The following paragraphs summarize the attributes and tuning techniques for each of the communications tuning parameters.
| Purpose: | Provide an absolute upper bound on the amount of real memory that can be used by the communication subsystem. |
| Values: | AIX 4.2.1 and earlier: Default: 1/8 of real memory. Range: up to 1/2 of real memory or 65536 (64 megabytes), whichever is smaller.
AIX 4.3.0: Default: 1/8 of real memory. Range: up to 1/2 of real memory or 131072 (128 megabytes), whichever is smaller. AIX 4.3.1: Default: 1/2 of real memory. Range: up to 1/2 of real memory or 131072 (128 megabytes), whichever is smaller. AIX 4.3.2: Default: 1/2 of real memory. Range: up to 1/2 of real memory or 1048576 (1 gigabyte), whichever is smaller. |
| Display: | no -a or no -o thewall |
| Change: | no -o thewall=newvalue
newvalue is in KB, not bytes Change takes effect immediately for new connections. Change is effective until the next system boot. |
| Diagnosis: | None. |
| Tuning: | Increase size, preferably to multiple of 4(KB). |
| Refer to: | mbuf Pool Performance Tuning. |
| Purpose: | In AIX Version 4.3.1 or later, provide a way to prevent new sockets from being created when almost all the network memory is in use. |
| Values: | Default: 85% of thewall. Range: 1-100 |
| Display: | no -a or no -o sockthresh |
| Change: | no -o sockthresh=newvalue
newvalue is a percentage of thewall. Change takes effect immediately. Change is effective until the next system boot. Note: Change will fail if the user attempts to set a new value that is less than the amount of memory currently in use. |
| Diagnosis: | None. |
| Tuning: | Decrease percentage. |
| Refer to: | Socket Layer. |
| Purpose: | Provide an absolute upper bound on the size of TCP and UDP socket buffers. Limits setsockopt(), udp_sendspace, udp_recvspace, tcp_sendspace, and tcp_recvspace. |
| Values: | Default: 65536 Range: N/A |
| Display: | no -a or no -o sb_max |
| Change: | no -o sb_max=newvalue
Change takes effect immediately for new connections. Change is effective until the next system boot. |
| Diagnosis: | None. |
| Tuning: | Increase size, preferably to multiple of 4096. Should be about twice the largest socket buffer limit. |
| Refer to: | Socket Layer. |
| Purpose: | Value of 1 indicates that tcp_sendspace and tcp_recvspace can exceed 64KB. |
| Values: | Default: 0 Range: 0 or 1 |
| Display: | no -a or no -o rfc1323 |
| Change: | no -o rfc1323=newvalue
Change takes effect immediately. Change is effective until the next system boot. |
| Diagnosis: | None. |
| Tuning: | Change before attempting to set tcp_sendspace and tcp_recvspace to more than 64KB. |
| Refer to: | TCP Layer. |
| Purpose: | Provide the default value for the size of the UDP socket send buffer. |
| Values: | Default: 9216 Range: 0 to 65536
Must be less than or equal to sb_max. |
| Display: | no -a or no -o udp_sendspace |
| Change: | no -o udp_sendspace=newvalue
Change takes effect immediately for new connections. Change is effective until the next system boot. |
| Diagnosis: | None. |
| Tuning: | Increase size, preferably to multiple of 4096. |
| Refer to: | Socket Layer. |
| Purpose: | Provide the default value of the size of the UDP socket receive buffer. |
| Values: | Default: 41600 Range: N/A
Must be less than or equal to sb_max. |
| Display: | no -a or no -o udp_recvspace |
| Change: | no -o udp_recvspace=newvalue
Change takes effect immediately for new connections. Change is effective until the next system boot. |
| Diagnosis: | Nonzero n in netstat -s report of udp: n socket buffer overflows |
| Tuning: | Increase size, preferably to multiple of 4096. |
| Refer to: | Socket Layer. |
| Purpose: | Provide the default value of the size of the TCP socket send buffer. |
| Values: | Default: 16384 Range: 0 to 64KB if rfc1323=0,
Range: 0 to 4GB if rfc1323=1. Must be less than or equal to sb_max. Should be equal to tcp_recvspace and uniform on all frequently accessed AIX systems. |
| Display: | no -a or no -o tcp_sendspace |
| Change: | no -o tcp_sendspace=newvalue
Change takes effect immediately for new connections. Change is effective until the next system boot. |
| Diagnosis: | Poor throughput. |
| Tuning: | Increase size, preferably to multiple of 4096. |
| Refer to: | Socket Layer. |
| Purpose: | Provide the default value of the size of the TCP socket receive buffer. |
| Values: | Default: 16384 Range: 0 to 64KB if rfc1323=0,
Range: 0 to 4GB if rfc1323=1. Must be less than or equal to sb_max. Should be equal to tcp_sendspace and uniform on all frequently accessed AIX systems. |
| Display: | no -a or no -o tcp_recvspace |
| Change: | no -o tcp_recvspace=newvalue
Change takes effect immediately for new connections. Change is effective until the next system boot. |
| Diagnosis: | Poor throughput. |
| Tuning: | Increase size, preferably to multiple of 4096. |
| Refer to: | Socket Layer. |
| Purpose: | Specify the maximum number of entries on the IP input queue. |
| Values: | Default: 50 Range: N/A |
| Display: | no -a or no -o ipqmaxlen |
| Change: | no -o ipqmaxlen=newvalue
Change takes effect immediately. Change is effective until the next system boot. |
| Diagnosis: | Use crash to access IP input queue overflow counter. |
| Tuning: | Increase size. |
| Refer to: | IP Protocol Performance Tuning Recommendations. |
| Purpose: | Specifies the maximum number of send buffers that can be queued up for the device. |
| Values: | Default: 30 Range: 20 to 150 |
| Display: | lsattr -E -l tok0 -a xmt_que_size |
| Change: | ifconfig tr0 detach
chdev -I tok0 -a xmt_que_size=newvalue ifconfig tr0 hostname up Change is effective across system boots. |
| Diagnosis: | netstat -i
Oerr > 0 |
| Tuning: | Increase size. Should be set to 150 as a matter of course on network-oriented systems, especially servers. |
| Refer to: | LAN Adapters and Device Drivers. |
| Purpose: | (Tunable only in AIX Version 3.) Specifies the maximum number of receive buffers that can be queued up for the interface. |
| Values: | Default: 30 Range: 20 to 150 |
| Display: | lsattr -E -l tokn -a rec_que_size |
| Change: | ifconfig tr0 detach
chdev -I tokn -a rec_que_size=newvalue ifconfig tr0 hostname up Change is effective across system boots. |
| Diagnosis: | None. |
| Tuning: | Increase size. Should be set to 150 as a matter of course on network-oriented systems, especially servers. |
| Refer to: | LAN Adapters and Device Drivers. |
| Purpose: | Limits the size of packets that are transmitted on the network. |
| Values: | trn (4Mb): Default: 1492, Range: 60 to 3900
trn (16Mb): Default: 1492, Range: 60 to 17960 enn: Default: 1500, Range: 60 to 1500 fin: Default: 4352, Range: 60 to 4352 hin: Default: 65536, Range: 60 to 65536 son: Default: 61428, Range: 60 to 61428 lon: Default: 1500 (AIX Version 3.2.5), 16896 (AIX Version 4), Range: 60 to 65536 |
| Display: | lsattr -E -l trn |
| Change: | chdev -l trn -a mtu=NewValue
Cannot be changed while the interface is in use. Because all systems on a LAN must have the same MTU, they must all change simultaneously. Change is effective across boots. |
| Diagnosis: | Packet fragmentation stats |
| Tuning: | Increase MTU size for the Token-Ring interfaces:
trn (4Mb): 4056 trn (16Mb): 8500 For the loopback interface lon in Version 3.2.5, increase to 16896 For other interfaces, the default should be kept. |
| Refer to: | LAN Adapters and Device Drivers. |
The crash command, ifconfig command, lsattr command, netstat command, no command.
The setsockopt subroutine.