Yesterday (the same as before about 3/4 year) to WAN IFC CCR appeared on "FCS Error on interface" error. At that time we thought it was a fault mikrotik and did not pay it much attention.

IFC could turn and errors disappeared.
But this morning it appeared again and turning the IFC, it decides not solved During the 15 minutes it was so 1260 RX FCS Error statistics IFC.
Thus, unlike the day before yesterday against a "Back then" was that the IFC normally ping and communication over IP function (the question of how long it would take).

What we tried:
1) gradually turn off IP addresses in an attempt to isolate the communications that fall - without success, they doing it all
4) disable IFC and after a while switch on - no Results

Finally, in this case helped disable all addresses in Adress list and gradually one by one turn on, turn off, then turn the other one on and off, to turn each of them has always been for a while primary address, at that moment dana address is always started from the outside Ping this style we all eventually turned and began to work, but not a solution.

Yesterday, on the recommendation of the man in our housing turn off Auto negotiation on an Ethernet port, and set to fix 100Mbit full duplex.
When I turned on him again today (auto negotiation) and FCS Error disappeared (according to IFC well log set 100Mbit Fullduplex)
So I think it's some kind error somewhere ...
Technic guy said he had also solved it with Mikrotik and that was just a problem in that the IFC runs at 100Mbit - which is the only difference from previos housing (there was 1Gbit O2 is 100 Mbps per line)
Netwatch meanwhile is set to GW and if there is a timeout 5s (once per minute), and it turns IFC WAN (it solves unavailability), but does not generally FCS Error.

So if it happens again, there will be an interesting test by me throw it on the RB2011 or whatever it is, because he has a physical 100Mbit interfaces. Optionally upgrade from 100Mbit to 1Gbit (which is unnecessary, peak traffic was 35Mbit)
I must say that on the other (admin router - the RB2011) it has not happened yet not once - there is a 100Mbit link, so maybe it's best estimate

What do you think?

log:
...
xxxx interface,warning ether1 - WAN fcs
error on link
xxx interface,warning ether1 -
WAN fcs error on linkxxxx interface,warning
ether1 - WAN fcs error on linkxxxx
interface,warning ether1 - WAN fcs error on link
xxxx
xxx interface,warning ether1 - WAN fcs error on linkxxxx interface,warning ether1 - WAN fcs error
on link
...

FCS errors usually indicate L1/L2 problems.

Disabling autonegotiation is always an (ugly) workaround and will lead to other issues in the future; additionally it will just mask the issue.

Question is: why after 3/4 year, with no other setup changes, this started to happen?

I would try different cable/fiber pigtail, different ether port or SFP module, a different IFC...

Hi,

I have a two CCR1036 each with wan interface connected to unknown Cisco switch. Only those wan ports were seding "rx fcs error". It is not problem related to cat6 cable or ethernet port self. When I disable autonegotiation I receive more rx fcs errors. It seems that combination of autonegotiation enabled and rx/tx flow control enabled don't generated those errors.

It is strange forums ale full of ideas that fcs errors are related to Mikrotik CCR series only, especialy when Mikrotik implement flow control on ethernet.