21 minute Wireshark?

[dbronco]

I've been investigating multiple networking problems at one of our sites and have come across something I don't quite understand and am hoping someone here can point me in a direction. 

This site has 350 cameras and 5 subnets - 4 subnets for the buildings and 1 subnet for the switches

I started running Nmap scans (regular scan) on each subnet and had the following results (from the sh tech you'll see I missed VLAN36) 
VLAN30 - 117 devices - 21 minutes
VLAN31 - 117 devices - 85 seconds
VLAN32 - 67 devices - 51 seconds
VLAN33 - 9 devices - 15 seconds
VLAN34 - 33 devices - 50 seconds
VLAN55 - 86 devices - 48 seconds

I validated the 21 minute scan from two separate workstations as well, one on the same subnet and one on a different one. How can I start investigating what is going on with VLAN30? 

[pieterh]

the show tech does not show issues at first glance

1) did you mean : what is going on with VLAN36 ?
2) can you access the camera's on this vlan ? (can you open a stream, can you ping a camera

if yes, => I suggest to first check your scan command, not the config of your switch
you should at least find the ip-address of your switches vlan interface

if no => check the ip-settings configured for this vlan (gateway/netmask)
if this does not not match, then response does not return to your nmap device

[dbronco]

Hi pieterh, 

Thanks for the response. I could've been more clear in my question, rather than the title. My question is why is VLAN30 taking 21 minutes to complete while all my other VLANs, take around 90 seconds? It has the same amount of devices as VLAN31 but too a full 20 minutes longer to complete. The same scan was ran for all VLANs.

And to follow up - yes, I can access all cameras on this VLAN? They are recording, live stream is fine, they PTZ, etc.