Switch 3750 causing CRC errors on router WIC

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Nov 3rd, 2009
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Dear all,

Does someone has already encountered the following ?

I have two routers CISCO2851 linked by microwave with E1 interface (VWIC2-2MFT-G703). I have too much CRC errors on both E1 interfaces when one of the routers is connected to LAN switch.

But if I cross connect a PC directly to the LAN port, no error occurs even if I load high traffic.


Is it possible that a LAN congestion on the switch could cause CRC errors on my E1 WAN interfaces ??

Some colleagues think that the switch might have an electrical problem passing electrical flow through the Ethernet copper cable, and cause router clocking unstable.


Any help is much appreciated.


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aaberdeen Wed, 11/04/2009 - 08:45
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i think this is expected connection from the outside world hits router cisco02851 and communicates to R2(cisco02851)if there is a LANswitch or L2 switch connectd to a PC then there is a TCP hanshake in place.


Router1 -------------- Router2

(microwavelink)

this will be bouncing between the 2 E1 interface.Hence you will have CRC error..#


Router1 -------------------- Router2

! (microwavelink) !

! !

LANswitch/L2_________________LANswitch/L2

^ (ethernet/gig connection) ^

^ ^

^ ^

PCS PCS

with the PCs(workstation)in place as the final recepient there is a TCP ack/handshake and windowing in place.we have to bear in mind microwave links are always constant.


you can run a protocal analyser(wireshark) on one of the interface and watch trends

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