Commands Reference, Volume 4

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.

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.

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

• 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

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

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

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

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

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

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.

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.

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 {}.

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

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

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

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.

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.

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.

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

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.

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

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

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.

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

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

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.

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

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.

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.

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.

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.

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

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

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.

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.

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

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

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

Purpose:

Specifies the maximum number of IPv6 packet-reassembly queues.

Value:

• Range: 1 to MAXSHORT
• Type: Dynamic

Diagnosis:

N/A

Tuning

N/A

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

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.

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.

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.

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

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.

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.

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

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

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

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

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

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

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

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

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.

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.

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

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.

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.

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.

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

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

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

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.

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.

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.

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.

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.

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.

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

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.

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

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

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

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.

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

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

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

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

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

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

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

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.

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

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.

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

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

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

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

Purpose:

Specifies the number of tcp_debug structures.

Value:

• Default: 100
• Range: 0 to MAXSHORT
• Type: Dynamic

Diagnosis:

N/A

Tuning

N/A

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

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)

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

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

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

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.

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.

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

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

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

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

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.

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

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

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

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.

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)

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.

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.

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

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.

Purpose:

Controls the number of stream buffers.

Value:

• Default: 1
• Range: 0 or 1
• Type: Dynamic

Diagnosis:

N/A

Tuning

N/A

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.

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.

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.

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.

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

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.