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Forum Discussion
Solved
Cable Issue?
Switch1: GS752TPv2
Switch2: GS724TPv2
I have the above switches connected using SFP ports, and in each port, I have the same module and fiber patch cable from FS.com:
SFP Module: https://www.fs.com/products/13282.html
Patch Cable: https://www.fs.com/products/88527.html
In Switch1, ports 50 & 52 (bottom SFP ports) are setup in a LAG.
In Switch2, ports 25 & 26 are setup in a LAG.
When I connected the fiber cables (nothing else connected to Switch2), I experience weird network issues:
- Some devices on Switch1 could only communicate on the LAN and couldn't hit the FW and get out to the Internet.
- For devices on Switch1 that could still get to the Internet, running a continuous ping would result in frequent dropped packets.
- The ports on Switch2 would eventually disable.
- I disconnect one of the two fiber cables, the issues resolve.
FWIW, I have this same configuration on different floors of our building. The 26 port switches are new to support a new camera system, but in each case are connected to a different 52 port switch, but in the same fashion. They both show similar behaviors when both fiber cables are connected.
As I'm looking at the cable and module specs, did I get the wrong cables? Oddly, at a different location, I have two GS752TPv2 switches connected with the same modules and style cables (just twice as long, ~3ft).
In this configuration, should I have gotten these instead:
https://www.fs.com/products/40180.html
This are MMF (Multi Mode) modules, while the fiber is SMF (single mode). A SMF fiber core is just 9 um (in the 125 um total glass cover), while MMF is 62.5um core (OM1) resp. 50um core (OM2 or better) both in 125 um glass cover. So yes, wrong patch cable.
9 Replies
This are MMF (Multi Mode) modules, while the fiber is SMF (single mode). A SMF fiber core is just 9 um (in the 125 um total glass cover), while MMF is 62.5um core (OM1) resp. 50um core (OM2 or better) both in 125 um glass cover. So yes, wrong patch cable.
I chatted with FS and they said the same thing.
However, any thoughts on why this seemingly works on two connected GS752TPv2 switches?
Same modules, same cables (just longer, ~1m/3ft). That's why I purchased the same items.
Or is this a case where maybe it's not working like I'd think, and I'm not getting the benefits of LAG but the switch has error correcting to where it's not disrupting normal communications? I don't know, I was just surprised that it appears to be working in two other instances. I've ordered the multimode cables.
Rneal1973 wrote:
However, any thoughts on why this seemingly works on two connected GS752TPv2 switches?
Same modules, same cables (just longer, ~1m/3ft). That's why I purchased the same items.
There are some theories and practical hints about mixing MMF modules and MMF and SMF fibers around. The "trick" is to use longer (I remember having used some 10 meters of SMF) to "focus" the light while reducing reflections from the "outer" mechanical glass carrier. Think bout that both types re built on a 125 um outer carrier glass "tube" holding the effective 9 um (SMF) resp 50/62.5 um inner thin fiber effectively used for the transmission/reception.
The fiber we see is always the complete 125 um diameter glass "tube", while the effective transmission and TX/RX optics is optimized for 9 um resp. 50/62.5 um.
https://community.fs.com/article/single-mode-cabling-cost-vs-multimode-cabling-cost.html shows the effective diameters FWIW.
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