I have a CRS125-24G switch/router running 6.19. When I connect it to a STX radio via about 150 feet of shielded, CAT6 cable, the port keeps going up and down. It will sometimes stop flapping if it negotiates 10 Mbit/sec. If I plug the same cable into another dumb switch (Netgear or DLink) (or into a port on a RB2011UAS router that was previously in use) it successfully negotiates 100 Mbits and stays up. If I then plug the Netgear or DLink switch into the same port on the CRS125 (so the Netgear or DLink in in the path) I'm able to talk successfully to the STX and the CRS negotiates a 1Gbit connection with the Netgear or DLink. This happens for any of the ports on the CRS125.

Why won't the CRS125 negotiate a 100 Mbit link with the STX radio?

I've tested the cable with a cable tester and all the pairs test OK including the shield.

Bump. Anyone else see this problem?

try forcing the port to 100Mb/s. Or perhaps you can plug it into a switch which plugs into the CRS.

try forcing the port to 100Mb/s. Or perhaps you can plug it into a switch which plugs into the CRS.

It does not help to lock the port to 100 Mbit/sec. It still flaps. As I mentioned above when I plug it into a switch which plugs into the CRS, it works. (The port to the CRS runs a 1 Gbit, and the port to the STX runs at 100 Mbit with no flapping.) But this all seems to point to some deficiency in the switch chip in the CRS, right?

I have an identical setup.

CRS125-24G connected to a SXT Lite5.

What ever port the SXT's PoE injector is plugged into continually goes up and down.

An added piece of information is that the SXT has the following error in the log: Which is weird, cause all that the SXT is connected to via its wireless interface is another SXT where my cable modem is.

I have started talking to support, and we are at the point where I am ensuring that both the SXT and the CRS are grounded.

But similar to ddejager, I have put a small 8 port netgear switch in between the SXT and the CRS and I no longer see the port changing state.

When I had RSTP on for the bridge on the SXT this would result in an outage of a few seconds while the bridge sorted out what was going on. With it off, the drops aren't as noticeable, but they are still logged.

With the switch installed between the SXT and CRS there are no port transitions, and the strange bridge error doesn't occur.

On the other end of the SXT link I have a SXT Lite5 connected to a RB750GL and don't see any of the port transitions. I only see them when I connect the local SXT directly to the CRS.

Everything is running 6.29.1 (Firmware 3.22)

chris.

I ultimately replaced the cable between the SXT and the problem went away. The old cable tested fine with a cable tester, but seemed to cause port flapping.

I ultimately replaced the cable between the SXT and the problem went away. The old cable tested fine with a cable tester, but seemed to cause port flapping.

cable testers have a limited reliability

have you tried mikrotik Ethernet interface integrated cable test??

the cable testers many times test ok a faulty cable, do not trust them

I grounded my CRS and there was no change.

I was going to work on grounding the SXT, but decided to try and better understand why using a 2nd switch in between the CRS and the SXT caused things to work (and not report the problems).

If you reference the following picture.


You can see that the port (ether24) actually stayed "linked" even after I removed the connection to the SXT. This struck me as strange.

I then proceeded to unplug the power from the PoE injector and the link started to transition state very quickly.

The following videos display this quite well:
https://www.dropbox.com/s/2sz3vbd1izpir ... 2.MOV?dl=0
https://www.dropbox.com/s/nd19uku71gpov ... 5.MOV?dl=0

After seeing that I decided that something might be up with the PoE injector that came with the SXT. I happened to have the following sitting around:
http://www.adafruit.com/products/435

And after verifying the pinout with regards to the power pins I confirmed that it was compatible and swapped it into the setup.

Once I started using this PoE adapter I no longer encountered any issues with the CRS to SXT link. All the strange bridge errors stopped occurring and there were no longer any port flapping on the CRS.

I am chalking this up to a potentially defective PoE adapter that came with the SXT, and that the CRS didn't particularly like it.

At this point my setup is running well, and I think I have solved my issue.

Hopefully somebody else can benefit from this information.

chris.

I have same problem with 12 Cap 2n & CRS125-24G-RM. All APs connected to CRS125 By Dlink Cat5e SFTP Cable. (Grounding is OK)
Cables over 20M length has this Problem but shorter Cable working normally. when I use other Switch( Dlink 16port 10/100 Switch) or when I turned off the Ethernet Auto Negotiation and used only 10Mb/s speed instead of 100Mb/s (in advertise section) everything is Normal without any Port Flapping.

Hello,
This week I had the same problem. The scenario:
CRS125-24G-1S-RM, on port 24 is connected POE injector that powers SXT Lite5 over 50 meters cable.
The port is flapping on random intervals, most commonly in about a few seconds. We changed connectors on both sides, then changed the POE injector (both is new and original MikroTik), changed the port of the switch... Then, changed the whole cable, still nothing. Tried forcing on 10 mbps/half duplex... Stops flapping, but still no useful data over the port.
Another strange thing is that the Switch port flaps MORE than the port on the SXT. I connect to it over the wireless link, and monitor both side by side...
I "resolved" the problem by putting a "dumb" switch between the CRS and the SXT and now anything is fine... but WHY THE HELL?

I would like to receive meaningful answer from the support, Why I have to spent 3 days trouble shooting new deployment?
What is the problem with this CRSes ? And how to fix it the professional way, not putting another device in-between ?

P.S.: Please move the topic to the correct board.

Zetle and others,

we had similar problems with many SXTLite5 units, ethport randomly flapping against devices from other manufactures (Netis, Zyxel, Asus...)

After some longer time with trying almost everything (replacing SXTs, other devices, cables etc), we have found, that this problem is casued by PoE Injector (original from Mikrotik) which is included in box with SXTLite5.
Some combinations of this PoE injector with specific cable lengths (don't remember exactly at which lenghts it started and stopped) and SXTLite5 caused ethport randomly flapping.

We have exchanged PoE Injector for different type (Gigabit type from Mikrotik or Injector from other manuacturer) and everything started working, eth port stopped flapping.

Problem was only with PoE Injector and SXTLite5, if same injector used to power other device, there was no problem.

So if you have problems with eth flapping over PoE, try replace supplied PoE injector for completely differrent type (Mikrotik Gigabit PoE Injector (white with LED), or other manufacturer (we use Ubiquity PoE) works fine.

@zichovsky: Thanks for the replay... I asked MT support by mail, and their conclusion was, quoting: "Please consider grounding these devices as it currently seems the cause. Janis"
After more research I tried replacing the PoE injector with other one (Purchased from AliExpress for $1.40) and it works fine.

So, the bottom line:
Mikrotik's PoE injectors included with SXT and probably other devices not working correctly with CRS125 with cable longer than ~40 meters, but works fine with other devices, including other Non-CRS Mikrotik devices or just "dumb" switches.

Port Flapping on CRS125 when using RB Metal 2SHPn:

After a year and half of having this problem and using a generic network switch in between to stop the incessant port flapping, I may have our solution, Gentlemen! I had an incessant problem of a port flap every 30 seconds when connecting an RB Metal 2SHPn to the CRS-125-24G using the PoE directly at any port in the CRS-125. All systems are grounded. Temporary solution was to use a generic network switch in between the RB Metal and the CRS-125. I've awaited 18 months for a firmware update or a reply back from Mikrotik about this issue, but nothing has come. I finally found how to fix this error!!

I did not try zetle's solution. I have a duplicate RB Metal 2SHPn that I took out of the box one day. I noticed that when I plugged the duplicate RB Metal 2SHPn into another network jack in the same building connected to the same CRS-125-24G, there was no port flap. I used the PoE injector at the network jack in the building, instead. There wasn't a single port flap in three days. This said network jack was about 30 feet (10 meters) from the network switch. So, it appears that the PoE injector cannot be very close to the CRS-125 at all. I did try using direct D.C instead of a power supply, but still received port flaps when using PoE injector at the CRS-125. The distance is the key. I made a pig tail about 30 feet (10 meters) (male and female jack on the other end) that I needed for a lead dress anyway to the exit location. I now have the PoE injector going into the female just before the exit to the outside of the building 30 feet (10 meters) from the CRS-125 and there hasn't been a port flap in a week.

If Mikrotik is reading this thread, can they investigate why the PoE injector has to be a distance from the CRS-125 and cannot be directly plugged into the unit? As I've said, I thought it could be a noise issue from the power supply, but even when using battery D.C, the port flap still exists when PoE is directly plugged in to the CRS-125.

Thank you for this thread, Gentlemen. I am glad to see that I'm not the only one who had this problem. It was driving me insane. I hope this works as a solution for now and Mikrotik can investigate their PoE injectors.

The problem appear with longer cables. We have setups with CRS and hAP as Access Points powered over PoE injectors on short length cables and it works OK.
Another solution is to use third party PoE injectors. I currently use one from eBay, that cost $1.5 and works fine with long cables and CRS. Here I'm talking about 100mbps links. Not tested on 1 gbps, but probably with ubiqty or similar poe injectors it will be fine... Still CRS is a buggy device, not suitable for serious work but perfect for all-in-one solution for small offices.