kern/42547: cannot establish connections after setting net.inet.tcp.recvspace sysctl to 256K

[Constantine Aleksandrovich Murenin <C++%Cns.SU@localhost>]

>Number:         42547
>Category:       kern
>Synopsis:       cannot establish connections after setting 
>net.inet.tcp.recvspace sysctl to 256K
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Dec 31 03:25:00 +0000 2009
>Originator:     Constantine A. Murenin (cnst) 
><cnst+netbsd%bugmail.mojo.ru@localhost>
>Release:        NetBSD 5.0.1
>Organization:
        David R. Cheriton School of Computer Science,
        University of Waterloo
>Environment:

# sysctl net.inet.tcp.{recv,send}space kern.mbuf.nmbclusters
net.inet.tcp.recvspace = 229376
net.inet.tcp.sendspace = 49152
kern.mbuf.nmbclusters = 65536

Architecture: i386
Machine: i386

>Description:
        I'm on a university network and I want to achieve 100 Mbps download 
        speeds from NetBSD mirrors.

        Setting the net.inet.tcp.recvspace sysctl to 224K works, but 
        setting it higher, for example, to 256K, stops ftp(1) and 
        other programs from working.

>How-To-Repeat:

dale# cd /tmp
dale# ftp 
ftp://ftp2.us.NetBSD.org/pub/NetBSD/NetBSD-5.0.1/i386/installation/cdrom/boot.iso
Connected to netbsd.mirrors.tds.net.
220-
220-
220-Welcome to TDS Internet Services - mirror3.mirrors.tds.net FTP service.
220-
220 
331 Please specify the password.
230 Login successful.
Remote system type is UNIX.
Using binary mode to transfer files.
200 Switching to Binary mode.
250 Directory successfully changed.
250 Directory successfully changed.
250 Directory successfully changed.
250 Directory successfully changed.
250 Directory successfully changed.
250 Directory successfully changed.
local: boot.iso remote: boot.iso
229 Entering Extended Passive Mode (|||62604|)
150 Opening BINARY mode data connection for boot.iso (6518784 bytes).
100% 
|*******************************************************************************************************************|
  6366 KiB    6.26 MiB/s    00:00 ETA
226 File send OK.
6518784 bytes received in 00:01 (6.09 MiB/s)
221 Goodbye.
dale# sysctl -w net.inet.tcp.recvspace=262144
net.inet.tcp.recvspace: 229376 -> 262144
dale# ftp 
ftp://ftp2.us.NetBSD.org/pub/NetBSD/NetBSD-5.0.1/i386/installation/cdrom/boot.iso
ftp: Can't create socket to determine default socket sizes: No buffer space 
available
dale# traceroute ftp2.us.NetBSD.org
traceroute to netbsd.mirrors.tds.net (216.165.129.141), 64 hops max, 40 byte 
packets
 1  dccore-nsfw02-csresearch1net.uwaterloo.ca (129.97.7.1)  0.201 ms  0.157 ms  
0.144 ms
 2  172.19.5.1 (172.19.5.1)  2.151 ms  2.283 ms  1.865 ms
 3  172.19.1.18 (172.19.1.18)  2.327 ms  1.969 ms  1.859 ms
 4  v720-cn-rt-phy.uwaterloo.ca (129.97.1.77)  0.413 ms  0.355 ms  0.346 ms
 5  ext-rt-mc-cn-rt-phy.uwaterloo.ca (129.97.1.10)  0.363 ms  0.343 ms  0.340 ms
 6  te3-5.1220.mpd01.yyz02.atlas.cogentco.com (38.99.202.213)  6.788 ms  6.740 
ms  6.821 ms
 7  te8-7.mpd01.ord01.atlas.cogentco.com (154.54.27.249)  22.223 ms 
te2-2.mpd01.ord01.atlas.cogentco.com (154.54.6.18)  21.847 ms 
te7-8.mpd01.ord01.atlas.cogent
co.com (154.54.2.161)  21.914 ms
 8  te1-1.mpd01.ord03.atlas.cogentco.com (154.54.2.94)  21.928 ms  22.194 ms  
22.007 ms
 9  savvis.ord03.atlas.cogentco.com (154.54.10.246)  22.059 ms  22.039 ms 
ber1-ge-8-8.chicagoequinix.savvis.net (208.173.176.185)  22.158 ms
10  208.172.13.198 (208.172.13.198)  22.521 ms  22.016 ms  22.170 ms
11  chcgildtcor01-gi3-0-0.network.tds.net (64.50.224.214)  22.084 ms  21.993 ms 
 22.031 ms
12  mdsnwigjlcr52-gi5-1.network.tds.net (64.50.228.134)  27.899 ms  27.778 ms  
27.849 ms
13  mirror3-eth0.mirrors.tds.net (216.165.129.141)  26.820 ms  26.736 ms  
26.787 ms
dale# 


>Fix: