TCP connections slow to 1 packet, every 120 seconds

Have an unusual condition and trying to find a mechanism that would cause this.

Have a Internet location where download wilsl randomly slow until near complete stop. Not everyone, by a too high percentage. All major sites show issue... Microsoft, McAFee, CNet, Youtube, anything.

We've done Wireshark captures. There are no retransmissions, no corrupt packets, no loss. The delay between packets will logarithmically increase until it quickly reaches 120 seconds. From the client's perspective

Received packet from Microsoft. ACK sent immediately EXACTLY 120 seconds Received packet from Microsoft. ACK sent immediately EXACTLY 120 seconds Received packet from Microsoft. ACK sent immediately

The delay incremented in one test as so rapdi exchange of packet for the first two seconds, then @2.1 seconds @2.3 seconds @2.5 seconds @2.9 seconds @3.1 seconds @3.9 seconds @4.2 seconds @5.9 seconds @9.4 seconds @16.4 seconds @30.3 seconds @57.8 seconds @112.5 seconds @221.7 seconds @342.0 seconds @462.4 seconds @582.6 seconds ... every 120 seconds for next half hour--then capture closed

120 seconnds is clearly a timer of some sort, but I can't figure out what would cause a service to hold off sending the next packet for 120 seconds... Or what device would buffer such a thing for 120 secs.

Again, no re-transmissions. Each packet is a new packet, different. the transfer continues at a rate of one 1,514 byte packet every 120 seconds. This is happening to servers, desktops & laptops across a site.

It only occurs with TCP transfers. We have UDP connections between the sites that are unaffected. Not affecting local LAN-to-LAN. SO the problem is either on our Cisco 2821 (WAN/Internet router) or within our ISP. ISP has been doing good faith tests and investigation without results.

Just fishing for ideas of what would hold back the next packet for 120 seconds, yet not be re-transmissions, corrupt packets, or loss of packets.

Reply to
Royal Frazier
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Reply to
D. Stussy

Firstly are the sequence numbers incrementing with each new received packet? If not then it is simply that your acks are not getting through.

This seems by far the most likely.

Below is some other stuff I had already written which may be worth a look if the above does not explain the behaviour.

What TCP options are being used? Look in the SYN packets in wireshark and post options from both sides here. What are *your* receive windows? i.e. what receive windows are being offered by you in acks to the far hosts?

The sending TCP should do something like send one packet extra for every ack received. For some reason this is not happening.

Also set up a couple of instances of say pingplotter (30 day free trial) and ping a couple or three big fancy popular web sites with full size packets every second for ever. Look for anomalies. May as well do small packets too.

Could ALSO consider TCP with pingplotter too. It does close the session properly so will not leave

1,000's of dangling connections sucking the life out of your target.

My first idea is that your ISP or your firewall is likely doing something that is affecting the service and this is driving the far end TCPs into a state from which it is difficult or impossible for them to recover.

You have rebooted your firewall? Recent firwall software upgrades/config changes.

I forget the definition now but I will look it up, Slow Start is a TCP state:) This of course won't help you since it is whatever is getting them into this behaviour that is the real problem.

It could of course be a problem on your site too.

Let's have some more details of your site and internet connection. Whatever you think might be relevant. Also - do you do any QoS, rate limiting, traffic shaping or anything like that?

The email in the header works, I don't normally use it but if you like send a wireshark file and I can have a look to see if I can spot it in all the spam:)

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