Configures network attributes.
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. For a more information on how the network attributes interact with each other, refer to the AIX Version 4.3 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 rop of /etc/rc.net. If your system uses Berkeley-style network configuration, set the attributes near the top of /etc/rc.bsdnet.
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 Version 4.1.5, 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:
| ||||||||
| 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.. | ||||||||
| 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. | ||||||||
| 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 unoptomized 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 Version 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 Version 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 Version 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 Version 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. ipsendredirects is a runtime attribute. | ||||||||
| multi_homed | Specifies the level of multi-homed ipv6 host support.
| ||||||||
| 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 Version 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 Version 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 Version 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 Version 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 Version 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_police larger 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. | ||||||||
| 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 Version 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 Version 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 Version 4.3.3 and later versions, the rfc1323 network option can also be set on a per interface basis via the ifconfig command. | ||||||||
| 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 Version 4.2.1 or later. route_expire is a runtime attribute. In AIX Version 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. | ||||||||
| 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 Version 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 Version 4.3.1 or later. | ||||||||
| somaxconn | Specifies the maximum listen backlog. The default is 1024 bytes. somaxconn is a runtime attribute. This attribute only applies to AIX Version 4.1.5, 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_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_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_mssdflt | Default maximum segment size used in communicating with remote networks. For AIX Version 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 Version 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_ndebug | Specifies the number of tcp_debug structures. The default is 100. tcp_ndebug is 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 Version 4.2.1 or later. tcp_pmtu_discover is a runtime attribute. In AIX Version 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 Version 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 Version 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 Version 4.2.1 and earlier, the default value is 1/8 of real memory or 65536 (64 megabytes), whichever is smaller. In AIX Version 4.3, the default value is 1/8 of real memory or 131072 (128 megabytes), whichever is smaller. In AIX Version 4.3.1, the default value is 1/2 of real memory or 131072 (128 megabytes), whichever is smaller. In AIX Version 4.3.2 and later, the default value is 1/2 of real memory or 1048576 (1 gigabyte), whichever is smaller. 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 Version 4.2.1 or later. udp_pmtu_discover is a runtime attribute. In versions prior to AIX Version 4.3.3, the default value is 0 (disabled); in AIX Version 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 Version 4.3.3 and later versions. |
The following Streams Tunable atrributes only apply to AIX Version 4.2 or later.
no -o thewall=3072
no -d thewall
/usr/sbin/no -o tcp_sendspace=16384 /usr/sbin/no -o udp_recvspace=16384
no -o ipforwarding=1
Network Overview for System Management in AIX Version 4.3 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 Version 4.3 System Management Guide: Communications and Networks.
Monitoring and Tuning Communications I/O in AIX Versions 3.2 and 4 Performance Tuning Guide.
Path MTU Discovery in AIX Version 4.3 System Management Guide: Communications and Networks.