how to discover a L2 vlan information?

[baselzind]

I have some old L2 vlans which i have no idea whether they are still in use or not. Is there a way with a packet capture software to find out what devices are connected to this vlan and what are their ip addresses?

[marce1000]

  -   From the (a) core switch you could do "show mac address-table vlan vlan-id" and "show ip arp vlan vlan-id" ; now that is like taking a photograph (only) , from a business perspective targeting objectives and good network management is better, such as abandoning or deleting the vlan if it is considered not needed.  Because any host can simply be in 'deep sleep' or use the network periodically (e.g.). Then sufficient 'user management' includes notification procedures to users when there are network changes (e.g2)

 M.

[Flavio Miranda]

Hi

  The only software I know that could help would be Wireshark. You can span a trunk port, uplink is better, and send to a port connected to a PC. On the PC, running wireshark, you can see if the host , the vlans, if they are sending traffic, the port, mac address etc.

 You may need to apply filters on Wireshark.

[MHM Cisco World]

this VLAN have subnet ? if Yes then ping broadcast of subnet if you receive reply then there is still some device connect to this subnet.

You can also use 

Show mac address table 

It list the mac port and vlan 

If you see mac appear in with this old vlan then there active device connect to this vlan.

[M02@rt37]

Hello @baselzind,

To determine which devices are connected to a specific VLAN and their IP addresses, you can use a packet capture software to analyze the network traffic --- Wireshark as @Flavio Miranda suggest to you.

Analyze the captured packets by examining the source and destination IP addresses. Look for packets that have a source IP address within the range of the VLAN you are investigating. These packets indicate devices that have sent traffic from the VLAN. Note down the source IP addresses and analyze their traffic patterns to identify the active devices on the VLAN. You may be able to determine the device type or hostname from the captured packets.

[Leo Laohoo]

How big are the subnets of this VLAN? 

Find an IP address scanner and determine if there are any host(s) still pinned to the VLAN.  Find the owner of said host(s).

[baselzind]

thanks everyone for their input. My main issue with this vlan is that it is unknow and it is L2 so there is no SVI and i dont know what subnet it uses or if there users on the subnet , and even if i use the Wireshark there is no seen traffic so is there somekind of tool that will trigger all hosts on the subnet to reply with their ip? 

[Leo Laohoo]

Search for the term "ip address scanner". 

[Richard Burts]

The original post asks if packet capture is a way to identify whether some old L2 vlans are still in use. I believe that the consensus of the responses is that packet capture is not an effective tool for this. There are other approaches that are more likely to provide useful information. My suggestion would be to go to the devices that are providing L3 routing for the L2 switches and do show arp an look for any mention of the old L2 vlans.