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SFP modules convert electrical data from the equipment to optical signals. There is no incoming power surging from an optical port to damage the equipment according to my undarstanding of fibre optics. SFP draws voltage/power from the equipment itself. So can wrong or incompatible SFP modules or cables damage the equipment itself, such as switches or network adapters or is the possible damage exetent is from the SFP module to the SFP module and the network equipment is safe from harm ?

SandShriner
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In principle, it should be possible to create a malicious device in the SFP form factor which can damage the device you plug it into, the same way as USB stick of death does it. SFP can draw maximum of 2W total (3.3V, two power supply pins, 300 mA maximum per pin), so it is harder to do than with USB, though.

Other than that, if you take a module from a respectable vendor that participate in SFP MSA, the worst problem you can face is that module won't work. It will not damage a host equipment nor it will be damaged itself. There is still a concern with the heat dissipation. SFP modules can get pretty hot and if your module exceeds the device cooling capacity, it will overheat. But most decent modules have thermistors so to shut down on overheating to prevent damage.

You can even hot plug and pull them.

Nikita Kipriyanov
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  • Can this type of overheat damage a switch or network adapter that the spf is connected to ? – SandShriner Jul 07 '23 at 02:28
  • Moreover, what is the proper way of matching equipment cooling capacity and spf? Is it something worth doing or the overheating problem is an edge case not worth looking at? – SandShriner Jul 07 '23 at 02:49
  • It shouldn't. The only way of matching is to read specifications. I've seen cases when *faulty* module overheated and shut down, so it was replaced with the same model module and that worked perfectly. If you want **any** prior guarantees, you have to only use modules which are listed by the vendor as compartible; in some cases that will make you pay more for them. Then if something goes wrong you'll have someone to blame — the vendor. – Nikita Kipriyanov Jul 07 '23 at 03:26
  • In my environment, there is only one spf+ connected at a given time on a switch that is capable of much more network connections. It should not overheat if I understand correctly. Neither the device nor the spf module (except if it's faulty). Please correct me if I'm wrong. – SandShriner Jul 07 '23 at 03:57
  • The dissipation of the heat from the module is up to the host device. If the slot is not designed to dissipate enough, the module will overheat, even if it is good. Consider an "[unnofficial workaround](https://community.cisco.com/t5/switching/sfp-overheating/m-p/814993/highlight/true#M34541)" Cisco TAC suggested for the case as an example. Also look [here](https://serverfault.com/questions/715382/cisco-1000baset-sfp-modules-in-a-3750-overheating) to see how the problem can manifest itself. – Nikita Kipriyanov Jul 07 '23 at 05:42
  • The unofficial workaround of cisco fits my logic, that if there is a switch designed to cope with 16 connections, like mine, and in reality only one sfp cable is plugged in to slot - the other 15 are empty and nothing is connected to them, it's pretty much dissipating, it should. – SandShriner Jul 07 '23 at 06:06