Hello guru's!

I've got my 10G setup with core switch as CRS305-1G-4S+ (sw1) and delivery switch as CSS610-8G-2S+ (sw2) with cat 6e (<15m) connected with SFP+ S+RJ10 (Cabinet link). I'm using VLANs, as seen in screenshots. Core switch have ONU uplink to internet provider, and connected to 10G NAS and core router.

Well, it's target configuration, and I can't make it work properly. At sw2 I have Port 8 and SFP+1 as identical setup, as seen on screens. When sw1 connected to sw2 via Port8 (1G), it works perfect. When I move connection to SFP+1 (10G), I've got immediately "connection lost" with both switches. I'm sure all hardware and cables are good, seems like it have some wrong settings.

Please help me find where I am wrong? How to get them connected with 10G link?

Is this forum dead? Any ideas how to fix or debug?

Well, a few screenshosts is a hard challenge to fully understand your configuration on devices. It could be trouble with STP, but who knows. ICMP is working on switches? Switching still works or even traffic is stopped?

SwitchOS is easy to configure, but RouterOS gives you logs - debug. I would recommend to switch to RoS on CRS and make same configuration, if trouble repeats, you can see details in logs.

I would recommend to switch to RoS on CRS and make same configuration, if trouble repeats, you can see details in logs.

Well, even your post doesn't contain solution, it really helps me to go deeper, thank you!

I has reboot crs305 to RouterOS and set it up as the same as SwOS, connect PC for each switch, and found flapped link between switches Logging doesn't help too much, it just link up / link down every ~2 sec. I've tried replace ports from both sides, replace SFP's, no any difference found. I'll try later to replace RJ45 later from one side to be sure it's not a reason. Internal "cable test" doesn't help - it shows flapping link ok/ no link. When i change port to 1G at CSS10, i have stable link with up to 900 Mbps throughput according to speedtest.

Really strange fact is, even i set port negotiation to 1G, 100M or 10M, it doesn't stop port flapping! My cable is thick ~10m long STP CAT 6e in-wall with heavy duty field connectors both side.

What can be wrong with cable (or not?) with such strange effect?

Well, for 10G I use only optic or DAC, I don't have any experience in real life. However, for testing, CAT5e is capable to link with 10G, so you can make quick test if trouble is in HW or wiring.

I recommend TDR measurement of cabland you will get precise answer

Well, i fixed it by replacing Mikrotik's pair SFP by some Chinese local brand EECX SFP-10G-T bought from Aliexpress. My hope was I will have at least 5Gbs, as far as Mikrotik's SFP+ doesn't allow to lock lower speed, but these are promised to use 5, 2.5 or 1 Gbps.

But I got full 10Gbs on same cable! And more, it keeps temperature about 52 under under full load with iperf3! My S+RJ10 was heating up to 120C (!) in CRS305-1G-4S+ before I put external fun and heatsink. May be temperature shows incorrect, but it doesn't burn fingers.

- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bandwidth Retr
[ 4] 0.00-10.00 sec 3.26 GBytes 2.80 Gbits/sec 21 sender
[ 4] 0.00-10.00 sec 3.25 GBytes 2.80 Gbits/sec receiver
[ 6] 0.00-10.00 sec 2.52 GBytes 2.17 Gbits/sec 0 sender
[ 6] 0.00-10.00 sec 2.51 GBytes 2.16 Gbits/sec receiver
[ 8] 0.00-10.00 sec 2.55 GBytes 2.19 Gbits/sec 0 sender
[ 8] 0.00-10.00 sec 2.54 GBytes 2.18 Gbits/sec receiver
[ 10] 0.00-10.00 sec 3.23 GBytes 2.78 Gbits/sec 0 sender
[ 10] 0.00-10.00 sec 3.22 GBytes 2.77 Gbits/sec receiver
[SUM] 0.00-10.00 sec 11.6 GBytes 9.93 Gbits/sec 21 sender
[SUM] 0.00-10.00 sec 11.5 GBytes 9.90 Gbits/sec receiver

iperf Done.

Thanks for your advises!

Interesting on the Chinese SFPs. I am also using non-Mikrotik 10G optical SFPs in my CSS326 switches, and they are working great - and were A LOT less expensive then the Mikrotik SFPs. It is well known that the electrical SFPs get hot. I think that the 10G optical SFPs are running cooler than the 1G electrical SFPs.
These are the ones I'm using: https://www.amazon.com/gp/product/B01LY ... =UTF8&th=1

Same experience here: some chinese SFP 10GT just don´t work, but some others are much better& cheaper than the MT SFP 10GTs.
I would add, that wherever I can I use DACs or optical MM 10G interfaces. They are cheaper , use less power and make less troubles than 10G-T.
I have the same combo CRS305+CSS610 interconnected by a DAC. It always worked.