On my company's LAN, we are experiencing low upload bandwidth. Download bandwidth is fine. We have a 10 Mbps up and down through our ISP, but the upload has been around 1 Mbps (download around 9.7). This is consistent throughout the entire day. I noticed this trend about a week ago. The only service we use that would affect this would be carbonite backups, but we only use carbonite for a hand full of files, and we've used it for years with no issues.

For a quick and dirty description, we have Netscreen firewall, with a web server, database server, and isa firewall client server behind it. Behind ISA, we have our domain controllers, staff computers, etc. We also have a SAN environment with a dedicated vLAN I installed a few month ago.

  • I ruled out ISA as the problem by bypassing it to test bandwidth.
  • I checked bandwidth usage on all devices, and I do not see any issues.
  • I disconnected everything behind ISA, and nothing changed.

The ISP says we are only using about 30% of our upload bandwidth, with spikes near 100% for a brief period during the morning hours.

Could this be a physical layer problem? What are some avenues I should inspect next? I'm wondering if it's possible to have a bad router.

  • First thing I would check is to disable auto-negotiation on your switch ports that connect to your ISP provided router/modem. Set them to 100mbs full. Also, what are you using to test bandwidth? A single file transfer or multiple transfers from many address (such as a torrent) – Bert Jun 26 '14 at 15:28
  • Plug a workstation or laptop in as close to the router as you can get. If you can plug directly into the router that's best. You may need to reconfigure your workstation/laptop ip address. Then test your upload speed. If it's the same then you've ruled everything out except for the router and the connection. You can then troubleshoot it with the ISP. If the upload test is OK then start working your way inward/backward from there. – joeqwerty Jun 26 '14 at 15:36
  • Thanks for your comment, Bert. I've been using speedtest.net to check the available bandwidth. I use PRTG Network Monitor to track the data going in and out, looking for red flags. Using resource monitor, Network Utilization hovers around 0% with spikes to 25% at times. – Josh_with_questions Jun 26 '14 at 15:37
  • Thank you, joewerty. I did try that, and the bandwidth remained unchanged. I was wondering if this could also indicate a bottleneck somewhere. – Josh_with_questions Jun 26 '14 at 15:39
  • Did you plug your laptop directly in to your connection and make sure you are provisioned correctly? Definitely do this after hours. – David Eisen Jun 27 '14 at 2:50

Well after trying all of your great suggestions, I called our ISP again to have them look into the problem. It turns out there was an issue within the handoff to another ISP. The cable has been replaced, and all is well now.

Thank you for the help!


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