I got the new M4 Mac mini with 10 GbE since my internet access is 1.9 Gbps down. I connected it up to my CAT5e and it negotiated and ran fine with a 2.5 Gbps link... until it didn't and dropped down to 1 Gbps. The CAT5e is good quality solid copper Belden DataTwist but part of the issue could have been my installation, since I did it myself DIY (almost 15 years ago). Jacks were CAT5e as well. The thing is that it's been running perfectly for that entire time at Gigabit speeds. Zero issues.
I had run CAT5e just because I had some left over from before. However, I did have the forethought to install another line in parallel, this one being some other lesser brand (not Belden) of solid copper CAT6, paired with CAT6 jacks. I'm not sure of the exact length, but I'm guessing they're about 50ish feet. Patch cable was also CAT5e, about 30 feet, so combined only about 80 feet or so. Note that the patch cable was actually DIY crimped as well, so again, installation may have been an issue. Nonetheless, I never had a problem running Gigabit, ever. No packet loss or whatever.
I switched over to the CAT6 line (which I also had installed myself), but kept the same CAT5e patch cable, and it seemed to solve the problem, negotiating at 2.5 Gbps and staying there. But just to be safe, I swapped out the 30-foot CAT5e patch cable for a 25-foot pre-made Monoprice CAT6 cable, and that also worked fine.
I was under the impression that 2.5 Gbps just needs the same 100 MHz frequency support as 1 Gbps and not more. However, I'd say that while in theory that may true, in real world practice, 2.5 Gbps may indeed need a bit more headroom than 1 Gbps. I realize it could have been a sub-par DIY install that was the problem, but as mentioned, Gigabit had no issues and my CAT6 install was DIY as well. IOW, it may be the case that CAT6 is more forgiving than CAT5e when dealing with even just 2.5 Gbps, even though CAT5e meets the specification.
I had run CAT5e just because I had some left over from before. However, I did have the forethought to install another line in parallel, this one being some other lesser brand (not Belden) of solid copper CAT6, paired with CAT6 jacks. I'm not sure of the exact length, but I'm guessing they're about 50ish feet. Patch cable was also CAT5e, about 30 feet, so combined only about 80 feet or so. Note that the patch cable was actually DIY crimped as well, so again, installation may have been an issue. Nonetheless, I never had a problem running Gigabit, ever. No packet loss or whatever.
I switched over to the CAT6 line (which I also had installed myself), but kept the same CAT5e patch cable, and it seemed to solve the problem, negotiating at 2.5 Gbps and staying there. But just to be safe, I swapped out the 30-foot CAT5e patch cable for a 25-foot pre-made Monoprice CAT6 cable, and that also worked fine.
I was under the impression that 2.5 Gbps just needs the same 100 MHz frequency support as 1 Gbps and not more. However, I'd say that while in theory that may true, in real world practice, 2.5 Gbps may indeed need a bit more headroom than 1 Gbps. I realize it could have been a sub-par DIY install that was the problem, but as mentioned, Gigabit had no issues and my CAT6 install was DIY as well. IOW, it may be the case that CAT6 is more forgiving than CAT5e when dealing with even just 2.5 Gbps, even though CAT5e meets the specification.
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