Ethernet Interfaces – Understanding eth/in, eth/out, eth/local

Finally solved! i don't know why but an other interface was set in DHCP mode (not allowed in here, only static addresses can go to the WAN), i disabled this interface and things got back to normal. Thank you everyone for your answers

There would be a number of ways to do this that are better than the way you are currently doing it. Pick from any below that fits your circumstances and access.

1. If all the IP cameras communicate with a server on the same L2 network, then the server should have all the cameras in it's ARP table already. Simply pull the ARP table on the server.
2. If you know all the IP addresses of the cameras AND can connect your laptop to the same L2 network, then simply ping each camera from the laptop and check the ARP table. You can do this from any MDF/IDF if they are all on the same L2 network as you say they are all connected back to the MDF. Entries in the ARP table will age out within a couple minutes, so you may need to be quick about it.
3. If you don't know all the IP addresses of the cameras AND can connect your laptop to the same L2 network, then run a utility that can ping a range of IP addresses quickly (Angry IP Scanner for example) that covers the L3 network and then check the ARP table. If your cameras are all similar manufacturer and model, they will likely share the same OUI (first six digits fo the MAC address).
4. If the cameras communicate using a L3 gateway/router and you have access to the router, then you may be able to access the ARP table from the router.
5. If the cameras get their IP addresses from a DHCP server, then you can get the MAC addresses from the leases/log on the DHCP server.
6. If the network has a management/monitoring system, then you may be able to get the MAC addresses from the management/monitoring system.
7. If the switches are managed AND you have access the the switches' management interface, then you should be able to get the MAC addresses from each switch. As this may require accessing each switch, this may be a bit more involved than some of the other options.

These are the ways I came up with without thinking on it too much that would all be better than going to each IDF. I am sure others will have more suggestions as well.

If I plug my laptop directly into the switch at the IDF, or even the switch at the MDF, that will put me on the same LAN as the cameras, if they're all connected via switches, right?

Not necessarily. The network can be separated into multiple VLANs or the links between MDF and IDFs can be L3 links. Either way, you may not be on the same LAN by connecting at one point. You would need more information about the network to know this answer.