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Enabling High Performance Data Transfers on Hosts:(Notes for Users and System Administrators)
Note: This original copy of this page is maintained at the Pittsburgh Supercomputing Center, at http://www.psc.edu/networking/perf_tune.html. Because the information in this page is updated frequently, we strongly recommend checking this URL to get the most up-to-date information on performance tuning for high speed networks.
Another Note: Many, many people have helped me to compile the information on this website. I want to thank all of them for their help in sending me updates, and encourage people to continue to report any errors or additions to me (email@example.com) so that the information herein will be as up-to-date as possible.
Alternatively, the system-wide default socket buffer size can be
raised, causing all applications to utilize large socket buffers.
This is not generally recommended, as many network applications then
consume system memory which they do not require.
New: The best solution would be for the operating system to
automatically tune socket buffers to the appropriate size. Jeff Semke
at PSC has developed an experimental Autotuning
Implementation for NetBSD which does exactly this. In the future,
we hope to see such automatic tuning as a part of all TCP
implementations, making this entire website obsolete.
For socket applications, the programmer can choose the socket buffer
sizes using a setsockopt() system call. A
Detailed Users Guide describing how to set socket buffer sizes
within socket based applications has been put together by Von Welch at
In order to take advantage of today's high speed networks, hosts must
support and utilize extensions to basic TCP/IP. There are four main
steps required for both the data sender and data receiver:
Alternatively, the system-wide default socket buffer size can be raised, causing all applications to utilize large socket buffers. This is not generally recommended, as many network applications then consume system memory which they do not require.
New: The best solution would be for the operating system to automatically tune socket buffers to the appropriate size. Jeff Semke at PSC has developed an experimental Autotuning Implementation for NetBSD which does exactly this. In the future, we hope to see such automatic tuning as a part of all TCP implementations, making this entire website obsolete.
For socket applications, the programmer can choose the socket buffer sizes using a setsockopt() system call. A Detailed Users Guide describing how to set socket buffer sizes within socket based applications has been put together by Von Welch at NCSA.
|Operating System (Alphabetical) (Click for additional info)||RFC1191 Path MTU Discovery||RFC1323 Support||Default maximum socket buffer size||Default TCP socket buffer size||Default UDP socket buffer size||Applications (if any) which are user tunable||RFC2018 SACK Support
|BSD/OS 2.0||No||Yes||256kB||8kB||9216 snd 41600 rcv||None||Hari Balakrishnan's BSD/OS 2.1 implementation|
|BSD/OS 3.0||Yes||Yes||256kB||8kB||9216 snd 41600 rcv||None|
|CRI Unicos 8.0||Yes||Yes||FTP|
|(Compaq) Digital Unix 3.2||Yes Winscale, No Timestamps||128kB||32kB||None|
|(Compaq) Digital Unix 4.0||Yes||Yes Winscale, No Timestamps||128kB||32kB||9216 snd 41600 rcv||None||PSC Research version|
Luigi Rizzo's FreeBSD2.1R version|
Also Eliot Yan of UCLA has one
|FTP Software (NetManage) OnNet Kernel 4.0 for Win95/98||Yes||Yes||963.75 MB||8K [146K for Satellite tuning]||8K send 48K recv||FTP server||Yes|
|HPUX 9.X||No||9.05 and 9.07 provide patches for RFC1323||1 MB (?)||8kB||9216||FTP (with patches)|
|IBM AIX 3.2 & 4.1||No||Yes||64kB||16kB||41600 Bytes recieve/9216 Bytes send||None|
|IBM MVS TCP stack by Interlink, v2.0 or greater||No||Yes||1MB|
|Linux 2.0.x||Yes||No (under development for 2.1.x)||32kB||32kB||32kB||None||Available from Theodoros Assimakopoulos (firstname.lastname@example.org)|
|Linux 2.1.90 or later, including Linux 2.2.||Yes||Yes||64kB||32kB (see notes||32kB(?)||None||SACK (and FACK?) are now part of the 2.1 distribution|
|MacOS (Open Transport)||Yes||Yes||limited only by available system RAM||32kB||64kB (send and receive)||Fetch (ftp client)||Not in versions up to Open Transport 2.7.x; will be in OT 3.0|
|Microsoft Windows NT 3.5/4.0||Yes||No||64kB||max(~8kB, min(4*MSS, 64kB))||No|
|Microsoft Windows NT 5.0 Beta||Yes||Yes|
|Microsoft Win95||Patch is available with many improvements to networking support. I have not tried out this patch, but I imagine the tuning instructions for Win98 will be helpful if you use it.|
|Microsoft Win98||Yes||1GB(?!)||8kB||Yes (on by default)|
|NetBSD 1.1/1.2||No||Yes||256kB||16kB||None||PSC Research version|
|SGI IRIX 5.3||Yes||Yes||512kB||60kB||None|
|SGI IRIX 6.1||Yes||Yes||1MB||60kB||None|
|SGI IRIX 6.2||Yes||Yes||Unlimitted||60kB||None|
|SGI IRIX 6.5||Yes||Yes||Unlimitted||60kB||60kB||None||Yes, as of 6.5.7. It is on by default.|
|SunOS 4.1.4||No||No. However, can be purchased as a Sun Consulting Special.||52kB||4kB||9000 bytes Send, 18032 bytes Receive||None|
|Sun Solaris 2.5||Yes||No. However, can be purchased as a Sun Consulting Special, and will be in Solaris 2.6||256kB||8kB||8kB||None|
|Sun Solaris 2.6||Yes||Yes||1MB TCP, 256kB UDP||8kB||8kB||None||Yes, experimental patch from Sun|
|Sun Solaris 7||Yes||Yes||1MB TCP, 256kB UDP||8kB||8kB||None||Yes; default is "passive". (See below)|
|Operating System (Alphabetical) (Click for additional info)||Path MTU Discovery||RFC1323 Support||Default maximum socket buffer size||Default TCP socket buffer size||Default UDP socket buffer size||Applications (if any) which are user tunable||SACK Support|
sysctl" interface described for FreeBSD. See sysctl(1) and sysctl(3) for more information.
/etc/netvar". Running "
/etc/netvar" with no arguments shows all configurable variables:
% /etc/netvar Network configuration variables tcp send space is 32678 tcp recv space is 32678 tcp time to live is 60 tcp keepalive delay is 14400 udp send space is 65536 udp recv space is 68096 udp time to live is 60 ipforwarding is on ipsendredirects is on subnetsarelocal is on dynamic MTU discovery is on adminstrator mtu override is on maximum number of allocated sockets is 3750 maximum socket buffer space is 409600 operator message delay interval is 5 per-session sockbuf space limit is 0The following variables can be set:
/etc/netvar, they take effect immediately for new processes. Processes which are already running with open sockets are not modified.
# dbx -k /vmunix (dbx) assign sb_max = (u_long) 524288 (dbx) patch sb_max = (u_long) 524288
In this example, sb_max is increased to 512kB. The first command changes the variable for the running system, and the second command patches the kernel so it will continue to use the new value, even after rebooting the system. Note, however, that reinstalling (overwriting) the kernel will undo this change.
% /sbin/sysconfig -q inet inet: tcp_sendspace = 32768 tcp_recvspace = 32768 tcp_keepidle = 14400 tcp_keepintvl = 150 tcp_keepinit = 150 tcp_keepcnt = 8 tcp_ttl = 60 tcp_mssdflt = 536 tcp_rttdflt = 3 tcp_dont_winscale = 0 tcpnodelack = 0 tcptwreorder = 1 udp_sendspace = 9216 udp_recvspace = 41600 udpcksum = 1 udp_ttl = 30 pmtu_enabled = 1 pmtu_rt_check_intvl = 20 pmtu_decrease_intvl = 1200 pmtu_increase_intvl = 240 ... % /sbin/sysconfig -q socket socket: sominconn = 0 somaxconn = 1024 sb_max = 131072To make a change (for example):
# /sbin/sysconfig -r inet tcp_sendspace 65536 # /sbin/sysconfig -r inet tcp_recvspace 65536
This document contains information on other important parameters (not just the ones directly associated with the socket, IP, and TCP layers) and gives instructions on how to modify things. It also includes important patch information, and is updated every few months.
You can't modify the maximum socket buffer size in FreeBSD 2.1.0-RELEASE, but
in 2.2-CURRENT you can use
sysctl -w kern.maxsockbuf=524288to make it 512kB (for example). You can also set the TCP and UDP default buffer sizes using the variables
net.inet.tcp.sendspace net.inet.tcp.recvspace net.inet.udp.recvspace
Many default settings, all of the above and more, may be overriden with registry entries. We plan to make available tuning guidelines at "some future time". Also default TCP window may be set with Statistics app which is installed with OnNet Kernel.
The product "readme" discusses changing TCP window size and Initial slow start threshold with the Windows registry.
Statistics also has interesting graphs of TCP/UDP/IP/ICMP traffic. Also IPtrace app is shipped with OnNet Kernel to view unicast / multicast / broadcast traffic (no unicast traffic for other hosts - it does not run in promiscuous mode).
There are patches for 9.05 and 9.07 that provide 1323 support. To enable it, one must poke the kernel variables tcp_dont_tsecho and tcp_dont_winscale to 0 with adb (the patch includes a script, but I don't recall the patch number).
Without the 9.05/9.07 patch, the maximum socket buffer buffer size is somewhere around 58254 bytes. With the patch it is somewhere around 1MB (there is a small chance it is as much as 4MB).
The FTP provided with the up to date patches should offer an option to change the socket buffer size. The default socket buffer size for this could be 32KB or 56KB.
There is no support for SACK in 9.X.
Up through 10.20, RFC 1323 support is like the 9.05 patch, except the maximum socket buffer size is somewhere between 240 and 256KB. In other words, you need to do the same adb "pokes" as described above.
10.30 does not require adb "pokes" to enable RFC1323. 10.30 also replaces nettune with ndd. The 10.X default TCP socket buffer size is 32768, the default UDP remains unchanged from 9.X. Both can be tweaked with nettune.
FTP should be as it is in patched 9.X.
There is no support for SACK in 10.X up through 10.20.
HP-UX 11supports PMTU discovery and enables it by default. This is controlled through the ndd setting ip_pmtu_strategy.
Note: Addition (extensive) information is available at ftp://ftp.cup.hp.com/dist/networking/briefs/annotated_ndd.txt
RFC 1323 support is enabled automagically in HP-UX 11. If an application requests a window/socket buffer size greater than 64 KB, window scaling and timestamps will be used automatically.
The default TCP window size in HP-UX 11 remains 32768 bytes and can be altered though ndd and the settings:
tcp_recv_hiwater_def tcp_recv_hiwater_lfp tcp_recv_hiwater_lnp tcp_xmit_hiwater_def tcp_xmit_hiwater_lfp tcp_xmit_hiwater_lnp
FTP in HP-UX 11 uses the new sendfile() system call. This allows data to be sent directly from the filesystem buffer cache through the network without intervening data copies.
Support for SACK in HP-UX 11 is currently (2/26/99) under investigation.
Here is some ndd -h parm output for a few of the settings mentioned above. For those not mentioned, use ndd -h on an HP-UX 11 system, or consult the online manuals at http://docs.hp.com/
# ndd -h ip_pmtu_strategy ip_pmtu_strategy: Set the Path MTU Discovery strategy: 0 disables Path MTU Discovery; 1 enables Strategy 1; 2 enables Strategy 2. Because of problems encountered with some firewalls, hosts, and low-end routers, IP provides for selection of either of two discovery strategies, or for completely disabling the algorithm. The tunable parameter ip_pmtu_strategy controls the selection. Strategy 1: All outbound datagrams have the "Don't Fragment" bit set. This should result in notification from any intervening gateway that needs to forward a datagram down a path that would require additional fragmentation. When the ICMP "Fragmentation Needed" message is received, IP updates its MTU for the remote host. If the responding gateway implements the recommendations for gateways in RFCM- 1191, then the next hop MTU will be included in the "Fragmentation Needed" message, and IP will use it. If the gateway does not provide next hop information, then IP will reduce the MTU to the next lower value taken from a table of "popular" media MTUs. Strategy 2: When a new routing table entry is created for a destination on a locally connected subnet, the "Don't Fragment" bit is never turned on. When a new routing table entry for a non-local destination is created, the "Don't Fragment" bit is not immediately turned on. Instead, o An ICMP "Echo Request" of full MTU size is generated and sent out with the "Don't Fragment" bit on. o The datagram that initiated creation of the routing table entry is sent out immediately, without the "Don't Fragment" bit. Traffic is not held up waiting for a response to the "Echo Request". o If no response to the "Echo Request" is received, the "Don't Fragment" bit is never turned on for that route; IP won't time-out or retry the ping. If an ICMP "Fragmentation Needed" message is received in response to the "Echo Request", the Path MTU is reduced accordingly, and a new "Echo Request" is sent out using the updated Path MTU. This step repeats as needed. o If a response to the "Echo Request" is received, the "Don't Fragment" bit is turned on for all further packets for the destination, and Path MTU discovery proceeds as for Strategy 1. Assuming that all routers properly implement Path MTU Discovery, Strategy 1 is generally better - there is no extra overhead for the ICMP "Echo Request" and response. Strategy 2 is available only because some routers, or firewalls, or end hosts have been observed simply to drop packets that have the DF bit on without issuing the "Fragmentation Needed" message. Strategy 2 is more conservative in that IP will never fail to communicate when using it. [0,2] Default: Strategy 2 # ndd -h tcp_recv_hiwater_def | more tcp_recv_hiwater_def: The maximum size for the receive window. [4096,-] Default: 32768 bytes # ndd -h tcp_xmit_hiwater_def tcp_xmit_hiwater_def: The amount of unsent data that triggers write-side flow control. [4096,-] Default: 32768 bytesHP has detailed networking performance information online, including information about the "netperf" tool and a large database of system performance results obtained with netperf:
See the "no" man page for options; additional information is available in the IBM manual AIX Versions 3.2 and 4.1 Performance Tuning Guide, which is available on AIX machines through the InfoExplorer hypertext interface.
If SCALE is not zero, and the user bufferspace is > 65535, negotiating window scaling and timestamps will be attempted.
If SCALE is not zero, and the remote user negotiates window scaling or timestamps, we will accept those requests.
Note: Linux only allows you to use 15 bits of the TCP window field. The net effect of this is that you need to multiply everything by 2, or recompile the kernel without this limitation. See "Tuning at compile time" below.
There is no sysctl application for changing values, but you can change the values very easy with a editor like vi. Simply edit the files listed below, which magically change the values in the kernel.
Tuning the default and maximum window size:
/proc/sys/net/core/rmem_default - default receive window /proc/sys/net/core/rmem_max - maximum receive window /proc/sys/net/core/wmem_default - default send window /proc/sys/net/core/wmem_max - maximum send window
In /proc/sys/net/ipv4/ you will find some other possibilities to tune TCP:
tcp_timestamps tcp_windowscaling tcp_sack ...You will find a short description in
/LINUX-SOURCE-DIR/include/linux/skbuff.h /* These are just the default values. This is run time configurable. * FIXME: Probably the config option should go away. - erics */ #ifdef CONFIG_SKB_LARGE #define SK_WMEM_MAX 65535 #define SK_RMEM_MAX 65535 #else #define SK_WMEM_MAX 32767 #define SK_RMEM_MAX 32767 #endifAlso in the Linux kernel source directory:
/LINUX-SOURCE-DIR/include/net/tcp.hyou can change the MAX-WINDOW value
/* * Never offer a window over 32767 without using window scaling. Some * poor stacks do signed 16bit maths! */ #define MAX_WINDOW 32767 #define MIN_WINDOW 2048
This last item is what limits you to using only 15 bits of the window field in the TCP packet header. Suppose you wish to use a window of 40 kB. If you simply set the rmem_default to 40 kB, the stack will recognize that this is less than 64 kB and therefore will not negotiate a winshift. However, because of this second check, you will only get 32 kB. Therefore, you need to set the rmem_default to something larger than 64 kB in order to force a winshift=1, which then lets you express the desired 40 kB in only 15 bits (and in fact you'll probably then end up with 64 kB whether you want it or not).
I imagine that a better idea is to simply change this value for MAX_WINDOW to 65535 if you need windows larger than 32 kB. I haven't tested this out to see how well it works. Alas, this part of the code is somewhat hard to follow. I'd appreciate any comments on how well this works.
User testimonial: With the tuned TCP stacks it was possible to get a maximum throughput between 1.5 - 1.8 Mbit/s via a 2Mbit/s satellite link, measured with netperf.
I don't have detailed information, however, someone pointed me to a good website with useful information. The URL is http://www.sustworks.com/products/prod_ottuner.html. I don't endorse the product they are selling (since I've never tried it). However, it is available for a free trial, and they appear to do an excellent job of describing perf-tune issues for Macs.
New: Some folks at NLANR/MOAT in SDSC have written a tool to do guide you through some of this stuff. It can be found at http://moat.nlanr.net/Software/TCPtune/.
Even newer: I've updated some sending window information which was inaccurate. See below.
Several folks have recently helped me to figure out how to accomplish the necessary tuning under Windows98, and the features do appear to exist and work. Thanks to everyone for the assistance! The new description below should be useful to even the complete Windows novice (such as me :-).
Windows98 includes implementation of RFC1323 and RFC2018. Both are on by default. (However, with a default buffer size of only about 8kB, window scaling doesn't do much).
Windows stores the tuning parameters in the Windows Registry. In the registry are settings to toggle on/off Large Windows, Timestamps, and SACK. In addition, default socket buffer sizes can be specified in the registry.
In order to modify registry variables, do the following steps:
TCP/IP Stack Variables
Support for TCP Large Windows (TCPLW)
Win98 TCP/IP supports TCP large windows as documented in RFC 1323. TCP large windows can be used for networks that have large bandwidth delay products such as high-speed trans-continental connections or satellite links. Large windows support is controlled by a registry key value in:
The registry key Tcp1323Opts is a string value type. The values for Tcp1323Opt are
|0||No Windowscaling and Timestamp Options|
|1||Window scaling but no Timestamp options|
|3||Window scaling and Time stamp options|
The default value for Tcp1323Opts is 3: Window Scaling and Time stamp options. Large window support is enabled if an application requests a Winsock socket to use buffer sizes greater than 64K. The current default value for TCP receive window size in Memphis TCP is 8196 bytes. In previous implementations the TCP window size was limited to 64K, this limit is raised to 2**30 through the use of TCP large window support.
Support for Selective Acknowledgements (SACK)
Win98 TCP supports Selective Acknowledgements as documented in RFC 2018. Selective acknowledgements allow TCP to recover from IP packet loss without resending packets that were already received by the receiver. Selective Acknowledgements is most useful when employed with TCP large windows. SACK support is controlled by a registry key value in:
The registry key SackOpts is a string value type. The values for SackOpts are
|0||No Sack options|
|1||Sack Option enabled|
Support for Fast Retransmission and Fast Recovery
Win98 TCP/IP supports Fast Retransmission and Fast Recovery of TCP connections that are encountering IP packet loss in the network. These mechanisms allow a TCP sender to quickly infer a single packet loss by reception of duplicate acknowledgements for a previously sent and acknowledged TCP/IP packet. This mechanism is useful when the network is intermittently congested. The reception of 3 (default value) successive duplicate acknowledgements indicates to the TCP sender that it can resend the last unacknowledged TCP/IP packet (fast retransmit) and not go into TCP slow start due to a single packet loss (fast recovery). Fast Retransmission and Recovery support is controlled by a registry key value in:
The registry key MaxDupAcks is DWORD taking integer values from 2 to N. If MaxDupAcks is not defined, the default value is 3.
Update: If you wish to set the default receiver window for applications, you should set the following key:
DefaultRcvWindow is a string type and the value describes the default receive windowsize for the TCP stack. Otherwise the windowsize has to be programmed in apps with setsockopt.
For a long time, I had the following sentence on this page:
If anyone has any further information on these specific applications under Windows, I would be happy to include it here.
Editor's note: See Windows 98 above for a detailed description of how this all works. In NT land, the Registry Editor is called regedt32.
Any Registry Values listed appear in: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters Receive Window maximum value = 64kB, since window scaling is not supported default value = min( max( 4 x MSS, 8kB rounded up to nearest multiple of MSS), 64kB) Registry Value: TcpWindowSize Path MTU Discovery Variables: EnablePMTUDiscovery (default = enabled) turn on/off path MTU discovery EnablePMTUBHDetect (default = disabled) turn on/off Black Hole detection Using Path MTU Discovery: EnablePMTUDiscovery REG_DWORD Range: 0 (false) or 1 (true) Default: 1 Determines whether TCP uses a fixed, default maximum transmission unit (MTU) or attempts to find the actual MTU. If the value of this entry is 0, TCP uses an MTU of 576 bytes for all connections to computers outside of the local subnet. If the value of this entry is 1, TCP attempts to discover the MTU (largest packet size) over the path to a remote host. Using Path MTU Discovery's "Blackhole Detection" algorithm: EnablePMTUBHDetect REG_DWORD Range: 0 (false) or 1 (true) Default: 0 If the value of this entry is 1, TCP tries to detect black hole routers while doing Path MTU Discovery. TCP will try to send segments without the Don't Fragment bit set if several retransmissions of a segment go unacknowledged. If the segment is acknowledged as a result, the MSS will be decreased and the Don't Fragment bit will be set in future packets on the connection.I received the following additional notes about the Windows TCP implementation.
PMTU Discovery. If PMTU is turned on, NT 3.1 cannot cope with routers that have the BSD 4.2 bug (see RFC 1191, section 5). It loops resending the same packet. Only confirmed on NT 3.1.
Editor's note: See Windows 98 above for more detailed descriptions of how this all works. I haven't personally tested the Win95 info below.
New: A Patch is available for Win95 at the following URL: http://support.microsoft.com/support/kb/articles/q182/1/08.asp. This patch includes support for TCPLW and SACK. I haven't tried it out, but I assume that the info above on tuning Win98 will be useful.
Any Registry Values listed appear in: HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\VxD\MSTCP Receive Window maximum value = 64kB, since window scaling is not supported default value = min( max( 4 x MSS, 8kB rounded up to nearest multiple of MSS), 64kB) Registry Value: DefaultRcvWindow Path MTU Discovery Variables: present Registry Values: PMTUDiscovery (default = 1 (enabled)) turn on/off path MTU discovery PMTUBlackHoleDetect (default = 0 (disabled)) turn on/off Black Hole detection (See NT for more info on using PMTU discovery and black hole detection).I received the following additional notes about the Windows TCP implementation.
TCP retries. Not strictly performance related but a common cause of TN3270 emulators dropping their sessions if the mainframe is busy for a second or two. Instead of retrying up to 240 seconds (RFC 1122, section 18.104.22.168), Windows 3.11 and 95 default to 5 retries without a time limit. Even with RTO doubling, on a fast link 5 retries gives up after less than a second of no response. Hkey_Local_Machine\System\CurrentControlSet\Services\VxD\MSTCP, add variable MaxDataRetries. I normally set it to 64.
The maximum socket buffer size can be modified by changing SB_MAX in /usr/src/sys/sys/socketvar.h.
The default socket buffer sizes can be modified by changing TCP_SENDSPACE and TCP_RECVSPACE in /usr/src/sys/netinet/tcp_usrreq.c.
It may also be necessary to increase the number of mbufs, NMBCLUSTERS in /usr/src/sys/arch/*/include/param.h.
Update: It is also possible to set these parameters in the kernel configuration file.
options SB_MAX=1048576 # maximum socket buffer size options TCP_SENDSPACE=65536 # default send socket buffer size options TCP_RECVSPACE=65536 # default recv socket buffer size options NMBCLUSTERS=1024 # maximum number of mbuf clusters
/var/sysgen/master.d/bsdThe following variables are available to enable control high speed transfers:
Only slightly related to this page, SGI Hippi performance info.
Under this version, there are two locations where configuration is done. Although I list the BSD information first, SGI recommends using systune which is described below.
The BSD values are now stored in /var/sysgen/mtune/bsd.
For instance from the file:
* name default minimum maximum * * TCP window sizes/socket space reservation; limited to 1Gbyte by RFC 1323 * tcp_sendspace 61440 2048 1073741824 tcp_recvspace 61440 2048 1073741824
These variables are used similarly to earlier IRIX 5 and 6 versions.
There is now a systune command. This command allows you to configure other networking variables. systune keeps strack of the chances you make in a file called stune so that you can see them all in one place. Also note that changes made using systune are permanent. Here is a sample of things which can be tuned using systune:
/usr/sbin/systune (which is like sysctl for BSD) is what you use for tuneable values. group: net_stp (statically changeable) stp_ttl = 60 (0x3c) stp_ipsupport = 0 (0x0) stp_oldapi = 0 (0x0) group: net_udp (dynamically changeable) soreceive_alt = 1 (0x1) arpreq_alias = 0 (0x0) udp_recvgrams = 2 (0x2) udp_sendspace = 61440 (0xf000) udp_ttl = 60 (0x3c) group: net_tcp (dynamically changeable) tcp_gofast = 0 (0x0) tcp_recvspace = 61440 (0xf000) tcp_sendspace = 61440 (0xf000) tcprexmtthresh = 3 (0x3) tcp_2msl = 60 (0x3c) tcp_mtudisc = 1 (0x1) tcp_maxpersistidle = 7200 (0x1c20) tcp_keepintvl = 75 (0x4b) tcp_keepidle = 7200 (0x1c20) tcp_ttl = 60 (0x3c) group: net_rsvp (statically changeable) ps_num_batch_pkts = 0 (0x0) ps_rsvp_bandwidth = 50 (0x32) ps_enabled = 1 (0x1) group: net_mbuf (statically changeable) mbretain = 20 (0x14) mbmaxpages = 16383 (0x3fff) group: net_ip (dynamically changeable) tcpiss_md5 = 0 (0x0) subnetsarelocal = 1 (0x1) allow_brdaddr_srcaddr = 0 (0x0) ipdirected_broadcast = 0 (0x0) ipsendredirects = 1 (0x1) ipforwarding = 1 (0x1) ipfilterd_inactive_behavior = 1 (0x1) icmp_dropredirects = 0 (0x0) group: network (statically changeable) netthread_float = 0 (0x0) group: inpcb (statically changeable) udp_hashtablesz = 2048 (0x800) tcp_hashtablesz = 8184 (0x1ff8)
Changes made using systune may or may not require a reboot. This can be easily determined by looking at the 'group' heading for each section of tunables. If the group heading says dynamic, changes can be made on the fly. Group headings labelled static require a reboot.
Finally, the tcp_sendspace and tcp_recvspace can be tuned on a per-interface basis using the rspace and sspace options to ifconfig.
SACK: As of 6.5.7, SACK is included in the IRIX operating system and is on by default.
The ndd variable tcp_max_buf specifies the maximum socket buffer size.
To change them, use:
ndd -set /dev/tcp tcp_max_buf xxx ndd -set /dev/tcp tcp_xmit_hiwat xxx ndd -set /dev/tcp tcp_recv_hiwat xxx
(Note: I believe xxx should be specified in bytes)
The ndd variable ip_path_mtu_discovery controls the use of path MTU discovery. The default value is 1, which means on.
Note that ndd can also be used to increase the volume of TCP connections available to a machine.
ndd -set /dev/tcp tcp_conn_req_max(where
In Solaris 2.6; and also 2.5 and 2.5.1 with newer tcp patches, the tcp_conn_req_max ndd setting has been removed, and split into two new settings:
tcp_conn_req_max_q default value = 128 number of connections in ESTABLISHED state (3-way handshake completed; not yet accepted) tcp_conn_req_max_q0 default value = 1024 number of connections in SYN_RCVD stateSACK is now available in an experimental release for Solaris 2.6. To obtain it, see ftp://playground.sun.com/pub/sack/tcp.sack.tar.Z
Additional Info about recent versions of solaris can be found at http://www.rvs.uni-hannover.de/people/voeckler/tune/EN/tune.html#thp
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This material is based in whole or in part on work supported by the National Science Foundation under Grant Nos. 9415552, 9870758, 9720674, or 9711091. Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation (NSF).
© Pittsburgh Supercomputing Center (PSC), Carnegie Mellon University
Revised: Tuesday, 09-Nov-1999 15:29:25 EST