, then the same mac-address might be see on the different vlans


-amit singh

Amit Singh Tue, 07/03/2007 - 09:35
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Hi Ali, I am fine and doing well.. How are you doing.. I will pass on your message to Ankur. he is very busy now a days..

Did you clear the mac-address table ? Check and update us on the status.

-amit singh

smothuku Tue, 07/03/2007 - 20:41
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Hi Narayan ,

I've small doubt..In which situation we will get multiple mac-addresses for same port...

Cheers :)



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