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CRC errors on Switch Ports

By Bert Bolin ·
I have a Cisco 2621 Router with 2
Ethernet interfaces that connect via a
patch panel to a Cisco 2900XL switch.
The router displays no errors on the
Ethernet interfaces yet the Switch ports
are incrementing input CRC errors on the
ports that talk to the router. I have tried
different cables, and different ports on the
switch and on the patch panel. I have
also verified that the contention is set for
100 Mb/Full Duplex on both sides and it is
linking up correctly.

I have contacted Cisco but the call is
lingering and so far what has been done
at their suggestion has not helped
(disabling TCP keepalives). I am sure
that the cables and patch panel
connectors, etc. are all in good shape
and I have tested them clean with other
Full Duplex devices.

Any clues on what this might be caused
by, where to look?

Thanks

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CRC errors on Switch Ports

by -Q-240248 In reply to CRC errors on Switch Port ...

A high number of CRC errors from a signal station usually indicates a faulty router ethernet port or corrupted software drivers (Cisco IOS) or a bad cable connecting the station to the network. If the errors are associated with many stations it is bad cabling, router ethernet port, hub port or induced noise in the cable system.

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CRC errors on Switch Ports

by Bert Bolin In reply to CRC errors on Switch Port ...

This is good general information but
all these indicators have been
accounted for.

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CRC errors on Switch Ports

by richard_woo In reply to CRC errors on Switch Port ...

Try running with the half-duplex first. Cisco devices are known to have problem running on full-duplex mode.

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CRC errors on Switch Ports

by Bert Bolin In reply to CRC errors on Switch Port ...

This was an interesting answer and I
gave it a shot. It didn't make an
impact though. I am glad in a way
that it didn't because the Cisco
products are expensive and certainly
should be able to do Full Duplex
error free. So my quest continues...

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CRC errors on Switch Ports

by darra In reply to CRC errors on Switch Port ...

If you have eliminated any possiblity of a physical layer problem then the only viable remaining solution is duplex and speed. Make sure neither side is auto-negotiating. If this is a true statement then back the speed to 10 full duplex and see if errors decrease.
Another slim possibility is extreme congestion. Keep an eye on when the errors seem to rise the most.... and compare to loads at that time.

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CRC errors on Switch Ports

by darra In reply to CRC errors on Switch Port ...

One other important lesson I learned the hard way...replace the cable between the two devices. Cables are cheap and are more often the problem than anything else.

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CRC errors on Switch Ports

by Bert Bolin In reply to CRC errors on Switch Port ...

Excellent answer. Unfortunately all
this has been accounted for. Load is
well within acceptable ranges, CPU
ultiization is normal, no sign of
working the switch too hard or the
router for that matter. The ports were
using autonegotiation andI did try
manually configuring them for Full
Duplex 100 MB and this did not solve the
issue. I will try setting the
contention to half-duplex to see if this
will resolve the issue.

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CRC errors on Switch Ports

by rwscc In reply to CRC errors on Switch Port ...

I assume you have tested the cable to cat5 specs for attenuation, noise, and crosstalk. Even if the cable passes with flying colors, you could get noise betwwen the router and switch ports. Check the ground connections on both pieces of equipment. Ihad a bad ground between two outlets on the same powerstrip before (admittedly a cheap one.) If there is too much resistance in the ground path between the two devices, there will be a voltage diference that varies with the ground current. A mild grouinding problem can cause CRC errors, and a major grounding problem can damage the port circuitry or the entir device. From what I see you've already tested everyting else.

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CRC errors on Switch Ports

by Bert Bolin In reply to CRC errors on Switch Port ...

The question was auto-closed by TechRepublic

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CRC errors on Switch Ports

just a suggestion (besides the grounding and bonding suggestion, which you should check with installation anyways) is the IOS,
Were you experiencing these CRC errors with the older IOS's? do you have another router that you may be able to switch the Flash and RAM with? it may be the most pain in the butt thing to try, but better than massive congestion if the errors increase (and the retransmits increase)
Good Luck.

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