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Can anyone help me to find the max congestion window value for TCP in ubuntu? I only find the init window size; I can’t find the max. I only can find the init window size . i need the max , it is related to buffer size of tcp ?

tila tila
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2 Answers2

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Can anyone help me to find the max congestion window value for TCP in ubuntu?

Command 

sysctl net.ipv4.tcp_wmem

will output something like 

net.ipv4.tcp_wmem = 4096    16384   4194304

the last value (4194304) is the maximum congestion window.

user2768
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It depends on the send window. With window scale option, you can find the limits of send windows here: https://en.wikipedia.org/wiki/TCP_window_scale_option

You may want to take a look into the actual implementation and may find the following useful: 1. general tcp implementation: https://github.com/torvalds/linux/blob/6f0d349d922ba44e4348a17a78ea51b7135965b1/net/ipv4/tcp.c 2. TCP cubic variant: https://github.com/torvalds/linux/blob/6f0d349d922ba44e4348a17a78ea51b7135965b1/net/ipv4/tcp_cubic.c

The are various variants of TCP congestion control - you can find what flavour you are using based on: https://superuser.com/questions/992919/how-to-check-the-tcp-congestion-control-algorithm-flavour-in-ubuntu

Eran Rosenthal
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