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Network troubleshooting help? 1

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hinesjrh

MIS
Jan 4, 2005
260
US
I have a group of HP 2950 switches at a remote location, set up in a stack. The primary switch (commander) is showing "Excessive CRC/Alignment" and "Excessive Late Collisions" on port 1. Connected to port 1 is the Cisco 2610 router that connects this remote site to our WAN. I see on the internal (Ethernet) interface on the router that there are Input and CRC errors.

Users are this remote site are complaining about slow access to everything (apps. and files on the server, access to the Internet, etc.). What could be causing these errors?

The external (serial) interface on the router is and stays clean. The other switches in the stack are pretty clean as well (little or no errors).

Could it be as simple as the cable between the router and the commander switch?

If I had a client or NIC on the network there causing extraordinary amounts of traffic, what would that look like? How can I get to the bottom of this?
 
Late collisions are often a sign of duplex mismatch. If the HP thinks the connection is half duplex, and the Cisco thinks it is full duplex, then when the Cisco sends packets while the HP is already sending, they will be interpeted as late collisions.

Half Duplex, the link can send OR receive

Full Duplex, the link can send AND receive

Autonegotiate, the link tries to automatically determine speed and duplex, but it is only 99% sucsessfull. a 'feature' of Autonegotiate is that it only works with other Autonegotiate ports or ports set to Half Duplex, but NOT ports set to Full Duplex.

I would first check the Cisco to be sure it is in fact hard coded to Full Duplex. If so, we are on the right track, next check the HP, if it is set to either Autonegotiate or Half Duplex, then we know the trouble. Try setting both devices to Full Duplex, if that cures it, great, if not, set both devices to Half Duplex. Duplex mismatch would also explain horrible throughput. (There is a FAQ on this in this Forum)

If it is not a duplex problem, is there any chance the link between the HP and the Cisco is REALLY long? It would take quite a delay to get Late Collisions just due to the speed of light. Can the cable link be replaced easily? CRC errors often are the result of bad wiring or bad electronics, and wire is cheaper than electronics, so start there.




I tried to remain child-like, all I acheived was childish.
 
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