6500 overruns and "too many retransmissions"

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Oct 23rd, 2007
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After putting a sniffer on the network, we noticed a significant number (900+ in less than 5 minutes) of diagnoses with the message "Too many retransmissions". Even if we bump the threshold up from the default of 10% up to 50%, we are still seeing a good amount.

In general, the retransmissions are going from host workstations to the server farm (Exchange, intranet, and file servers). They occur throughout normal business hours.

From the core switch where the servers are connected, we notice that they are all connected to a WS-X6548-GE-TX module. The port counters show overruns. One would think that the overruns are directly related to the retransmissions, right? However, the counter only increments during off-hours (when backups are running).

The 6500's cpu and memory are not overly taxed. What other counters can I look at to determine if these retransmissions are related to the performance of the 6548 module during normal business hours?

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szahid Tue, 10/23/2007 - 14:48
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You should specifically look at

show counters interface

and look for OutDisacrds / qos3outLost counters. This card is 8:1 oversubscribed which means 8 front panel ports connect to a backend asic through 1 Gig connection. Other counters you should look for is flowcontrol. Is the interface being flowcontrolled as well ?

show interface flowcontrol will show you that info.



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