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inteq
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Location: Romania

Detect ISP limiting packets/second

Wed Nov 23, 2022 6:44 am

Hello,

Can one detect if the ISP is limiting pps between two locations?
Might be totally wrong, but in Winbox, under IP/Firewall/Connections, if selecting Orig./Repl. Packets and filtering the connection in question, the amout of orig. packets should match the reply packets closely, correct? (might be totally wrong here)
If reply packets value fails to keep up with orig. packets, does that mean the ISP is somehow limiting the packets/second?

The application I am using is sending/receiving a lot of packets.
The location in question has just been installed yesterday.
For example, in 80 seconds 44K packets and ~20 MB of traffic (sql traffic)

Why do I think the ISP is somehow limiting pps: yesterday while testing, the application took 80 seconds to complete. Today, I think after the ISP finished setting up the new location's bandwidth limitation and other security settings, the same procedure in the aplication takes 145 seconds, almost double.
Bandwidth between locations (same provider) is 1 Gbps up/down with 150 Mbps minimum garanteed, so bandwidth should not be a problem for a mere 20 MB of traffic.

If I am totally wrong with my Orig./Repl. Packets idea, any other way to check?

Thank you.
 
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mkx
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Re: Detect ISP limiting packets/second

Wed Nov 23, 2022 9:24 am

TCP supports a feature sometimes referred to as "aggregate ACK" ... which means that receiver doesn't ACK every TCP packet received, it can ACK multiple packets in a single ACK packet. What I observed is that many TCP stacks ACK two received packets at the time if ingress TCP packet flow is more or less constant. Individual TCP packets will be ACKed if packets arrive in longer interfvals, but in this case ACK can be delayed. But everything really depend on particular TCP stack implementation (on both ends of TCP connection), so it's not exactly trivial to debug such things.

It is fairly simple to check if ISP is throttling according to PPS if you run iperf3 test and change MSS (-M, --set-mss n) to small numbers, default is to use largest possible size, which is MTU-40 bytes (40 bytes being IP/TCP header size). If by changing packet sizes you always reach similar packet rate, then ISP is limiting PPS. If it varies a lot, then the problem can be something different.
 
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inteq
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Posts: 402
Joined: Wed Feb 25, 2015 8:15 pm
Location: Romania

Re: Detect ISP limiting packets/second

Wed Nov 23, 2022 4:42 pm

Thank you mkx. Will try iperf3.

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