I have a Cisco C3750V2 switch in which a particular interface is continuously flapping almost i could find 15,000 events from the device logs in last 24 hours. Is there a way to find the end device connected to this particular interface??
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Did any answer help you? if so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could provide and accept your own answer.– Ron Maupin ♦Aug 12, 2017 at 20:32
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4 Answers
Use CDP.
Show cdp neighbors will show you the name of the device on the interface
Of course thats only if CDP is turned on on both devices.
First you need to check which is the interface that isn presenting the flapping event. Then you can write:
sho mac address-table
To see de mac address table and find the mac address learned by the flapping interface in particular.
Next, you can visit here:
www.macvendorlookup.com/
or something else, to make a lookup for the vendor of that specific mac address.
Finally, you will find de device, i hope so
Remotely? That's hard to say. As Orlando suggests, the MAC could point you in that direction (nic manufacturer.) If the device and switch are setup for LLDP, that may give you a better picture. Setting up a SPAN to watch any traffic on that port may be enlightening.
Ultimately, you go to the end of the cable connected to that port and see what's there. However, that requires you to be on-site and the device causing the problems being there when you arrive.
Finding the switchport a device is connected to is very easy. You can do it using the following commands:
traceroute
show ip arp <ip_address>
show mac add <mac_address> | show mac-add add <mac_address>
The last command depends on what version of IOS you're using.
If you need additional information I have just published a blog post describing how to achieve what you're asking - http://www.oznetnerd.com/2015/10/30/finding-a-hosts-switchport/
By the way, what exactly does the event/log say? It should really give you all the information you need. e.g if it were a MAC flap, it should tell you the ports its flapping between. If it is a physical port flap, it should tell you the exact port number.
