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WAN File Copies - slower 1 direction

We have a 150MB TLS type circuit between our 2 main sites, connected to GB fiber ports on each end via Cat6509. File copies between servers with GB LAN connections 1 direction are fast (3 seconds for a 20MB file) but can take as long as 90 seconds the other way for the same 20MB file.

Flow control is enabled on the link and we do see RX Pauses incrementing, and we see retransmits occuring in the slow direction. It is not server specific and we have shown that local copies work fine.

The carrier has certified the WAN link as healthy and we are struggling with where to look next. Any suggestions?

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Re: WAN File Copies - slower 1 direction

If you are getting RX pauses incrementing then that means that from the switch port perspective the device you are driving cannot keep up wih the amount of traffic flow to it. So it sends to you RX pauses to try to invoke Flow Control to it. If both devices (switch port and server or end device) are Flow control enabled then Flow control will be invoked . If any of these devices are not flow control enabled or capable of running flow control then you can potentially have drops on the flow. Verify that flow control is enabled in both directions and also that the server and end devices are flow control enabled. If your 6509 is CatOS then do a SHOW COUNT xx/yy command to see all errors on the port (You may want to clear the counters). If it is an IOS based switch then do a SHOW INTERFACE GIGxx/yy and see if you are dropping any data on the Input and Output queues....Good Luck...

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