Someone in our end said Cambium stated that these could be propagated from the wireless, out of sync, noise, collisions etc. The FCS seem to increase if SM's are running high loads of traffic.
If this is true, how can this be propagated down the cable to the switch? The wireless interface, or at least the ethernet port on the radio, should discard this, according to standards.
Are Cambium using some other features that is the reason this might happen?
What is the bridging method used? Is there any method used that does not check CRC fields in the packet? Still, ethernet card on AP should drop the packet once it reaches the ethernet card, and not transmit it down to the switch.
I'm not sure who told someone that wireless issues could cause FCS errors on Ethernet but they were mistaken. The wireless mac has checksum protection so we will not forward errored packets from the wireless side into the software bridge. Furthermore, there is a retransmission mechanism so any errored parts of any packets are retransmitted and once a full clean packet is recieved, only then is it given to software for handling.
If you are using features like VLAN or NAT, in those cases, the packets are modified necessarily by the software either to insert/remove VLAN tags and/or modify the packet for NAT handling. In those cases, the SM will add a new CRC onto the packet as it leaves the Ethernet, but that also wouldn't result in an FCS error. The worst case there is if we have a bug and some bad data in the packet, it would be part of the FCS.
What kind of hardware are you using and is there any way that you could capture a packet capture with wireshark showing the packets that are having FCS errors by any chance? We may need to engage support directly with you for this to help you investigate offline and then report back here with any findings.
The issue was on a Mikrotik CCR 1009. We replaced that today, with an older model, Mikrotik 1100 AHx2 and so far we have no problems.
I do think we may see this problem on other sites with CCR's, so i can talk to the guys about getting a pcap file, but so far, knock on wood, it looks like a mikrotik ccr issue.
I think we will monitor this site for some time at first, and if the problems looks to have been fixed, we might try it again on some other site to verify if it is a Mikrotik issue or not.
Antoher theory i noticed written in the mikrotik forum, coming from a mikrotik "trainer" was that some professional systems could create "noise" in the wireless radio, that directly affected the ethernet card in the AP. This sounds at least theoretical possible, and it could also explain increase in FCS with increase of traffic, as the AP would be more busy. Suggested solution was to reduce power.
I would find that unlikely, but in the past I have heard issues depending on the length of cable and whether it is shielded or not. This is usually when it is a very long run up a transmission tower. At a customer site on a house for example, it seems it would be unlikely but not impossible. Shielded cable would be best but that can be expensive for using at every site. To be clear though, the interference that could cause such thing wouldnt be coming from the Canopy radio but rather from something else. There have also been some reports of inline surge supressors inducing CRC errors.
Another option is to change the Ethernet speed depending on the service speed you are offering, but these days it is very unikely that running the Ethernet at 10F would be sufficient.