Need help with a difficult link, using CRS305 as a bridge

Hardware
1

I have been using a pair of S+RJ10 modules to connect two buildings via an existing direct-buried shielded Cat5e cable (shield is properly grounded at one end). The run includes a section of Cat6 cable that is patched to the Cat5e using a Cat7 connector. This connection has been working, giving close to GigE speeds (>900Mbps using iperf3). I know that the “right way” is to replace the Cat5e with fiber, but that’s not an option at this moment.

Common sense tells me that eliminating the Cat6 segment (replacing it with 10Gb fiber) should allow the S+RJ10 modules to achieve higher throughput across the shielded Cat5e. So I need to replace the Cat7 connector with a 10G SFP+ bridge of some kind.

I purchased a “10Gtek” 2-port SFP+ bridge off Amazon (https://a.co/d/033Lrr6X). This includes an LC fiber module and a 10GbE module, both “H!Fiber” brand. The 10GbE module is clearly a knockoff of the S+RJ10—looks identical, claims the same multi-speed connectivity. With the 10Gtek bridge and its SFP+ modules in place, I get a solid fiber connection, and the ethernet side connects intermittently, giving >3Gbps when it’s working. But it drops offline frequently. Replacing the H!Fiber 10G module with an S+RJ10, the link will not even come up. The link LED on the 10Gtek bridge comes on for about 5s, goes off for about 15s, and continues to do this indefinitely.

The 10Gtek module only officially supports the H!Fiber SFP+ modules, so I figured I needed a better bridge. I purchased a CRS305-1G-4S+IN. Updated to RouterOS 7.22.1 per instructions, left it at the default config which (according to the docs) should make it act as a standard 10Gb switch.

With the CRS305 in place, the link LED for the fiber link goes on and off, never giving a solid link. The USW Pro says RX error. I tried two different Ubiquiti fiber modules, as well as the H!Fiber module, but couldn’t get a working fiber link on the CRS305. Even more odd, the link LED for the S+RJ10 never lights up at all. Tried it in different ports on the CRS305, no joy. I did not have the CRS305’s GigE port connected, in case that matters.

I reinstalled the 10Gtek module (since it at least works intermittently), brought the CRS305 home with me, and created a supout.rif file—so the SFP+ modules were no longer installed, but it should at least show you the current config of the unit. If needed, I can reinstall the unit and pull a supout.rif file while everything is in place.

It's very strange to me that the CRS305 would not function better than the 10Gtek bridge—seems like it would at least link up at the physical layer—so I’m hoping that I’m simply not configuring the unit correctly. Anyone have any thoughts?

2

A supout.rif file is a "special" report file useful to Mikrotik support only, it is useless outside a support ticket AND it contains the WHOLE configuration of your device, so it is not a good idea to share it with anyone BUT official Mikrotik support.

What you should do is instead is to create and post an export file (.rsc) of your configuration, anonymized for the sensitive part, instructions here:

3

Hi

try to switch off autonegotation on Mikrotik's side. Set the speed manually to 10Gb and watch the results.

4

I don't think it is possible, unless something changed:

AND it is not documented:
https://help.mikrotik.com/docs/spaces/ROS/pages/220233794/MikroTik+wired+interface+compatibility#MikroTikwiredinterfacecompatibility-S+RJ10

the /r2 version added some features, but not manual speed settings.

5

Here’s the CRS305 config, it’s at factory defaults other than setting it as a DHCP client. I also have a USW Pro 24 that’s between gigs, so I can use its SFP+ ports to test this link, maybe get some additional data.

# 2026-04-12 05:12:40 by RouterOS 7.22.1
# software id = *
#
# model = CRS305-1G-4S+
# serial number = *
/interface bridge
add admin-mac=* auto-mac=no comment=defconf name=bridge
/interface list
add name=WAN
add name=LAN
/interface bridge port
add bridge=bridge comment=defconf interface=ether1
add bridge=bridge comment=defconf interface=sfp-sfpplus1
add bridge=bridge comment=defconf interface=sfp-sfpplus2
add bridge=bridge comment=defconf interface=sfp-sfpplus3
add bridge=bridge comment=defconf interface=sfp-sfpplus4
/interface list member
add interface=ether1 list=WAN
add interface=sfp-sfpplus1 list=LAN
add interface=sfp-sfpplus2 list=LAN
add interface=sfp-sfpplus3 list=LAN
add interface=sfp-sfpplus4 list=LAN
/ip dhcp-client
add interface=bridge name=client1
/system clock
set time-zone-name=America/Chicago
6

Dropping in the USW Pro 24 gave me one very important piece of information: I have a bad fiber. So I’ve ordered another cable, and will re-test with that one. MikroTik support doesn’t have an answer for why the CRS305 isn’t getting a link on the S+RJ10, but they did point out that the 10GTek bridge doesn’t appear to support autonegotiation (it’s 10Gb only), so that might be why the S+RJ10 didn’t work with that hardware. I’ve also ordered another H!Fiber 10Gb copper module, so I can see what happens with those on both ends of the Cat5e run. Once I get good fiber in place (sheesh), the 10GTek might end up working after all.

7

Hey, whattaya know, using a good fiber pair makes a big difference. Amazing. :face_with_spiral_eyes:

I no longer need the CRS305 so will be returning it, very lightly used. I did gather some interesting datapoints, though, by comparing throughput across the shielded Cat5e run using various combinations of hardware. I first used my spare USW as a fiber-to-copper bridge, then swapped in the 10GTek bridge, and ran a half dozen default iperf3 sequences in each configuration:

USW-USW + 2 MikroTik S+RJ10: 2.01-2.03 Gbps
USW-USW + 1 MikroTik / 1 H!Fiber ASF-10G-T : 3.2-3.5 Gbps
USW-USW + 2 H!Fiber: 3.43-3.68 Gbps
10GTek-USW + 2 H!Fiber: 3.75-3.95 Gbps

It’s interesting to me that the 10GTek bridge has higher throughput than the Ubiquiti USW, but even more interesting that the H!Fiber modules give almost double the throughput of the MikroTik modules. This doesn’t say anything about longevity, of course, because both copper modules run obscenely hot. But…if you want maximum throughput over a questionable cable, the H!Fiber ASF-10G-T might be a better choice than the MikroTik S+RJ10.