I'm currently trying to setup zoneminder on my computer that has Ubuntu as a host OS.

Before I do all that, I want to know if the poe CCTV camera I purchased works, a Reolink RLC410-5MP

There are multiple ways to achieve this but the simplest one I found was to use the rstp URL in VLC After searching the correct format for the URL, this is what I found

Main Stream: rtsp://admin:password@ip_address:554//h264Preview_01_main

What I need now is the IP address of the CCTV, which is connected directly to my laptop via an Ethernet cable and is being powered by a power supply

I'm not 100% sure how to find the IP address, one way I found is using

nmap -sn

However the above shows 8 devices connected and I'm puzzled as I should be only expecting one/two devices(the CCTV and maybe the router?)

What's the best way to find the IP address of a poe device physically attached to a laptop via an ethernet cable?

  • 1
    Does the device get IP via DHCP? If so, simply check the DHCP servers lease file. – vidarlo Jun 1 at 19:10
  • I'm not sure what you mean via the DHCP, how do I check this? – Sgr Jun 1 at 19:14
  • 1
    How does the device get a IP? Does it have a standard IP? Does it use DHCP to acquire the IP? Did it have a previously set IP address? Does it fall back APIPA if there's no DHCP? – vidarlo Jun 1 at 19:16
  • I'm not that familiar with this process, all I know that POE devices get an IP address autoatically, I used this guide that is for windows but gives some info on how poe devices works, reolink.com/connect-security-ip-camera-to-pc I looked a method 1 – Sgr Jun 1 at 19:24
  • No, there's no mechanism in Power Over Ethernet for assigning IP addresses. Network devices commonly use DHCP to automatically get IP's. Unless DHCP is used, the process will differ from manufacturer to manufacturer. – vidarlo Jun 1 at 19:26

For the situation where you attach an unknown device directly to your computer (laptop), the first thing to try is to run a DHCP server on your computer and give it an address.

The you look at the log of the DHCP server and you'll know which address it has.

The DHCP protocol works very roughly like this: A device broadcasts a "hello, I'm new in this subnet! Can anyone give me an IP address?" message, and the DHCP server answers "welcome, new device, here is your IP address in this subnet, and other network information you may find useful".

Details how to run and configure a DHCP server depend on your distro. I am using Debian, running the isc-dhcp-server package, which is configured in /etc/dhcp/dhcpd.conf and logs to syslog.

The fun starts if the unknown device is not using DHCP, but instead gives itself a static IP address. Then you read the manual, or indeed you run nmap, interprete the answer(s) and try more things to find out what the device does in detail.

  • As an alternative, if the hosts are on the same link, you can use mDNS or LLNMR (Link-local Multicast Name Resolution). These mechanisms work roughly like this: the client sends a multicast message "I want to talk to host A", host A responds "That's me, here is my IP address". – Johan Myréen Jun 2 at 7:04
  • @JohanMyréen Though if a decice supports mDNS, it will likely also do a DHCP request, while on the other hand there are devices that do only DHCP requests (it's the simpler protocol), and don't offer mDNS. So I'd try DHCP first. – dirkt Jun 2 at 8:24
  • On the other hand, mDNS also works with autoconfigured addresses, and link-local (IPv6) addresses. – Johan Myréen Jun 2 at 11:14

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