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Commands Reference, Volume 4

no Command

Purpose

Manages network tuning parameters.

Syntax

no [ -p | -r ] { -o Tunable[=NewValue] }

no [ -p | -r ] {-d Tunable }

no [ -p | -r ] { -D }

no -a

no -?

no -h Tunable

no -L Tunable

Note
Multiple flags -o, -d, and -L are allowed.

Description

Use the no command to configure network tuning parameters. The no command sets or displays current or next boot values for network tuning parameters. This command can also make permanent changes or defer changes until the next reboot. Whether the command sets or displays a parameter is determined by the accompanying flag. The -o flag performs both actions. It can either display the value of a parameter or set a new value for a parameter. When the no command is used to modify a network option it logs a message to the syslog using the LOG_KERN facility. For a more information on how the network parameters interact with each other, refer to the AIX 5L Version 5.2 System Management Guide: Communications and Networks.

Attention: Be careful when you use this command. If used incorrectly, the no command can cause your system to become inoperable.

Flags

-a Displays current, reboot (when used in conjunction with -r) or permanent (when used in conjunction with -p) value for all tunable parameters, one per line in pairs Tunable = Value. For the permanent options, a value only displays for a parameter if its reboot and current values are equal. Otherwise NONE displays as the value.
-d Tunable Resets Tunable its to default value. If Tunable needs to be changed (that is it is currently not set to its default value) and it is of type Bosboot or Reboot, or if it is of type Incremental and has been changed from its default value, and -r is not used in combination, it is not changed but a warning displays instead.
-D Resets all tunables to their default value. If a tunable needing to be changed are of type Bosboot or Reboot, or if they are of type Incremental and have been changed from their default value, and neither -p nor -r are used in combination, they will not be changed but a warning displayd instead.
-h Tunable Displays help about Tunable parameters.
-o Tunable [=NewValue ] Displays the value or sets the Tunable to NewValue. If a tunable needs to be changed (the specified value is different than current value), and is of type Bosboot or Reboot, or if it is of type Incremental and its current value is bigger than the specified value, and -r is not used in combination, it will not be changed but a warning displays instead.

When -r is used in combination without a new value, the nextboot value for Tunable is displayed. When -p is used in combination without a new value, a value displays only if the current and next boot values for tunable are the same Otherwise NONE displays as the value.

-p Makes changes apply to both current and reboot values when used in combination with -o, -d or -D, that is turns on updating of the /etc/tunables/nextboot file in addition to the updating of the current value. These combinations cannot be used on Reboot and Bosboot type parameters because their current value can't be changed.

When used with -a or -o without specifying a new value, values displays only if the current and next boot values for a parameter are the same. Otherwise NONE displays as the value.

-r Makes changes apply to reboot values when used in combination with -o, -d or -D , that is is turns on the updating of the /etc/tunables/nextboot file. If any parameter of type Bosboot is changed, the user is prompted to run bosboot. When used with -a or -o without specifying a new value, next boot values for tunables display instead of the current values.
-L Tunable Lsts the characteristics of one or all Tunables, one per line, using the following format:
Name   Current  Default  Reboot   Minimum  Maximum  Unit  Type Dependencies
       value    value    value    value    value
----------------------------------------------------------------------------
param1 5        2        4        1        10       MB/s     I  param2 
                                                                param3
Parameters can be of the following types:
  • D for Dynamic if tunable can be changed at any time
  • S for Static if tunable can never be changed
  • R for Reboot if tunable can only be changed during reboot sequence.
  • B for Bosboot if tunable can only be changed by running bosboot and rebooting machine
  • M for Mount if tunable is only effective for future filesystems or directory mountings
  • I for Incremental if tunable can only be incremented, except at boot time
-? Displays the usage of the no command.

Any change (with -o, -d, or -D) to a parameter of type Mount results in a message sdisplaying to warn the user that the change is only effective for future mountings.

Any attempt to change (with -o, -d, or -D) a parameter of type Bosboot or Reboot without -r, results in an error message.

Any attempt to change (with -o, -d, or -D but without -r) the current value of a parameter of type Incremental with a new value smaller than the current value, results in an error message.

Note
The current set of parameters managed by the no command only includes Reboot, Static and Dynamic types.

Compatibility Mode

When running in pre 5.2 compatibility mode (controlled by the pre520tune attribute of sys0, see Introduction to AIX 5L Version 5.2 tunable parameter setting in the Performance Management Guide), reboot values for parameters, except those of type Bosboot, are not really meaningful because in this mode they are not applied at boot time.

In pre 5.2 compatibility mode, setting reboot values to tuning parameters continues to be achieved by imbedding calls to tuning commands in scripts called during the boot sequence. Parameters of type Reboot can therefore be set without the -r flag, so that existing scripts continue to work.

This mode is automatically turned ON when a machine is MIGRATED to AIX 5L Version 5.2. For complete installations, it is turned OFF and the reboot values for parameters are set by applying the content of the /etc/tunables/nextboot file during the reboot sequence. Only in that mode are the -r and -p flags fully functional. See AIX 5L Version 5.2 kernel tuning in the Performance Tools Guide and Reference for details about the new 5.2 mode.

Network Tunable Parameters

arpqsize
Purpose:
Specifies the maximum number of packets to queue while waiting for ARP responses.
Value:
  • Default: 1
  • Range: 1 to MAXSHORT
  • Type: Dynamic
Diagnosis:
N/A
Tuning
This parameter is supported by Ethernet, 802.3, Token-Ring and FDDI interfaces. The arpqsize value is increased to a minimum value of 5 when path MTU discovery is enabled. The value will not automatically decrease if path MTU discovery is subsequently disabled. This parameter applies to AIX 4.1.5, AIX 4.2.1 and later
Refer To:
Managing Tunable SP Parameters
arpt_killc
Purpose:
Specifies the time in minutes before a complete ARP entry will be deleted.
Value:
  • Default: 20
  • Range: 0 to MAXSHORT
  • Type: Dynamic
Diagnosis:
N/A
Tuning
To reduce ARP activity in a stable network, you can increase arpt_killc.
Refer To:
SP System-Specific Tuning Recommendations
arptab_bsiz
Purpose:
Specifies Address Resolution Protocol (ARP) table bucket size.
Value:
  • Default: 7
  • Range: 1 to MAXSHORT
  • Type: Reboot


Diagnosis:
N/A
Tuning
N/A
Refer To:
SP System-Specific Tuning Recommendations
arptab_nb
Purpose:
Specifies the number of ARP table buckets.
Value:
  • Default: 25
  • Range: 1 to MAXSHORT
  • Type: Reboot
Diagnosis:
N/A
Tuning
Increase this value for systems that have a large number of clients or servers. The default provides for 25 x 7 = 175 ARP entries, but assumes an even task distribution.
Refer To:
SP System-Specific Tuning Recommendations
bcastping
Purpose:
Allows response to ICMP echo packets to the broadcast address.
Value:
  • Default: 0 (off)
  • Range: 0 or 1
  • Type: Dynamic
Diagnosis:
N/A
Tuning
N/A
clean_partial_conns
Purpose:
Specifies whether or not SYN (synchronizes the sequence number) attacks are being avoided.
Value:
  • Default: 0 (off)
  • Range: 0 or 1
  • Type: Dynamic
Diagnosis:
N/A
Tuning
This option should be turned on for servers that need to protect against network attacks. If on, randomly removes partial connections to make room for new non-attack connections.
delayack
Purpose:
Delays acknowlegements (ACK) for certain TCP packets and attempts to piggyback them with the next packet sent instead.
Value:
  • Default: 0
  • Range: 0 to 3
  • Type: Dynamic
Diagnosis:
N/A
Tuning
This action will only be performed for connections whose destination port is specified in the list of the delayackports parameter. This can be used to increase performance when communicating with an HTTP server by reducing the total number of packets sent. The parameter can have one of four values:
  • 0 No delays; normal operation
  • 1 Delay the ACK for the server's SYN (Synchronizes the sequence numbers)
  • 2 Delay the ACK for the server's FIN (Sender has reached the end of its byte stream)
  • 3 Delay both the ACKs for the SYN and FIN.
delayackports
Purpose:
Specifies the list of destination ports for which the operation defined by the delayack port option will be performed.
Value:
  • Default: {}
  • Range: List of port numbers
  • Type: Dynamic
Diagnosis:
N/A
Tuning
The parameter takes a list of up to ten ports, separated by commas and enclosed in curly braces. For example:
no -o delayackports={80,30080}
To clear the list, set the option to {}.
dgd_packets_lost
Purpose:
Specifies how many consecutive packets must be lost before Dead Gateway Detection decides that a gateway is down.
Value:
  • Default: 3
  • Range: 1 to MAXSHORT
  • Type: Dynamic
Diagnosis:
N/A
Tuning
N/A
dgd_ping_time
Purpose:
Specifies how many seconds should pass between pings of a gateway by Active Dead Gateway Detection.
Value:
  • Default: 5
  • Range: 1 to MAXINT
  • Type: Dynamic
Diagnosis:
N/A
Tuning
dgd_retry_time
Purpose:
Specifies how many minutes a route's cost should remain raised when it has been raised by Passive Dead Gateway Detection. After this many minutes pass, the route's cost is restored to its user-configured value.
Value:
  • Default: 5
  • Range: 1 to MAXSHORT
  • Type: Dynamic
Diagnosis:
N/A
Tuning
N/A
directed_broadcast
Purpose:
Specifies whether to allow a directed broadcast to a gateway.
Value:
  • Default: 1(on)
  • Range: 0 or 1
  • Type: Dynamic
Diagnosis:
N/A
Tuning
The value of 1 allows packets to be directed to a gateway to be broadcast on a network on the other side of the gateway.
extendednetstats
Purpose:
Enables more extensive statistics for network memory services.
Value:
  • Default: 0(off)
  • Range: 0 or 1
  • Type: Reboot
Diagnosis:
N/A
Tuning
The default for this parameter is 0, for off, because these extra statistics cause a reduction in system performance.
fasttimo
Purpose:
Allows you to set the millisecond delay for the TCP fast timeout timer. This timeout controls how often the system scans the TCP control blocks to send delayed acknowledgments.
Value:
  • Default: 200
  • Range: 50 to 200 milliseconds
  • Type: Dynamic
Diagnosis:
N/A
Tuning
Reducing this timer value may improve performance with some non-IBM systems. However, this may also result in slightly increased system utilization.
icmp6_errmsg_rate
Purpose:
Specifies the upper limit for the number of ICMP v6 error messages that can be sent per second. This prevents excessive bandwidth being used by ICMP v6 error messages.
Value:
  • Default: 10 msg/sec
  • Range: 1 to 255
  • Type: Dynamic


Diagnosis:
N/A
Tuning
N/A
icmpaddressmask
Purpose:
Specifies whether the system responds to an ICMP address mask request.
Value:
  • Default: 0(off)
  • Range: 0 or 1
  • Type: Dynamic
Diagnosis:
N/A
Tuning
If the default value 0 is set, the network silently ignores any ICMP address mask request that it receives.
ie5_old_multicast_mapping
Purpose:
Specifies IP multicasts on Token-Ring should be mapped to the broadcast address rather than a functional address when value 1 is used.
Value:
  • Default: 0(off)
  • Range: 0 or 1
  • Type: Dynamic
Diagnosis:
N/A
Tuning
N/A
ifsize
Purpose:
Specifies the maximum number of network interface structures per interface.
Value:
  • Default: Number of interfaces in the system
  • Range:
  • Type: Reboot
Diagnosis:
N/A
Tuning
In AIX 4.3, the /etc/rc.net script automatically determines the number of interfaces on the system and sets ifsize to that value. Therefore, there is no reason to alter this parameter.
Refer To:
Managing Tunable SP Parameters
inet_stack_size
Purpose:
Specifies size of inet interrupt stack table in kilobytes.
Value:
  • Default: 16
  • Range: 1 to MAXSHORT
  • Type: Reboot
Diagnosis:
N/A
Tuning
This is needed if you were running with unoptimized debug kernel or the netinet kernel extension. This is different from the pin more stack code (which is not configurable) because this is on interrupt. This parameter only needs to be changed if there is a system panic due to interrupt stack overflow.
ipforwarding
Purpose:
Specifies whether the kernel should forward packets.
Value:
  • Default: 0(off)
  • Range: 0 or 1
  • Type: Dynamic
Diagnosis:
N/A
Tuning
Set this parameter to 1, if the system is acting as an IP router.
Refer To:
traceroute command
ipfragttl
Purpose:
Specifies the time to live for IP fragments in half-seconds.
Value:
  • Default: 60
  • Range: 60 to 255
  • Type: Dynamic
Diagnosis:
Fragments dropped after timeout (netstat -p ip).
Tuning
If value of IP: fragments dropped after timeout is nonzero, increasing ipfragttl may reduce retransmissions.
Refer To:
IP Layer
ipignoreredirects
Purpose:
Specifies whether to process redirects that are received.
Value:
  • Default: 0(does redirects)
  • Range: 0 or 1(1 ignores redirects)
  • Type: Dynamic
Diagnosis:
N/A
Tuning
This option only applies to AIX 4.2.1 or later.
ipqmaxlen
Purpose:
Specifies the number of received packets that can be queued on the IP protocol input queue.
Value:
  • Default: 100
  • Range: 100 to MAXINT
  • Type: Dynamic
Diagnosis:
Examine ipintrq overflows (netstat -s) or use crash to access IP input queue overflow counter.
Tuning
Increase size if system is using a lot of loopback sessions. Most operating system network drives call IP directly and do not use the IP queue. On these devices increasing ipqmaxlen has no effect.
Refer To:
IP Layer and IP Protocol Performance Tuning Recommendations
ipsendredirects
Purpose:
Specifies whether the kernel should send redirect signals.
Value:
  • Default: 1(send redirects)
  • Range: 0(do not send redirects) or 1
  • Type: Dynamic
Diagnosis:
N/A
Tuning
This is a configuration decision with performance consequences.
ipsrcrouteforward
Purpose:
Specifies whether the system forwards source-routed packets.
Value:
  • Default: 1(on)
  • Range: 0 or 1
  • Type: Dynamic
Diagnosis:
N/A
Tuning
The default value of 1 allows the forwarding of source-routed packets. A value of 0 causes all source-routed packets that are not at their destinations to be discarded. This parameter only applies to AIX 4.2.1 or later.
ipsrcrouterecv
Purpose:
Specifies whether the system accepts source-routed packets.
Value:
  • Default: 0(off)
  • Range: 0 or 1
  • Type: Dynamic
Diagnosis:
N/A
Tuning
The default value of 0 causes all source-routed packets destined for this system to be discarded. A value of 1 allows source-routed packets to be received. This parameter only applies to AIX 4.2.1 or later.
ipsrcroutesend
Purpose:
Specifies whether applications can send source-routed packets.
Value:
  • Default: 1(on)
  • Range: 0 or 1
  • Type: Dynamic
Diagnosis:
N/A
Tuning
The default value of 1 allows source-routed packets to be sent. A value of 0 causes setsockopt() to return an error if an application attempts to set the source routing option, and removes any source routing options from outgoing packets. This parameter only applies to AIX 4.2.1 or later.
ip6_defttl
Purpose:
Specifies the default hop count that is used for Internet Protocol Version 6 (IPv6) packets if no other hop count is specified.
Value:
  • Default: 64
  • Range: 1 to 255
  • Type: Dynamic
Diagnosis:
N/A
Tuning
N/A
ip6_prune
Purpose:
Specifies how often to check the IPv6 routing table for expired routes in seconds.
Value:
  • Default: 2
  • Range: 1 to MAXINT
  • Type: Dynamic
Diagnosis:
N/A
Tuning
N/A
ip6forwarding
Purpose:
Specifies whether the kernel should forward IPv6 packets.
Value:
  • Default: 0(off)
  • Range: 0 or 1
  • Type: Dynamic
Diagnosis:
N/A
Tuning
The default value of 0 prevents forwarding of IPv6 packets when they are not for the local systems. A value of 1 enables forwarding.
ip6srcrouteforward
Purpose:
Specifies whether the system forwards source-routed IPv6 packets.
Value:
  • Default: 1(on)
  • Range: 0 or 1
  • Type: Dynamic
Diagnosis:
N/A
Tuning
The default value of 1 allows the forwarding of source-routed packets. A value of 0 causes all source-routed packets that are not at their destinations to be discarded.
llsleep_timeout
Purpose:
Specifies timeout value in seconds for link local timeouts (used when multi_homed=1)
Value:
  • Default: 3
  • Range: 1 to MAXINT
  • Type: Dynamic
Diagnosis:
N/A
Tuning
N/A
main_if6
Purpose:
Specifies the interface to use for link local addresses. This is only used by autoconf6 to set up initial routes.
Value:
  • Default: 0
  • Range: 0 or 1
  • Type: Dynamic
Diagnosis:
N/A
Tuning
N/A
main_site6
Purpose:
Specifies the interface to use for site local address routing. This is only used if multi_homed is set to 3
Value:
  • Default: 0
  • Range: 0 or 1
  • Type: Dynamic
Diagnosis:
N/A
Tuning
N/A
maxnip6q
Purpose:
Specifies the maximum number of IPv6 packet-reassembly queues.
Value:
  • Range: 1 to MAXSHORT
  • Type: Dynamic
Diagnosis:
N/A
Tuning
N/A
maxttl
Purpose:
Specifies the time to live for Routing Information Protocol (RIP) packets in seconds.
Value:
  • Default: 255
  • Range: 1 to 255
  • Type: Dynamic
Diagnosis:
N/A
Tuning
N/A
multi_homed
Purpose:
Specifies the level of multi-homed IPv6 host support.
Value:
  • Default: 1
  • Range: 0 to 3
  • Type: Dynamic
Diagnosis:
N/A
Tuning
This will only be performed for connections whose destination port is specified in the list of the delayackports parameter. This can be used to increase performance when communicating with an HTTP server. The parameter can have one of four values:
  • 0 - Indicates the original functionality in AIX 4.3.
  • 1 - Indicates that link local addresses will be resolved by querying each interface for the link local address.
  • 2 - Indicates that link local addresses will only be examined for the interface defined by main_if6.
  • 3 - Indicates that link local addresses will only be examined for the interface defined by main_if6, and site local addresses will only be routed for the main_site6 interface.
nbc_limit
Purpose:
Specifies the total maximum amount of memory that can be used for the Network Buffer Cache (NBC) in Kbytes.
Value:
  • Default: derived from thewall
  • Range: 0 to MAXINT
  • Type: Dynamic
Diagnosis:
N/A
Tuning
When the cache grows to this limit, the least-used caches are flushed out of cache to make room for the new ones. This parameter only applies to AIX 4.3.2 or later. NBC is only used by the send_file() API and some Web servers that use the get engine in the kernel.
nbc_max_cache
Purpose:
Specifies the maximum size of the cache object allowed in the Network Buffer Cache (NBC) in bytes.
Value:
  • Default: 131072(128K)
  • Range: 1 to MAXINT
  • Type: Dynamic
Diagnosis:
N/A
Tuning
Data object bigger than this size is not be put in the NBC. This parameter only applies to AIX 4.3.2 or later. NBC is only used by the send_file() API and some Web servers that use the get engine in the kernel.
nbc_min_cache
Purpose:
Specifies the minimum size of the cache object allowed in the Network Buffer Cache (NBC) in bytes.
Value:
  • Default: 1 byte
  • Range: 1 to 131072(128K)
  • Type: Dynamic
Diagnosis:
N/A
Tuning
Data object smaller than this size is not be put in the NBC. This parameter only applies to Version 4.3.2 or later. NBC is only used by the send_file() API and some Web servers that use the get engine in the kernel
nbc_pseg (AIX 4.3.3 and later)
Purpose:
Specifies the maximum number of private segments that can be created for the Network Buffer Cache (NBC).
Value:
  • Default: 0
  • Range: 0 to MAXSHORT
  • Type: Dynamic
Diagnosis:
N/A
Tuning
When this option is set to a nonzero value, data objects with size between the size specified in nbc_max_cache and the segment size (256 MB) will be cached in a private segment. Data objects bigger than the segment size will not be cached at all. When this many private segments exist in NBC, cache data in private segments may be flushed for new cache data so the number of private segments will not exceed the limit. When this option is set to 0, all cache in private segments will be flushed.
nbc_pseg_limit (AIX 4.3.3 and later)
Purpose:
Specifies the maximum total cached data size (KB) allowed in private segments in the Network Buffer Cache (NBC).
Value:
  • Default: 131072
  • Range: 0 to MAXSHORT
  • Type: Dynamic
Diagnosis:
N/A
Tuning
Because data cached in private segments will be pinned by the Network Buffer Cache, this option provides a control on the amount of pinned memory used for Network Buffer Cache in addition to the network buffers in global segments. When this limit is met, cache data in private segments may be flushed for new cache data so the total pinned memory size will not exceed the limit. When this option is set to 0, all cache in private segments will be flushed.
ndpqsize
Purpose:
Specifies the number of packets to hold waiting on completion of a Neighbor Discovery Protocol (NDP) entry (used by MTU Path Discovery).
Value:
  • Default: 50
  • Range: 1 to MAXSHORT
  • Type: Dynamic
Diagnosis:
N/A
Tuning
N/A
ndpt_down
Purpose:
Specifies the time, in half-seconds, to hold down a Neighbor Discovery Protocol (NDP) entry.
Value:
  • Default: 3 (1.5 seconds)
  • Range: 1 to MAXINT
  • Type: Dynamic
Diagnosis:
N/A
Tuning
N/A
ndpt_keep
Purpose:
Specifies the time, in half seconds, to keep a Neighbor Discovery Protocol (NDP) entry.
Value:
  • Default: 120 (60 seconds)
  • Range: 1 to MAXINT
  • Type: Dynamic
Diagnosis:
N/A
Tuning
N/A
ndp_mmaxtries
Purpose:
pecifies the maximum number of Multicast NDP packets to send.
Value:
  • Default: 3
  • Range: 0 to MAXINT
  • Type: Dynamic
Diagnosis:
N/A
Tuning
N/A
ndpt_probe
Purpose:
Specifies the time, in half-seconds, to delay before sending the first Neighbor Discovery Protocol (NDP) probe.
Value:
  • Default: 5 (2.5 seconds)
  • Range: 1 to MAXINT
  • Type: Dynamic
Diagnosis:
N/A
Tuning
N/A
ndpt_reachable
Purpose:
Specifies the time, in half-seconds, to test if a Neighbor Discovery Protocol (NDP) entry is still valid.
Value:
  • Default: 30 (15 seconds)
  • Range: 1 to MAXINT
  • Type: Dynamic
Diagnosis:
N/A
Tuning
N/A
ndpt_retrans
Purpose:
Specifies the time, in half-seconds, to wait before retransmitting a Neighbor Discovery Protocol (NDP) request.
Value:
  • Default: 1(half a second)
  • Range: 1 to MAXINT
  • Type: Dynamic
Diagnosis:
N/A
Tuning
N/A
ndpt_umaxtries
Purpose:
Specifies the maximum number of Unicast NDP packets to send.
Value:
  • Default: 3
  • Range: 0 to MAXINT
  • Type: Dynamic
Diagnosis:
N/A
Tuning
N/A
net_malloc_police
Purpose:
Specifies the size of the net_malloc and net_free trace buffers.
Value:
  • Default: 0
  • Range: 0 to MAXINT
  • Type: Dynamic
Diagnosis:
N/A
Tuning
If the value of this variable is non-zero, all net_malloc and net_free buffers will be traced in a kernel buffer and by system trace hook HKWD_NET_MALLOC. Additional error-checking will also be enabled. This includes checks for freeing a free buffer, alignment, and buffer overwrite. Enable this parameter only when investigating some network problem, because performance is affected negatively when turned on. The default value is zero (policing off). Values of net_malloc_police larger than 1024 will allocate that many items in the kernel buffer for tracing.
nonlocsrcroute
Purpose:
Tells the Internet Protocol that strictly source-routed packets may be addressed to hosts outside the local network.
Value:
  • Default: 0
  • Range: 0 or 1
  • Type: Dynamic
Diagnosis:
N/A
Tuning
A default value of 0 disallows addressing to outside hosts. The value of 1 allows packets to be addressed to outside hosts. Loosely source-routed packets are not affected by this parameter. This is a configuration decision with minimal performance consequences.
passive_dgd
Purpose:
Specifies whether Passive Dead Gateway Detection is enabled. A value of 0 turns it off, and a value of 1 enables it for all gateways in use.
Value:
  • Default: 0
  • Range: 0 or 1
  • Type: Dynamic
Diagnosis:
N/A
Tuning
N/A
pmtu_default_age
Purpose:
Specifies the default amount of time (in minutes) before the path MTU value for UDP paths is checked for a lower value.
Value:
  • Default: 10
  • Range: 0 to MAXINT
  • Type: Dynamic
Diagnosis:
N/A
Tuning
A value of zero allows no aging. The default value is 10 minutes. The pmtu_default_age value can be overridden by UDP applications. This parameter only applies to AIX 4.2.1 or later.
pmtu_rediscover_interval
Purpose:
Specifies the default amount of time (in minutes) before the path MTU value for UDP and TCP paths are checked for a higher value.
Value:
  • Default: 30
  • Range: 0 to MAXINT
  • Type: Dynamic
Diagnosis:
N/A
Tuning
A value of 0 allows no path MTU rediscovery. The default value is 30 minutes. This parameter only applies to AIX 4.2.1 or later.
rfc1122addrchk
Purpose:
Performs address validation as specified by RFC1122 (Requirements for Internet Hosts-Communication Layers).
Value:
  • Default: 0(off)
  • Range: 0 or 1
  • Type: Dynamic
Diagnosis:
N/A
Tuning
The default value of 0 does not perform address validation. A value of 1 performs address validation.
rfc1323
Purpose:
Enables TCP enhancements as specified by RFC 1323 (TCP Extensions for High Performance). Value of 1 indicates that tcp_sendspace and tcp_recvspace can exceed 64 KB.
Value:
  • Default: 0(off)
  • Range: 0 or 1
  • Type: Dynamic
Diagnosis:
N/A
Tuning
The default value of 0 disables the RFC enhancements on a systemwide scale. A value of 1 specifies that all TCP connections will attempt to negotiate the RFC enhancements. The SOCKETS application can override the default behavior on individual TCP connections, using the setsockopt subroutine. Make changes before attempting to set tcp_sendspace and tcp_recvspace to more than 64 KB.
Refer to:
TCP Socket Buffer Tuning
rfc2414
Purpose:
Enables the increasing of TCP's initial window as described in RFC 2414. When it is on, the initial window will depend on the setting of the tunable tcp_init_window.
Value:
  • Default: 0 (off)
  • Range: 0 or 1 (on)
  • Type: Dynamic
Diagnosis:
N/A
Tuning
N/A
route_expire
Purpose:
Specifies whether the route expires.
Value:
  • Default: 0(off)
  • Range: 0 or 1
  • Type: Dynamic
Diagnosis:
N/A
Tuning
A value of 0 allows no route expiration, which is the default. Negative values are not allowed for this option. This parameter only applies to Version 4.2.1 or later.
Refer to:
Tuning TCP Maximum Segment Size
routerevalidate
Purpose:
Specifies that each connection's cached route should be revalidated each time a new route is added to the routing table. This will ensure that applications that keep the same connection open for long periods of time (for example, NFS) use the correct route after routing-table changes occur.
Value:
  • Default: 0(off)
  • Range: 0 or 1
  • Type: Dynamic
Diagnosis:
If there is communication loss between HACMP nodes or between NFS client and server, routes may have been changed but the values in the cache are being used.
Tuning
The default value of 0 does not revalidate the cached routes. Turning on this option may cause some performance degradation. Value should be set to 1 for HACMP.
rto_high
Purpose:
Specifies the TCP Retransmit timeout high value used in calculating factors and the maximum retransmittals allowable used in TCP data segment retransmittals.
Value:
  • Default: 64
  • Range: 2 to MAXINT
  • Type: Dynamic
Diagnosis:
N/A
Tuning
The rto_high parameter is the high factor.
rto_length
Purpose:
Specifies the TCP Retransmit timeout length value used in calculating factors and the maximum retransmittals allowable used in TCP data segment retransmittals.
Value:
  • Default: 13
  • Range: 2 to MAXINT
  • Type: Dynamic
Diagnosis:
N/A
Tuning
The rto_length parameter is the total number of time segments.
rto_limit
Purpose:
Specifies the TCP Retransmit timeout limit value used in calculating factors and the maximum retransmittals allowable used in TCP data segment retransmittals.
Value:
  • Default: 7
  • Range: 1 to 64
  • Type: Dynamic
Diagnosis:
N/A
Tuning
The rto_limit parameter is the number of time segments from rto_low to rto_high.
rto_low
Purpose:
Specifies the TCP Retransmit timeout low value used in calculating factors and the maximum retransmittals allowable used in TCP data segment retransmittals.
Value:
  • Default: 1
  • Range: 0 to 63
  • Type: Dynamic
Diagnosis:
N/A
Tuning
The rto_low parameter is the low factor.
sack (AIX 4.3.3 and later)
Purpose:
Specifies if Selective Acknowledgment is on.
Value:
  • Default: 0(off)
  • Range: 0 or 1
  • Type: Dynamic
Diagnosis:
N/A
Tuning
Normal TCP has to retransmit all packets after a dropped packet. With large window sizes, this can result in lost performance if many packets are dropped. Selective Ack enables code to selectively retransmit the lost packet(s). If there are a lot of retransmits of fragments and the receive buffer sizes are large, then it might be beneficial to turn this parameter on. This is a TCP negotiated option, so it must be supported on both endpoints before it will be used.
sb_max
Purpose:
Specifies the maximum buffer size allowed for a TCP and UDP socket. Limits setsockopt, udp_sendspace, udp_recvspace, tcp_sendspace, and tcp_recvspace.
Value:
  • Default: 1048576 bytes
  • Range: 1 to MAXINT
  • Type: Dynamic
Diagnosis:
N/A
Tuning
Increase size, preferably to multiple of 4096. Should be approximately two to four times the largest socket buffer limit.
Refer to:
TCP Socket Buffer Tuning and Tuning Other Layers to Improve NFS Performance
send_file_duration
Purpose:
Specifies the cache validation duration for all the file objects that the send_file system call accessed in the Network Buffer Cache (in seconds).
Value:
  • Default: 300 (5 minutes)
  • Range: 0 to MAXINT
  • Type: Dynamic


Diagnosis:
N/A
Tuning
A value of 0 means that the cache will be validated for every access. This parameter only applies to AIX 4.3.2 or later.
site6_index
Purpose:
Specifies the maximum interface number for site local routing.
Value:
  • Default: 0
  • Range: 0 to MAXSHORT
  • Type: Dynamic
Diagnosis:
N/A
Tuning
N/A
sockthresh
Purpose:
Specifies the maximum amount of network memory that can be allocated for sockets. Used to prevent new sockets or TCP connections from exhausting all MBUF memory and reserve the remaining memory for the existing sockets or TCP connections.
Value:
  • Default: 85 percent
  • Range: 0 to 100
  • Type: Dynamic
Diagnosis:
N/A
Tuning
When the total amount of memory allocated by the net_malloc subroutine reaches this threshold, the socket and socketpair system calls fail with an error of ENOBUFS. Incoming connection requests are silently discarded. Existing sockets can continue to use additional memory. The sockthresh parameter represents a percentage of the thewall parameter, with possible values of 1 to 100 and a default of 85.
Refer to:
Socket Layer
sodebug
Purpose:
Specifies whether the newly created sockets will have SO_DEBUG flag on.
Value:
  • Default: 0 (no)
  • Range: 0 or 1 (yes)
  • Type: Dynamic
Diagnosis:
N/A
Tuning
N/A
somaxconn
Purpose:
Specifies the maximum listen backlog.
Value:
  • Default: 1024 connections
  • Range: 0 to MAXSHORT
  • Type: Dynamic
Diagnosis:
N/A
Tuning
Increase this parameter on busy Web servers to handle peak connection rates.
subnetsarelocal
Purpose:
Specifies whether all subnets that match the subnet mask are to be considered local for purposes of establishing, for example, the TCP maximum segment size.
Value:
  • Default: 1(yes)
  • Range: 0 or 1
  • Type: Dynamic
Diagnosis:
N/A
Tuning
This parameter is used by the in_localaddress subroutine. The default value of 1 specifies that addresses that match the local network mask are local. If the value is 0, only addresses matching the local subnetwork are local. This is a configuration decision with performance consequences. If the subnets do not all have the same MTU, fragmentation at bridges may degrade performance. If the subnets do have the same MTU, and subnetsarelocal is 0, TCP sessions may use an unnecessarily small MSS.
Refer to:
Tuning TCP Maximum Segment Size
tcp_bad_port_limit
Purpose:
Specifies the number of TCP packets to a port with no socket that can be received in a 500 millisecond period before TCP stops sending resets in response to such packets. When it is set as its default value 0, resets will always be sent when TCP packets are received for a bad port number.
Value:
  • Default: 0
  • Range: 1 to MAXINT
  • Type: Dynamic
Diagnosis:
N/A
Tuning
N/A
tcp_ecn
Purpose:
Enables TCP level support for Explicit Congestion Notification as described in RFC 2481. Default is off (0). Turning it on (1) will make all connections negotiate ECN capability with the peer. For this feature to work you need support from the peer TCP and also IP level ECN support from the routers in the path.
Value:
  • Default: 0 (off)
  • Range: 0 or 1 (on)
  • Type: Dynamic
Diagnosis:
N/A
Tuning
N/A
tcp_ephemeral_high
Purpose:
Specifies the largest port number to allocate for TCP ephemeral ports.
Value:
  • Default: 65535
  • Range: 32769 to 65535
  • Type: Dynamic
Diagnosis:
N/A
Tuning
The number of ephemeral sockets is determined by tcp_ephemeral_high minus tcp_ephemeral_low. For maximum number of ephemeral sockets, set tcp_ephemeral_high to 65535 and tcp_ephemeral_low to 1024.
Refer to:
Socket Layer
tcp_ephemeral_low
Purpose:
Specifies the smallest port number to allocate for TCP ephemeral ports.
Value:
  • Default: 32768
  • Range: 1024 to 65534
  • Type: Dynamic
Diagnosis:
N/A
Tuning
The number of ephemeral sockets is determined by tcp_ephemeral_high minus tcp_ephemeral_low. For maximum number of ephemeral sockets, set tcp_ephemeral_high to 65535 and tcp_ephemeral_low to 1024.
Refer to:
Socket Layer
tcp_init_window
Purpose:
This value is used only when rfc2414 is turned on (ignored otherwise). If rfc2414 is on and this value is zero, then the initial window computation is done according to rfc2414. If this value is non-zero, the initial(congestion) window is initialized a number of maximum sized segments equal to tcp_init_window.
Value:
  • Default: 0
  • Range: 0 to MAXSHORT
  • Type: Dynamic
Diagnosis:
N/A
Tuning
N/A
tcp_keepcnt
Purpose:
Represents the number of keepalive probes that could be sent before terminating the connection.
Value:
  • Default: 8
  • Range: 0 to MAXINT
  • Type: Dynamic
Diagnosis:
N/A
Tuning
tcp_keepidle
Purpose:
Specifies the length of time to keep an idle TCP connection active, measured in half-seconds.
Value:
  • Default: 14400 (2 hours)
  • Range: 1 to MAXINT
  • Type: Dynamic
Diagnosis:
N/A
Tuning
This is a configuration decision with minimal performance consequences. No change is recommended.
tcp_keepinit
Purpose:
Sets the initial timeout value for a TCP connection in half-seconds.
Value:
  • Default: 150 (75 seconds)
  • Range: 1 to MAXINT
  • Type: Dynamic
Diagnosis:
N/A
Tuning
N/A
tcp_keepintvl
Purpose:
Specifies the interval, measured in half-seconds, between packets sent to validate the TCP connection.
Value:
  • Default: 150 (75 seconds)
  • Range: 1 to MAXSHORT
  • Type: Dynamic
Diagnosis:
N/A
Tuning
This is a configuration decision with minimal performance consequences. No change is recommended. If the interval were shortened significantly, processing and bandwidth costs might become significant.
tcp_limited_transmit
Purpose:
Enables the feature that enhances TCP's loss recovery as described in the RFC 3042.
Value:
  • Default: 1 (on)
  • Range: 0 or 1
  • Type: Dynamic
Diagnosis:
N/A
Tuning
N/A
tcp_maxburst
Purpose:
Specifies the number of back-to-back packets that TCP can send before pausing to allow those packets to be forwarded to their destination. This can be useful if routers are unable to handle large bursts of TCP packets and are dropping some of them. A value of 0 means no limitation for back-to-back packets before pausing.
Value:
  • Default: 0
  • Range: 0 to MAXSHORT
  • Type: Dynamic
Diagnosis:
N/A
Tuning
N/A
tcp_mssdflt
Purpose:
Default maximum segment size used in communicating with remote networks.
Value:
  • Default: 512 bytes
  • Range: 1 to 1448
  • Type: Dynamic
Diagnosis:
N/A
Tuning
For AIX 4.2.1 or later, tcp_mssdflt is only used if path MTU discovery is not enabled or path MTU discovery fails to discover a path MTU. Limiting data to (MTU - 52) bytes ensures that, where possible, only full packets will be sent.
Refer to:
Tuning TCP Maximum Segment Size
tcp_nagle_limit
Purpose:
This is the Nagle Algorithm threshold in bytes which can be used to disable Nagle. The default (65535 - the maximum size of IP packet) is Nagle turned on. To disable Nagle, set this value to 0 or 1. TCP disables Nagle for data segments larger than or equal to this threshold value.
Value:
  • Default: 65535 - maximum size of IP packet
  • Range: 0 to 65535
  • Type: Dynamic
Diagnosis:
N/A
Tuning
N/A
tcp_ndebug
Purpose:
Specifies the number of tcp_debug structures.
Value:
  • Default: 100
  • Range: 0 to MAXSHORT
  • Type: Dynamic
Diagnosis:
N/A
Tuning
N/A
tcp_newreno
Purpose:
Enables the modification to TCP's Fast Recovery algorithm as described in RFC 2582. This fixes the limitation of TCP's Fast Retransmit algorithm to recover fast from dropped packets when multiple packets in a window are dropped. sack also achieves the same thing but sack needs support from both ends of the TCP connection; the NewReno modification is only on the sender side.
Value:
  • Default: 1 (on)
  • Range: 0 or 1
  • Type: Dynamic
Diagnosis:
N/A
Tuning
N/A
tcp_nodelayack
Purpose:
Specifies that sockets using TCP follow the Nagle algorithm when sending data.
Value:
  • Default: 0(no)
  • Range: 0 or 1
  • Type: Dynamic
Diagnosis:
N/A
Tuning
This is an Interface-Specific Network Option (ISNO) option.
Refer to:
Relative Level of Function in UDP and TCP and Interface-Specific Network Options (ISNO)
tcp_pmtu_discover
Purpose:
Enables or disables path MTU discovery for TCP applications.
Value:
  • Default: 0 (1 in AIX 4.3.3)
  • Range: 0 or 1
  • Type: Dynamic
Diagnosis:
N/A
Tuning
A value of 0 disables path MTU discovery for TCP applications, while a value of 1 enables it. This parameter only applies to AIX 4.2.1 or later.
Refer to:
Tuning TCP Maximum Segment Size
tcp_recvspace
Purpose:
Specifies the system default socket buffer size for receiving data. This affects the window size used by TCP.
Value:
  • Default: 16384 bytes
  • Range: 4096 to 1048576
  • Type: Dynamic
Diagnosis:
N/A
Tuning
Setting the socket buffer size to 16 KB (16,384) improves performance over standard Ethernet and Token-Ring networks. Lower bandwidth networks, such as Serial Line Internet Protocol (SLIP), or higher bandwidth networks, such as Serial Optical Link, should have different optimum buffer sizes. The optimum buffer size is the product of the media bandwidth and the average round-trip time of a packet. The tcp_recvspace parameter must specify a socket buffer size less than or equal to the setting of the sb_max parameter. This is a Dynamic parameter, but for daemons started by the inetd daemon, run the following commands: stopsrc -s inetd ; startsrc -s inetd
Refer to:
TCP Socket Buffer Tuning
tcp_sendspace
Purpose:
Specifies the system default socket buffer size for sending data.
Value:
  • Default: 16384 bytes
  • Range: 4096 to 1048576
  • Type: Dynamic


Diagnosis:
N/A
Tuning
This affects the window size used by TCP. Setting the socket buffer size to 16 KB (16,384) improves performance over standard Ethernet and Token-Ring networks.

Lower bandwidth networks, such as Serial Line Internet Protocol (SLIP), or higher bandwidth networks, such as Serial Optical Link, should have different optimum buffer sizes. The optimum buffer size is the product of the media bandwidth and the average round-trip time of a packet:

optimum_window=bandwidth * average_round_trip_time

The tcp_sendspace parameter must specify a socket buffer size less than or equal to the setting of the sb_max parameter. The tcp_sendspace parameter is a Dynamic parameter, but for daemons started by the inetd daemon, run the following commands:

stopsrc -s inetd ; startsrc -s inetd
Refer to:
TCP Socket Buffer Tuning
tcp_timewait
Purpose:
The tcp_timewait option is used to configure how long connections are kept in the timewait state in 15-second intervals.
Value:
  • Default: 1
  • Range: 1 to 5
  • Type: Dynamic
Diagnosis:
N/A
Tuning
Increasing this value will degrade performance of Web servers or applications that open and close a lot of TCP connections.
tcp_ttl
Purpose:
Specifies the time to live for TCP packets.
Value:
  • Default: 60 ticks (100 ticks per minute)
  • Range: 1 to 255
  • Type: Dynamic
Diagnosis:
netstat -s
Tuning
If the system is experiencing TCP timeouts, increasing tcp_ttl may reduce retransmissions.
thewall
Purpose:
Specifies the maximum amount of memory, in kilobytes, that is allocated to the memory pool.
Value:
  • Default: AIX 5.1 and later: 1/2 of RAM or 6.5 GB (whichever is smaller)
  • Range: N/A
  • Type: Static
Diagnosis:
N/A
Tuning
Not settable from AIX 5.1 and later.
Refer to:
Tuning mbuf Pool Performance
udp_bad_port_limit
Purpose:
Specifies the number of UDP packets to a port with no socket that can be received in a 500 millisecond period before UDP stops sending ICMP errors in response to such packets. If set to 0, ICMP errors will always be sent when UDP packets are received for a bad port number. If greater than 0, it specifies the number of packets to be received before UDP stops sending ICMP errors.
Value:
  • Default: 0
  • Range: 0 to MAXINT
  • Type: Dynamic
Diagnosis:
N/A
Tuning
N/A
udp_ephemeral_high
Purpose:
Specifies the largest port number to allocate for UDP ephemeral ports.
Value:
  • Default: 65535
  • Range: 32769 to 65535
  • Type: Dynamic
Diagnosis:
N/A
Tuning
N/A
Refer to:
Socket Layer
udp_ephemeral_low
Purpose:
Specifies the smallest port number to allocate for UDP ephemeral ports.
Value:
  • Default: 32768
  • Range: 1 to 65534
  • Type: Dynamic
Diagnosis:
N/A
Tuning
N/A
Refer to:
Socket Layer
udp_pmtu_discover
Purpose:
Enables or disables path MTU discovery for UDP applications.
Value:
  • Default: 0 (1 in AIX 4.3.3)
  • Range: 0 or 1
  • Type: Dynamic
Diagnosis:
N/A
Tuning
UDP applications must be specifically written to use path MTU discovery. A value of 0 disables the feature, while a value of 1 enables it. The default value is 0. This parameter only applies to AIX 4.2.1 or later.
udp_recvspace
Purpose:
Specifies the system default socket-buffer size for receiving UDP data.
Value:
  • Default: 42080 bytes
  • Range: 4096 to 1048576
  • Type: Dynamic
Diagnosis:
Nonzero n in netstat -s report of udp: n socket buffer overflows
Tuning
The udp_recvspace parameter must specify a socket buffer size less than or equal to the setting of the sb_max parameter. Increase size, preferably to multiple of 4096.
Refer to:
UDP Socket Buffer Tuning
udp_sendspace
Purpose:
Specifies the system default socket-buffer size for sending UDP data.
Value:
  • Default: 9216 bytes
  • Range: 4096 to 1048576
  • Type: Dynamic
Diagnosis:
N/A
Tuning
The udp_sendspace parameter must specify a socket buffer size less than or equal to the setting of the sb_max parameter. Increase size, preferably to multiple of 4096.
Refer to:
UDP Socket Buffer Tuning
udp_ttl
Purpose:
Specifies the time to live for UDP packets.
Value:
  • Default: 30 second
  • Range: 1 to 255
  • Type: Dynamic
Diagnosis:
N/A
Tuning
N/A
udpcksum
Purpose:
Allows UDP checksum to be turned on/off.
Value:
  • Default: 1
  • Range: 0 or 1
  • Type: Dynamic
Diagnosis:
N/A
Tuning
A value of 0 turns it off; while a value of 1 turns it on.
use_isno (AIX 4.3.3 and later)
Purpose:
Allows per interface tuning options.
Value:
  • Default: 1(on)
  • Range: 0 or 1
  • Type: Dynamic
Diagnosis:
N/A
Tuning
A value of 1 means it is on, 0 is off. If the TCP tunable parameters per interface (tunable through SMIT or the chdev command) have been set, they will override the TCP global values if use_isno is set to 1. Application can still override all of these with the setsockopt subroutine.
Refer to:
Interface-Specific Network Options (ISNO)

Streams Tunable Parameters (AIX 4.2 or later)

lowthresh
Purpose:
Specifies the maximum number of bytes that can be allocated using the allocb call for the BPRI_LO priority.
Value:
  • Default: 90 (percent of thewall)
  • Range: 0 to 100
  • Type: Dynamic
Diagnosis:
N/A
Tuning
When the total amount of memory allocated by the net_malloc call reaches this threshold, then the allocb request for the BPRI_LO priority returns 0. The lowthresh parameter represents a percentage of the thewall parameter, and you can set its value from 0 to 100.
medthresh
Purpose:
Specifies the maximum number of bytes that can be allocated using the allocb() call for the BPRI_MED priority.
Value:
  • Default: 95 (percent of thewall)
  • Range: 0 to 100
  • Type: Dynamic
Diagnosis:
N/A
Tuning
When the total amount of memory allocated by the net_malloc call reaches this threshold, then the allocb request for the BPRI_MED priority returns 0. The medthresh parameter represents a percentage of the thewall parameter, and you can set its value from 0 to 100.
nstrpush
Purpose:
Specifies the maximum number (should be at least 8) of modules that you can push onto a single stream.
Value:
  • Default: 8
  • Range: 8 to MAXSHORT
  • Type: Dynamic
Diagnosis:
N/A
Tuning
N/A
psebufcalls
Purpose:
Specifies the maximum number of bufcalls to allocate by streams.
Value:
  • Default: 20
  • Range: 20 to MAXINT
  • Type: Dynamic
Diagnosis:
N/A
Tuning
The stream subsystem allocates certain number of bufcall structures at initialization. When the allocb call fails, the user can register their requests for the bufcall call. You cannot lower this value until the system reboots, at which time it returns to its default value.
psecache
Purpose:
Controls the number of stream buffers.
Value:
  • Default: 1
  • Range: 0 or 1
  • Type: Dynamic
Diagnosis:
N/A
Tuning
N/A
pseintrstack
Purpose:
Specifies the maximum size of the interrupt stack allowed by streams while running in the offlevel.
Value:
  • Default: 0x3000 (decimal 12288)
  • Range: 12288 to MAXINT
  • Type: Reboot
Diagnosis:
N/A
Tuning
When a process running other than INTBASE level enters into a stream, it occasionally encounters a stack overflow problem because the interrupt stack size is too small. Setting this parameter correctly reduces the chances of stack overflow problems.
psetimers
Purpose:
Specifies the maximum number of timers to allocate by streams.
Value:
  • Default: 20
  • Range: 20 to MAXINT
  • Type: Dynamic
Diagnosis:
N/A
Tuning
The stream subsystem allocates a certain number of timer structures at initialization, so that the streams driver or module can register their timeout calls. You cannot lower this value until the system reboots, at which time it returns to its default value.
strctlsz
Purpose:
Specifies the maximum number of bytes of information that a single system call can pass to a stream to place into the control part of a message (in an M_PROTO or M_PCPROTO block).
Value:
  • Default: 1024
  • Range: 1 to MAXSHORT
  • Type: Dynamic
Diagnosis:
N/A
Tuning
A putmsg call with a control part exceeding this size will fail with ERANGE.
strmsgsz
Purpose:
Specifies the maximum number of bytes of information that a single system call can pass to a stream to place into the data part of a message (in M_DATA blocks).
Value:
  • Default: 0
  • Range: 1 to MAXSHORT
  • Type: Dynamic
Diagnosis:
N/A
Tuning
Any write call exceeding this size is broken into multiple messages. A putmsg call with a data part exceeding this size will fail with ERANGE.
strthresh
Purpose:
Specifies the maximum number of bytes that streams are normally allowed to allocate, expressed as a percentage of thewall.
Value:
  • Default: depends on thewall
  • Range: 0 to 100
  • Type: Dynamic
Diagnosis:
N/A
Tuning
When the threshold is exceeded, it does not allow users without the appropriate privilege to open streams, push modules, or write to streams devices, and returns ENOSR. The threshold applies only to output side and does not affect data coming into the system (for example, the console continues to work correctly). A value of zero means that there is no threshold. The strthresh parameter represents a percentage of the thewall parameter, and you can set its value from 0 to 100. The thewall parameter indicates the maximum number of bytes that can be allocated by streams and sockets using the net_malloc call. When you change thewall parameter, the threshold is updated accordingly.
Refer to:
Tuning Network Memory
strturncnt
Purpose:
Specifies the maximum number of requests handled by the current running thread for Module- or Elsewhere-level streams synchronization.
Value:
  • Default: 15
  • Range: 1 to MAXINT
  • Type: Dynamic
Diagnosis:
N/A
Tuning
With Module-level synchronization, only one thread can run in the module at any time, and all other threads which try to acquire the same module will enqueue their requests and exit. After the current running thread completes its work, it dequeues all the previously enqueued requests one by one and invokes them. If there is a large number of requests enqueued in the list, then the current running thread has to serve everyone and will always be busy serving others and starves itself. To avoid this situation the current running thread serves only the strturncnt number of threads, following that, a separate kernel thread wakes up and invokes all the pending requests.

Examples

  1. To display the maximum size of the mbuf pool, type:

    no -o thewall
  2. To reset the time to live for UDP packets its default size, type:

    no -d udp_ttl
  3. To change the default socket buffer sizes on your system, type:

    no -r -o tcp_sendspace=32768
    no -r -o udp_recvspace=32768
  4. To use a machine as an internet work router over TCP/IP networks, type:

     no -o ipforwarding=1
  5. To list the current and reboot value, range, unit, type and dependencies of all tunables parameters managed by the no command, type:
    no -L
  6. To display help information on udp_ephemeral_high, type:
    no -h udp_ephemeral_high
  7. To permanently turn off ip6srcrouteforward, type:
    no -p -o ip6srcrouteforward=0
  8. To list the reboot values for all Network tuning parameters, type:
    no -r -a

Related Information

The ifconfig command, the inetd command, the vmo command, the ioo command, the schedo command, the tunsave command, the tunrestore command, the tuncheck command, the tundefault command.

The setsockopt subroutine.

Network Overview for System Management in AIX 5L Version 5.2 System Management Guide: Communications and Networks.

TCP/IP Addressing, TCP/IP Protocols, and TCP/IP Routing, Internet Protocol (IP), Transmission Control Protocol (TCP), Internet Application-Level Protocols, and User Datagram Protocol (UDP) in AIX 5L Version 5.2 System Management Guide: Communications and Networks.

Monitoring and Tuning Communications I/O Use in AIX 5L Version 5.2 Performance Management Guide.

Path MTU Discovery in AIX 5L Version 5.2 System Management Guide: Communications and Networks.

Kernel Tuning in AIX 5L Version 5.2 Performance Tools Guide and Reference.

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