There are lots of cheap and not so cheap ethernet surge suppressors that aren't super effective. You want one that has both gas discharge tubes, and preferably "diodes"/MOV. You want one that will attenuate both line to line (across the Ethernet signal wires) and lines to ground.
I used these;
https://www.amazon.com/Tupavco-Ethernet-Protector-Gigabit-1000Mbs/dp/B00805VUD8/
the ground wire is way too short and I ended up creating a ground bus for a couple of ethernet cables entering the house at the same point, and then a heavy ground wire back to the main electrical panel.
Downstream, I added an MOV based unit.
Like this one;
Amazon.com: Qooltek ST-NET Ethernet Surge Protector for 10/100/1000 Base-T PoE+ Gigabit Modem Thunder & Lighting Protection ST-RJ45 : Electronics
www.amazon.com
(I am amused at the "thunder" protection, but it does contain diodes for fast clamping.)
All of the units that I looked inside had thin little PCB traces to carry the lightning surge, which is pretty pathetic in my opinion, but again, these gizmos are to take the edge off a surge, not stop a nearby strike. If you have a close hit, lots of things are going to vaporize.
You can get "outdoor" versions that are helpful to put on Ethernet cameras and WiFi access points/antennas. They have varying degrees of water resistance, but I use them as well to provide voltage clamping on both ends of every ethernet cable entering or leaving the house to keep any transient voltage surge as small as possible.
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@grsthegreat, I put in the Siemens 140; cheap insurance in my book. I do have another half a dozen outlet surge suppression strips scattered around the house. Each one of them helps attenuate surge as well. (Each is another 4,000J, supposedly.)
All the best,
Peter