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NewBie CRS305 issue

Tue Sep 22, 2020 6:00 am

Hi all,

I recently purchased a MikroTik CRS305-1G-4S. I'm running SWOS 2.12. I have no VLAN's other than the default. It's a flat network connecting 3 PC's together on the same IP Subnet. All 3 pc's have 10GTek SFP+ NICS. 2 pc's have MikroTik transceivers and 1 has a MikroTik 2 meter DAC. The CRS305 has all MikroTik transceivers as well. The issue is the pc with the MikroTik DAC works flawlessly dropping NO packets. The other 2 are using 5 meter fiber cables, LC to LC Multimode OM3 Duplex 50/125 OFNP. The 2 using the fiber cables constantly loses connection and drop 10 out of every 100 ICMP requests.

All I've done on the CRS305 was change the IP to Static, boot to SWOS, upgrade it to 2.12, change it's IP to static as well to match the IP Subnet the 3 pc's are on. For what it's worth they all show up fine in SWOS whether they are the 1 DAC transceiver or the 2 fiber ones. I've tried different fiber cables, SFP+ modules (transceivers) and the result is the same, the fiber based NIC's all start flapping. I've verified that the NIC settings are exactly the same on all 3 NICS other than IP of course. Any guidance would be appreciated.
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Re: NewBie CRS305 issue

Wed Sep 23, 2020 2:28 am

You did not tell us what fiber SFPs you are using. You did specify that the ones having problems are using multi-mode FO cable. Makes me wonder if there is a mismatch between multi-mode and single-mode - either with the jumper cables or with the SFPs. From what you said, I am gathering that you are using 10Gb/s links, and as I recall, most 10G FO links are single mode. Single-mode and multi-mode don't mix well together.
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