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TOPIC: Port uptime

Port uptime 11 years 7 months ago #22046

  • Attish
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Hi All!

Given a switch (Cat 3560) with plenty of servers and desktops connected to it. We are planning to put the servers on a different VLAN, so I have to find out which cables go to which. I could track down the cables physically but it does not sound too techy. That is why I thought I am going to differentiate them by trying to find out what their MAC addresses are by using "sh arp", but again I found that both the servers and the desktops (Dell) use the same first 6 character in their MAC addresses.
Then I thought that if I could find out how long the port has been active, I could tell the difference between servers and desktops. So here is the question:
Do you think there is a command which shows you the port uptime?
On the same note, is there a way to find out when a port was last active?

Any help is most welcomed!



Re: Port uptime 11 years 7 months ago #22047

Can't think of a command that will do this for you, however you might want to try this: Come into work (or stay a little late) when all the other staff have gone, and check the port lights on the switch. Since all your desktops will (should!) have been shut down for the night, the ones left active are your servers

Re: Port uptime 11 years 7 months ago #22049

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You could possible do this if you monitored the switch using SNMP/SYSLOG. Problem is that you would need to go through the logging. We use SolarWinds Orion using SNMP traps, this tells us when a port goes down and when a port comes up.

Wayne Murphy Team Member

Now working for a Security Company called Sec-1 Ltd in the UK, for any
Penetration Testing work visit or PM me for details.

Re: Port uptime 11 years 7 months ago #22051

'show arp' and 'show mac-address-table' will tell you what is plugged in each port, assuming you know, or can get, the mac-addresses of the servers.

the first 6 digits of the mac are useless. You need to use the last 4-6 digits.

Always label your ports with 'description' command- it will save you time and headaches. Also, if the switch is being shared between servers and workstations, it is a good idea to keep like connections together-- personally, servers and workstation don't belong on the same switch, but that can't always be avoided, so if you have 10 servers physically layout the connections so that all of the servers are together at one end of the interface range.

example- use port one for network uplink, ports 3-10 for servers, and 11-24 for workstations. This will also save time and headaches.

Design your networks, don't just plug stuff in without thought.

Re: Port uptime 11 years 7 months ago #22146

This is what I do if I need to find which port a device is in based on MAC address.

Assume MAC Address is: 00-07-E9-EC-F8-07

I would then issue the command:[code:1] show mac address-table | inc F807[/code:1]

This will display the mac address-table and then filter the results to only include entries that have F807.
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