Troubleshooting slow download speed

Unanswered Question
Mar 30th, 2010

Hi All,

Our network uses a edge router (3845)à firewall (ASA 5510) à two L3 Switches (3750) à Aggregate closet switches (3750) à access switches. (3560).

We are connected to our ISP with a DS3 line, and use VLANs for our inside network.

The problem we are having is low download speeds on our inside VLAN connected devices. To test I put a machine on the outside (outside address) on the same distribution switch as the edge router. My download speeds on the outside VLAN were a little over 20 Mbps ( In contrast, my download speeds on my internal VLANs (on the same distribution switch) dropped down to 2 to 3 Mbps. I tried various VLANs on the inside and they were all about the same.

I am monitoring bandwidth utilization % on the L3 Switch Gbps interfaces and they are all fractional. Could it be the virtual interfaces on the L3 switches that are the bottleneck? How would I test the bandwidth utilization if that was the case?

I will attach some screenshot attachments (.doc) of what SolarWinds is showing.

I just tested my my 'Outside' VLAN on a switch in my office, and the download speeds were again about 24 Mbps. I then connected to our staff VLAN on the same switch and it dropped down to 1.5 Mbps.

I have this problem too.
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Michel Hegeraat Tue, 03/30/2010 - 23:22

Do you have any idea how traffic flows throught your network? From your pc to the internet and from internet to your pc. Its not always the same!

Draw  a physical and a logical schema.

Next check every link the traffic goes through when you are in the "staff" vlan, except the ones that you alse use when you are in the "outside" vlan.

Yhese later ones are apparently OK.

Also you may want to check with a tool like wireshark if your download traffic contains retransmissions when you are in the "staff" vlan.




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