Commands Reference, Volume 4

no Command

Syntax

no { -a | -d Attribute | -o Attribute [ =NewValue ] }

Use the no command to configure network attributes. The no command sets or displays current network attributes in the kernel. This command only operates on the currently running kernel. The command must be run again after each startup or after the network has been configured. Whether the command sets or displays an attribute is determined by the accompanying flag. The -o flag performs both actions. It can either display the value of an attribute or set a new value for an attribute. When the no command is used to modify a network option it will log a message to the syslog using the LOG_KERN facility. For a more information on how the network attributes interact with each other, refer to the AIX 5L Version 5.1 System Management Guide: Communications and Networks.

Attention: Be careful when you use this command. The no command performs no range checking, therefore it accepts all values for the variables. If used incorrectly, the no command can cause your system to become inoperable.

Some network attributes are runtime attributes that can be changed at any time. Others are loadtime attributes that must be set before the netinet kernel extension is loaded and be placed near the top of /etc/rc.net. If your system uses Berkeley-style network configuration, set the attributes near the top of /etc/rc.bsdnet.

Flags

-a

Prints a list of all configurable attributes and their current values.

-d Attribute

Sets Attribute back to its default value.

-o Attribute [=NewValue ]

Displays the value of Attribute if NewValue is not specified else sets Attribute to NewValue.

Note: When using the -o flag do not enter space characters before or after the equal sign. If you do, the command will fail.

Attributes

You can set the following attributes:

arpqsize	Specifies the maximum number of packets to queue while waiting for ARP responses. Default value is 1. This attribute 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 attribute applies to AIX 4.1.5, AIX 4.2.1, and later. arpqsize is a runtime attribute.
arptab_bsiz	Specifies Address Resolution Protocol (ARP) table bucket size. The default value is 7. arptab_bsiz is a loadtime attribute.
arptab_nb	Specifies the number of ARP table buckets. The default value is 25. arptab_nb is a loadtime attribute.
arpt_killc	Specifies the time in minutes before a complete ARP entry will be deleted. The default value is 20 minutes. arpt_killc is a runtime attribute.
bcastping	Allows response to ICMP echo packets to the broadcast address. A value of 0 turn it off; while a value on 1 turns it on. Default is 0. bcastping is a runtime attribute.
clean_partial_conns	Specifies whether or not we are avoiding SYN attacks. If non-zero, clean_partial_conns specifies how many partial connections to randomly remove to make room for new non-attack connections. This is a runtime attribute. The default is 0, off.
delayack	Delays ACKs for certain TCP packets and attempts to piggyback them with the next packet sent instead. This will only be performed for connections whose destination port is specified in the list of the delayackports attribute. This can be used to increase performance when communicating with an HTTP server. This attribute is available only in AIX 4.3.2 and beyond. The attribute can have one of four values: 0 No delays; normal operation 1 Delay the ACK for the server's SYN 2 Delay the ACK for the server's FIN 3 Delay both the ACKs for the SYN and FIN
delayackports	Specifies the list of destination ports for which the operation defined by the delayack port option will be performed. The attribute 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 {} This attribute is available only in AIX 4.3.2 and beyond.
dgd_packets_lost	Specifies how many consecutive packets must be lost before Dead Gateway Detection decides that a gateway is down. The default value is 3. This attribute applies to AIX 5.1 and later.
dgd_ping_time	Specifies how many seconds should pass between pings of a gateway by Active Dead Gateway Detection. The default value is 5. This attribute applies to AIX 5.1 and later.
dgd_retry_time	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. The default value is 5. This attribute applies to AIX 5.1 and later.
directed_broadcast	Specifies whether or not to allow a directed broadcast to a gateway. 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. directed_broadcast is a runtime attribute.
extendednetstats	Enables more extensive statistics for network memory services. The default for this attribute is 1. However, because these extra statistics cause a reduction in system performance, extendednetstats is set to 0, for off, in /etc/rc.net. If these statistics are desired, it is recommended that the code in /etc/rc.net that sets extendednetstats to 0 be commented out. This attribute is available only in AIX 4.3.2 and beyond.
fasttimo	Allows you to set the millisecond delay for the TCP fast timeout timer. Its range is 50 to 200 milliseconds. 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	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.
icmpaddressmask	Specifies whether the system responds to an ICMP address mask request. If the default value 0 is set, the network silently ignores any ICMP address mask request that it receives. icmpaddressmask is a runtime attribute.
ie5_old_multicast_mapping	Specifies IP multicasts on token ring should be mapped to the broadcast address rather than a functional address when value 1 is used. The default value is 0. ie5_old_multicast_mapping is a runtime attribute.
ifsize	Specifies the maximum number of network interface structures per interface. The default value is 8. In AIX 4.3.2 and above, if the system detects at boot time that more adapters of a type are present than would be allowed by the current value of ifsize, it will automatically increase the value to support the number of adapters present. ifsize is a loadtime attribute.
inet_stack_size	Lets you configure the inet interrupt stack table size. This is needed if you were running with unoptimized debug kernel and/or netinet. It must be set in rc.net; changing it on the fly has no effect. This is different from the pin more stack code because this is on interrupt. The pin more stack code is not configurable. inet_stack_size is specified in KB, the default is 16 KB.
ipforwarding	Specifies whether the kernel should forward packets. The default value of 0 prevents forwarding of IP packets when they are not for the local system. A value of 1 enables forwarding. ipforwarding is a runtime attribute.
ipfragttl	Specifies the time to live for IP fragments. The default value is 60 half-seconds. ipfragttl is a runtime attribute.
ipignoreredirects	Specifies whether or not to process redirects that are received. The default value of 0 processes redirects as usual. A value of 1 ignores redirects. This option only applies to AIX 4.2.1 or later. ipignoreredirects is a runtime attribute.
ipqmaxlen	Specifies the number of received packets that can be queued on the IP protocol input queue. ipqmaxlen is a loadtime attribute.
ipsendredirects	Specifies whether the kernel should send redirect signals. The default value of 1 sends redirects. A value of 0 does not send redirects. ipsendredirects is a runtime attribute.
ipsrcrouteforward	Specifies whether the system forwards source routed packets. 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 attribute only applies to AIX 4.2.1 or later.
ipsrcrouterecv	Specifies whether the system accepts source routed packets. 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 attribute only applies to AIX 4.2.1 or later.
ipsrcroutesend	Specifies whether applications can send source routed packets. 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 attribute only applies to AIX 4.2.1 or later.
ip6_defttl	Specifies the default hop count that is used for IPv6 packets if no other hop count is specified.
ip6forwarding	Specifies whether the kernel should forward ipv6 packets. The default value of 0 prevents forwarding of ipv6 packets when they are not for the local systems. A value of 1 enables forwarding. This is a runtime attribute.
ip6_prune	Specifies how often to check the IPv6 routing table for expired routes. The default is 2 seconds.
ip6srcrouteforward	Specifies whether the system forwards source-routed IPv6 packets. 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.
main_if6	Specifies the interface to use for link local addresses. This is only used by autoconf6 to setup initial routes.
main_site6	Specifies the interface to use for site local address routing. This is only used if multi_homed is set to 3.
maxnip6q	Specifies the maximum number of ipv6 packet reassembly queues. The default is 20.
maxttl	Specifies the time to live for RIP packets. The default is 255 seconds. ipsendredirectsis a runtime attribute.
multi_homed	Specifies the level of multi-homed ipv6 host support. 0 Indicates the original functionality in AIX 4.3. 1 Indicates that link local addresses will be a 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	Specifies the total maximum amount of memory that can be used for the Network Buffer Cache. This attribute is in number of KBytes. The default value is derived from thewall. When the cache grows to this limit, the least-used cache objects are flushed out of cache to make room for the new ones. This attribute only applies to AIX 4.3.2 or later.
nbc_max_cache	Specifies the maximum size of the cache object allowed in the Network Buffer Cache without using the private segments. This parameter is in number of bytes, the default being 131,072 (128K) bytes. A data object bigger than this size is either cached in a private segment or is not cached at all. This attribute only applies to AIX 4.3.2 or later.
nbc_min_cache	Specifies the minimum size of the cache object allowed in the Network Buffer Cache. This attribute is in number of bytes, the default being 1 byte. A data object smaller than this size is not put into the NBC. This attribute only applies to AIX 4.3.2 or later.
nbc_pseg	Specifies the maximum number of private segments that can be created for the Network Buffer Cache. The default value is 0. When this option is set at non-0, a data object between the size specified in nbc_max_cache and the segment size (256MB) is cached in a private segment. A data object bigger than the segment size is not cached at all. When the maximum number of private segments exist, cache data in private segments may be flushed for new cache data so that the number of private segments do not exceed the limit. When nbc_pseg is set to 0, all cache in private segments are flushed. This attribute only applies to AIX 4.3.3 or later.
nbc_pseg_limit	Specifies the maximum amount of cached data size allowed in private segments in the Network Buffer Cache. This value is expressed in KBytes. The default value is half of the total real memory size on the running system. Since data cached in private segments are pinned by the Network Buffer Cache, nbc_pseg_limit controls the amount of pinned memory used for the Network Buffer Cache in addition to the network buffers in global segments. When the amount of cached data reaches this limit, cache data in private segments may be flushed for new cache data so that the total pinned memory size doesn't exceed the limit. When nbc_pseg_limit is set to 0, all cache in private segments is flushed. This attribute only applies to AIX 4.3.3 or later.
ndpqsize	Specifies the number of packets to hold waiting on completion of a Neighbor Discovery Protocol (NDP) entry. The default is 50 packets.
ndpt_down	Specifies the time, in half seconds, to hold down a NDP entry. The default value is 3 units, or 1.5 seconds.
ndpt_keep	Specifies the time, in half seconds, to keep a NDP entry. The default value is 120 or 60 seconds.
ndpt_mmaxtries	Specifies the maximum number of Multicast NDP packets to send. The default is value is 3.
ndpt_probe	Specifies the time, in half seconds, to delay before sending their first NDP probe. The default value is 5 units, or a 2.5 seconds.
ndpt_reachable	Specifies the time, in half seconds, to test if a NDP entry is still valid. The default is 30, or 15 seconds.
ndpt_retrans	Specifies the time, in half seconds, to wait before retransmitting a NDP request. The default is 1, or a half second.
ndpt_umaxtries	Specifies the maximum number of Unicast NDP packets to send. The default is value is 3.
net_malloc_police	Specifies the size of the `net_malloc/net_free` trace buffer. If the value of this variable is non-zero all `net_malloc` and `net_free`'s 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. The default value is zero (policing off). Values of net_malloc_policelarger than 1024 will allocate that many items in the kernel buffer for tracing. net_malloc_police is a runtime attribute.
nonlocsrcroute	Tells the Internet Protocol that strictly source-routed packets may be addressed to hosts outside the local network. 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 attribute. nonlocsrcroute is a runtime attribute.
passive_dgd	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. The default value is 0. This attribute applies to AIX 5.1 and later.
pmtu_default_age	Specifies the default amount of time (in minutes) before the path MTU value for UDP paths is checked for a lower value. 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 attribute only applies to AIX 4.2.1 or later. pmtu_default_age is a runtime attribute.
pmtu_rediscover_interval	Specifies the default amount of time (in minutes) before the path MTU value for UDP and TCP paths are checked for a higher value. A value of 0 allows no path MTU rediscovery. The default value is 30 minutes. This attribute only applies to AIX 4.2.1 or later. pmtu_rediscover_interval is a runtime attribute.
rfc1122addrchk	Performs address validation as specified by RFC1122, Requirements for Internet Hosts-Communication Layers. The default value of 0 does not perform address validation. A value of 1 performs address validation. rfc1122addrchk is a runtime attribute.
rfc1323	Enables TCP enhancements as specified by RFC 1323, TCP Extensions for High Performance. The default value of 0 disables the RFC enhancements on a system-wide 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. rfc1323 is a runtime attribute. In AIX 4.3.3 and later versions, the rfc1323 network option can also be set on a per interface basis via the ifconfig command.
rfc2414	Enables the increasing of TCP's initial window as described in RFC 2414. The default is `off` (0). Set this to `1` to turn it on. When it is on, the initial window will depend on the setting of the tunable tcp_init_window. This feature was added in AIX 5.1.
route_expire	Specifies whether the route expires. A value of 0 allows no route expiration, which is the default. Negative values are not allowed for this option. This attribute only applies to AIX 4.2.1 or later. route_expire is a runtime attribute. In AIX 4.3.3 and later versions, the default value is 1.
routerevalidate	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) will use the correct route after routing table changes occur. The default value of 0 does not revalidate the cached routes. Turning this option on may cause some performance degradation. routerevalidate is a runtime attribute.
rto_length	Specifies the TCP Retransmit Time Out length value used in calculating factors and the maximum retransmits allowable used in TCP data segment retransmits. `rto_length` is the total number of time segments. Default is 13. rto_length is a loadtime attribute.
rto_limit	Specifies the TCP Retransmit Time out limit value used in calculating factors and the maximum retransmits allowable used in TCP data segment retransmits. `rto_limit` is the number of time segments from `rto_low` to `rto_high`. Default is 7. rto_limit is a loadtime attribute.
rto_low	Specifies the TCP Retransmit Time Out low value used in calculating factors and the maximum retransmits allowable used in TCP data segment retransmits. `rto_low` is the low factor. Default 1. rto_low is a loadtime attribute.
rto_high	Specifies the TCP Retransmit Time out high value used in calculating factors and the maximum retransmits allowable used in TCP data segment retransmits. `rto_high` is the high factor. Default is 64. rto_high is a loadtime attribute.
sb_max	Specifies the maximum buffer size allowed for a socket. The default is 65,536 bytes. sb_max is a run attribute.
sack	Enables TCP Selective Acknowledgement as described in RFC 2018. A value of `1` will make all TCP connections negotiate sack. Default is `zero` which disables the negotiation. sack feature needs support from the peer TCP. The negotiation phase during connection initiation determines that. When receiving out of order segments, `Selective Acknowledgements` from the receiver will inform the sender of data that has been received so that the sender can retransmit only the missing segments resulting in less unnecessarily retransmitted segments. sack is useful for recovering fast from multiple packet drops in a window of data. This option was added in AIX 4.3.3.
send_file_duration	Specifies the cache validation duration for all the file objects that system call send_file accessed in the Network Buffer Cache. This attribute is in number of seconds, the default is 300 for 5 minutes. 0 means that the cache will be validated for every access. This attribute only applies to AIX 4.3.2 or later.
site6_index	Specifies the maximum interface number for site local routing.
sockthresh	Specifies the maximum amount of network memory that can be allocated for sockets. 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 attribute represents a percentage of the thewall attribute, with possible values of 1 to 100 and a default of 85. sockthresh is a runtime attribute. This attribute only applies to AIX 4.3.1 or later.
sodebug	Specifies whether the newly created sockets will have SO_DEBUG flag on.
somaxconn	Specifies the maximum listen backlog. The default is 1024 bytes. somaxconn is a runtime attribute. This attribute only applies to AIX 4.1.5, AIX 4.2, or later.
subnetsarelocal	Determines if a packet address is on the local network. This attribute 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. subnetsarelocal is a runtime attribute.
tcp_ecn	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. This feature was added in AIX 5.1.
tcp_ephemeral_low	Specifies the smallest port number to allocate for TCP ephemeral ports. The default is 32768. This attribute is available only in AIX 4.3.1 and beyond.
tcp_ephemeral_high	Specifies the largest port number to allocate for TCP ephemeral ports. The default is 65535. This attribute is available only in AIX 4.3.1 and beyond.
tcp_init_window	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. This feature was added in AIX 5.1.
tcp_keepidle	Specifies the length of time to keep the connection active, measured in half seconds. The default is 14,400 half seconds (7200 seconds or 2 hours). tcp_keepidle is a runtime attribute.
tcp_keepinit	Sets the initial timeout value for a tcp connection. This value is defined in 1/2 second units, and defaults to 150, which is 75 seconds. It can be changed to any value with the -o flag. tcp_keepinit is a runtime attribute.
tcp_keepintvl	Specifies the interval, measured in half seconds, between packets sent to validate the connection. The default is 150 half seconds (75 seconds). tcp_keepintvl is a runtime attribute.
tcp_limited_transmit	Enables the feature that enhances TCP's loss recovery as described in the RFC 3042. The default is `on` (1). To turn it off set it to zero. This feature was added in AIX 5.1.
tcp_mssdflt	Default maximum segment size used in communicating with remote networks. 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 discovery a path MTU. tcp_mssdflt is a runtime attribute. The default value is 512. In AIX 4.3.3 and later versions, the tcp_mssdflt network option can also be set on a per interface basis via the ifconfig command.
tcp_nagle_limit	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.This feature was added in AIX 4.3.3.
tcp_newreno	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. This feature was added in AIX 4.3.3. In AIX 5.1 the default is `on` (1).
tcp_ndebug	Specifies the number of tcp_debug structures. The default is 100. tcp_ndebugis a runtime attribute.
tcp_pmtu_discover	Enables or disables path MTU discovery for TCP applications. A value of 0 disables path MTU discovery for TCP applications, while a value of 1 enables it. The default value is 0. This attribute only applies to AIX 4.2.1 or later. tcp_pmtu_discover is a runtime attribute. In AIX 4.3.3 and later versions, the default value is 1 (enabled).
tcp_recvspace	Specifies the system default socket buffer size for receiving data. This affects the window size used by TCP. Setting the socket buffer size to 16KB (16,384) improves performance over Standard Ethernet and token-ring networks. The default is a value of 4096; however, a value of 16,384 is set automatically by the rc.net file or the rc.bsdnet file (if Berkeley-style configuration is issued). 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. In AIX 4.3.3 and later versions, the tcp_recvspace network option can also be set on a per interface basis via the ifconfig command. The tcp_recvspace attribute must specify a socket buffer size less than or equal to the setting of the `sb_max` attribute. tcp_recvspace is a runtime attribute, but for daemons started by inetd, the following command needs to be executed: 'stopsrc -s inetd ; startsrc -s inetd'
tcp_sendspace	Specifies the system default socket buffer size for sending data. This affects the window size used by TCP. Setting the socket buffer size to 16KB (16,384) improves performance over Standard Ethernet and Token-Ring networks. The default is a value of 4096; however, a value of 16,384 is set automatically by the rc.net file or the rc.bsdnet file (if Berkeley-style configuration is issued). 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 In AIX 4.3.3 and later versions, the tcp_sendspace network option can also be set on a per interface basis via the ifconfig command. The `tcp_sendspace` attribute must specify a socket buffer size less than or equal to the setting of the `sb_max` attribute. tcp_sendspace is a runtime attribute, but for daemons started by inetd, the following command needs to be executed: 'stopsrc -s inetd ; startsrc -s inetd'
tcp_timewait	The tcp_timewait option is used to configure how long connections are kept in the timewait state. It is given in 15 second intervals, and the default is 1.
tcp_ttl	Specifies the time to live for TCP packets. The default is 60 ticks (100 ticks per minute). tcp_ttl is a runtime attribute.
thewall	Specifies the maximum amount of memory, in kilobytes, that is allocated to the memory pool. In AIX 4.2.1 and earlier, the default value is 1/8 of real memory or 65536 (64 megabytes), whichever is smaller. In AIX 4.3, the default value is 1/8 of real memory or 131072 (128 megabytes), whichever is smaller. In AIX 4.3.1, the default value is 1/2 of real memory or 131072 (128 megabytes), whichever is smaller. In AIX 4.3.2 and later, the default value depends on whether you are running on a CHRP machine or not. For non-CHRP machines, the default value is 1/2 of real memory or 262144 (256 megabytes), whichever is smaller. For CHRP machines, the default value is 1/2 of real memory or 1048576 (1 gigabyte). thewall is a runtime attribute.
udp_ephemeral_low	Specifies the smallest port number to allocate for UDP ephemeral ports. The default is 32768. This attribute is available only in AIX 4.3.1 and beyond.
udp_ephemeral_high	Specifies the largest port number to allocate for UDP ephemeral ports. The default is 65535. This attribute is available only in AIX 4.3.1 and beyond.
udp_pmtu_discover	Enables or disables path MTU discovery for UDP applications. UDP applications must be specifically written to utilize path MTU discovery. A value of 0 disables the feature, while a value of 1 enables it. This attribute only applies to AIX 4.2.1 or later. udp_pmtu_discover is a runtime attribute. In versions prior to AIX 4.3.3, the default value is 0 (disabled); in AIX 4.3.3 and later versions, the default value is 1 (enabled).
udp_recvspace	Specifies the system default socket buffer size for receiving UDP data. The default is 41,600 bytes. The `udp_recvspace` attribute must specify a socket buffer size less than or equal to the setting of the `sb_max` attribute. udp_recvspace is a runtime attribute.
udp_sendspace	Specifies the system default socket buffer size for sending UDP data. The default is 9216 bytes. The `udp_sendspace` attribute must specify a socket buffer size less than or equal to the setting of the `sb_max` attribute. udp_sendspace is a runtime attribute.
udp_ttl	Specifies the time to live for UDP packets. The default is 30 seconds. udp_ttl is a runtime attribute.
udpcksum	Allows UDP checksum to be turned on/off. A value of 0 turns it off; while a value of 1 turns it on. Default is 1. udpcksum is a runtime attribute. Note: If you use the `tcp_recvspace`, `tcp_sendspace`, `udp_recvspace` or `udp_sendspace` attribute to specify a socket to a buffer size larger than the `sb_max` attribute default, you must set the `sb_max` attribute to an equal or greater value. Otherwise, the socket system call returns the ENOBUFS error message when an application tries to create a socket.
use_isno	Enables the use of Interface Specific Network Options. The default value is 1 (enabled). This attribute only applies to AIX 4.3.3 and later versions.

Streams Tunable Attributes

The following Streams Tunable attributes only apply to AIX 4.2 or later.

lowthresh	Specifies the maximum number of bytes that can be allocated using the allocb call for the BPRI_LO priority. 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 attribute represents a percentage of the thewall attribute and you can set its value from 0 to 100. This is a runtime attribute and the default value is set to 90 (90% of thewall attribute).
medthresh	Specifies the maximum number of bytes that can be allocated using the allocb call for the BPRI_MED priority. 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 attribute represents a percentage of the thewall attribute and you can set its value from 0 to 100. This is a runtime attribute and the default value is set to 95 (95% of thewall attribute).
nstrpush	Specifies the maximum number (should be at least 8) of modules that you can push onto a single Stream. This is a loadtime attribute and the default value is set to 8.
psebufcalls	Specifies the maximum number of bufcalls to allocate by Streams. The Stream subsystem allocates certain number of bufcall structures at initialization, so that when the allocb call fails, the user can register their requests for the bufcall. You are not allowed to lower this value until the system reboots, at which time it returns to its default value. This is a runtime attribute and the default value is set to 20.
pseintrstack	Specifies the maximum size of the interrupt stack allowed by Streams while running in the offlevel. Sometimes, when a process running other than INTBASE level enters into a Stream, it encounters a stack overflow problem because the interrupt stack size is too small. Setting this attribute properly reduces the chances of stack overflow problems. This is a loadtime attribute and the default value is set to 0x3000.
psetimers	Specifies the maximum number of timers to allocate by Streams. The Stream subsystem allocates certain a number of timer structures at initialization, so that the streams driver or module can register their timeout calls. You are not allowed to lower this value until the system reboots, at which time it returns to its default value. This is a runtime attribute and the default value is set to 20.
strctlsz	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). A putmsg call with a control part exceeding this size will fail with ERANGE. This is a runtime attribute and the default value is set to 1024.
strmsgsz	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). 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. This is a runtime attribute and the default value is set to 1024.
strthresh	Specifies the maximum number of bytes Streams are normally allowed to allocate. When the threshold is passed, 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 (e.g. console continues to work properly). A value of zero means that there is no threshold. The strthresh attribute represents a percentage of the thewall attribute and you can set its value from 0 to 100. The thewall attribute indicates the maximum number of bytes that can be allocated by Streams and Sockets using the net_malloc call. When you change thewall attribute, the threshold gets updated accordingly.
strturncnt	Specifies the maximum number of requests handled by the current running thread for Module or Elsewhere level Streams synchronization.The Module level synchronization works in such a way that 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 leave. After the current running thread completes its work, it dequeues all the previously enqueued requests one by one and invokes them. If there are 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 the current running thread serves only the strturncnt number of threads, after that a separate kernel thread wakes up and invokes all the pending requests. This is a runtime attribute and the default value is set to 15.

Examples

To change the maximum size of the mbuf pool to 3MB, enter:
```
no -o thewall=3072
```
To reset the maximum size of the mbuf pool to its default size, enter:
```
no -d thewall
```
To change the default socket buffer sizes on your system, add the following lines to the end of the /etc/rc.net file:
```
/usr/sbin/no -o tcp_sendspace=16384
/usr/sbin/no -o udp_recvspace=16384
```
To use a machine as an internet work router over TCP/IP networks, enter:
```
 no -o ipforwarding=1
```

Related Information

Network Overview for System Management in AIX 5L Version 5.1 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 5.1 System Management Guide: Communications and Networks.

Monitoring and Tuning Communications I/O Use in AIX 5L Version 5.1 Performance Management Guide.

Path MTU Discovery in AIX 5L Version 5.1 System Management Guide: Communications and Networks.