Difference between tcp recv buffer and tcp receive window size?

Posted by pradeepchhetri on Server Fault See other posts from Server Fault or by pradeepchhetri
Published on 2012-11-05T10:48:39Z Indexed on 2012/11/05 11:05 UTC
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linux

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tcp

The command shows the tcp receive buffer size in bytes.

$ cat /proc/sys/net/ipv4/tcp_rmem 
4096    87380   4001344

where the three values signifies the min, default and max values respectively.

Then I tried to find the tcp window size using tcpdump command.

 $ sudo tcpdump -n -i eth0 'tcp[tcpflags] & (tcp-syn|tcp-ack) == tcp-syn and port 80 and host google.com' 
 tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
 listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes
 16:15:41.465037 IP 172.16.31.141.51614 > 74.125.236.73.80: Flags [S], seq 3661804272,  win  14600, options [mss 1460,sackOK,TS val 4452053 ecr 0,nop,wscale 6], length 0

I got the window size to be 14600 which is 10 times the size of MSS.

Can anyone please tell me the relationship between the two.

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