Slow CIFS over WAN

[Devavrat Oka]

This is a multi site network. Site A has a Cisco 3825 router and connects to 3 other sites over ISP A and 2 other sites over ISP B. Both ISP A & B provide a layer 2 full mesh network. ISP A provides a 100mb pipe while ISP B provides a 20mb pipe.

File transfers (Windows - CIFS) over ISP A's fiber are fast enough and throughput is good. However, file transfers (Windows - CIFS) over ISP B's fiber are slow, even though latency is good.

On the 100MB ISP A pipe, file transfer speeds upto 6 MBps are achieved. On the ISP B 20MB pipe, speeds upto 300KBps are seen for file transfers.

ISP A connects to an on board gig port on the 3825. ISP B connects to a fastethernet port on an HWIC-2FE card on the same 3825. Both ports then connect to ISP Switches and then full meshed to remote site Cisco routers.

What could be the issue? Why am I facing these issues only with ISP B even though the configs for ISP A and ISP B are the same?

Thank you.

[Jeff Van Houten]

I've had similar experiences in the past. A few things to investigate.

1. Any errors on the link? Large packet ping tests failing? Cifs and ms don't always work well with an MTu other than 1500, especially if it is the "middle" of a link. Do ping tests and make sure you MTu is set properly. After you determine MTu, set mss as well.

2. Same as above, but error more random? Have service provider verify all individual circuits in the path. On two different circuits I've seen bad or misconfigured equipment in the providers network cause the symptom you see. Have them look especially for a duplex mismatch somewhere.

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