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Brent
Asked: 2010-10-05 12:31:50 +0800 CST

Small TCP Window on WAN between 2 Locations

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Site A: Denver datacenter. 60MBPS.
Site B: Chicago. 100MBPS.

ICMP pings:
Packets: Sent = 176, Received = 176, Lost = 0 (0% loss), Approximate round trip times in milli-seconds: Minimum = 74ms, Maximum = 94ms, Average = 75ms

File transfer between sites that never goes past ~7MBPS:

http://www.bunker7.com/images/xfer1.jpg

Windows Update download at 60MBPS+:

http://www.bunker7.com/images/xfer2.jpg

Site to site: IPSec VPN using two Cisco 5520's. CPU at 3-4% and lots of memory to spare.

The latency between to two sites is very acceptable so I can't see an issue why it is performing so slow when transferring between the two sites.

I have found that any type of transfer (FTP, HTTP, Windows file shares) will never go above ~7MBPS.

When the WAN was first setup, I was able to get transfers at 50-60MBPS, which is what is expected due to the WAN connection at the Site A at 60MBPS. Then a few days later, I was not able to get anything going faster than ~7MBPS.

Is there a upstream router between Denver and Chicago causing this? I want to take the blame away from our setup as downloads from Windows Update go blazing fast and for the first few days after the site to site VPN came up, I was transferring VM images at 50-60MBPS.

Our stack: HP P2000 MSA -> HP C7000 Chassis -> HP Flex-10 -> Cisco Gigabit switch -> Cisco ASA -> WAN

wide-area-network bandwidth tcp latency

3 Answers

  1. IPERF is a very useful tool for testing throughput in situations like this.

    If different applications are getting different throughputs, it could be an issue with the application/server used, or that someone has implemented QoS (Quality of Service) on the link, so that the network limits traffic for some applications.

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  2. The upstream throughput on one of the sides may be getting throttled or there is some intermediate equipment/network throttling down the connection between the two points. One possible way to verify and maybe identify the situation is by utilizing a 3rd reference. In this case some of the speed test sites may be worth trying.

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  3. Comparing site to site data transfers against a Windows Update download from one site isn't exactly comparing apples to apples if you ask me.

    nicelink and nms-dpnss are hosts at each site, correct? cspuni is a host at one site connecting to the Windows Update web site, right? How are those two comparisons related? How is comparing a download between one host and an external web site against a file transfer between two hosts at each site helping you analyze the problem?

    My suggestion would be to test data transfers between multiple sets of hosts at each site and compare the results. Example:

    A<->B; C<->D; A<->D; B<->C

    Where A and C are at one site and B and D are at the other site.

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