FEC, CRC, HEC errors

[C69nc3R]

When it comes to router issues what are FEC, CRC, HEC errors? And how do i fix them?

[reaper]

when you send a frame, you compute a CRC, which means you take the data as input and produce a "unique" output.  when the frame arrives at the next router, it computes the CRC of the frame, and if doesn't match, the data is corrupted and the frame disgarded.

you need to check layer2 configuration, for example, making sure you have the correct duplex in ethernet, if so you're looking at the physical layer, perhaps a bad cable or failing interface.  the latter being the most likely problem as it's a symptom of a physical layer problem.

fyi, typically ethernet is used over copper cat5x cable.  there's twists in the cable which cancel out electro magnetic fields.  since you really only use two pairs, the two pairs are actually set further apart physically, although straight thru is straight thru, it could be wired weird.  what type of medium and networking are you using? is it a manufactured cable?

[QwazyWabbit]

FEC = Forward Error Correction
CRC = Cyclic Redundancy Check
HEC = Header Error Control

These are all related to validating the integrity of the communications channel in use. These can be primarily ISO Layer 2 errors or in some protocols, layer 1 or layer 3.

It means the router is having trouble communicating. There is a bad cable, electromagnetic interference or a hardware fault in the router or whatever it is communicating with.

Check cables, power supplies, replace the router, check whatever is communicating with the router.

[reaper]

I would try a known good cable and different interface or router.  Is this wired ethernet?  If so you probably have a bad cable.  Just use one that's working : ).  When the router gets the frame and it can't double check the CRC, the data isn't good, and is dropped.  Then TCP will have to take care of things and retransmit, or you see a red line for Q2, since Q2 uses UDP and the application doesn't care because the data is so time sensitive.

For the error checking it's at layer2 and up, and to be removed from layer3, where layer4 will verify reliable end to end transmission with TCP.  Layer2 is responsible for error correction, whether it's ethernet, ATM, POS.  The physical layer includes electronic components.  These components genreally depend on timing at well below microsecond intervals, and they do not correct errors.  At least that's how the common networking protocols appear on wikipedia relating to the OSI model.

The OSI model is about passing PDUs (protocol data units) up and down a stack to have a modular framework, to make NIC cards interoperate easily with NDIS, to pass data between different mediums reliably.  It's not an exact science but has made everything work, and is certain good for troubleshooting.  Like if you ping without loss, so no point in worrying about layer2.  The top layers sessions,presentation, and application haven't been followed according to the RFCs, so the TCP model was made, which is the same but groups them all as application.

[C69nc3R]

It is wired. I have tried different cables and still get errors. may be the router itself

[reaper]

What interface increments CRC errors?  Do you have a switch?  When you swapped the cable did you get a green LED lit on both ends?  If so try different interfaces or a PC with another NIC.  Also make sure both ends are set as auto-negotiate.  A router to PC you may need a crossover cable to to hit some type of button that says auto-mdix or uplink.

[VaeVictis]

What interface increments CRC errors?  Do you have a switch?  When you swapped the cable did you get a green LED lit on both ends?  If so try different interfaces or a PC with another NIC.  Also make sure both ends are set as auto-negotiate.  A router to PC you may need a crossover cable to to hit some type of button that says auto-mdix or uplink.

router ports to clients do require a cross over just clarifying... however, if he is plugging into one of the normal soho routers, those contain switch ports not router ports so he probably needs a patch

[reaper]

router ports to clients do require a cross over  just clarifying... however, if he is plugging into one of the normal soho routers, those contain switch ports not router ports so he probably needs a patch

I think you're right he needs a straight thru cable to connect to the switchports on the router.  however having to use crossover or straight thru cables is going away because of auto-mdix.  you will just always use straight-thru, and router to PC is a crossover cable:

a router to PC is a crossover cable (termed loosely DTE to DTE, because they don't generate clock signals and are end point devices), because you won't be internally switched, in other words transmit will talk to transmit and you won't have an ethernet link.  the soho routers may be different because they have an internal switch expecting to be connected to a PC, except for the WAN port (and something like a 4 port switch), but as a general rule a router terminates the connection and will not talk to a PC without a crossover cable.

the type of cable depends on if the interface is switched internally or not, in other words the conductor tip (+) talks to conduction ring (-) from the transmit pair to the receive pair.  auto-mdix takes care of transmit talking to receive, but before auto-mdix  you needed to hit the little button or use the right cable.  the IEEE also recommends auto-negotiate to auto-negotiate, because ethernet doesn't automatically detect duplex, and configuration errors occur.  it's a long standing myth that you need to fix the speed and duplex in ethernet, which may be true for some older devices.