HP-UX 11i September 2001 Release Notes

Internet and Networking Services
Network Transport (new at 11i original release)
Chapter 10
159
ip_check_subnet_addr shows whether or not that RFC1122 or RFC1878 enforces the
network subnet mask. If it is a 0 (zero), then the RFC1122 behavior is seen. If it is a 1
(one), then RFC1812 is seen. The default is now RFC1812 behavior. See ifconfig for
more information.
This new behavior makes available up to twice as many IP addresses than a similarly
configured RFC1122 machine. This new feature is an enhancement.
2) Selective acknowledgement for TCP supported tcp_sack_enable enables selective
acknowledgement. This enhancement could improve performance in networks with large
transmission windows by allowing TCP recipients to indicate lost segments within large
transmission blocks. The TCP sender can then retransmit only the lost segments.
Supported parameter values are:
2 Local system enables SACK if remote system first sends SACK
(Default).
1 Local system requests the SACK option during a connect() request.
0 Local system never uses SACK.
3) Send and receive buffers now limited to hiwater_max: tcp_hiwater_max and
udp_recv_hiwater_max (default 2GB) set the maximum receive buffer size that
setsockopt or t_optmgmt can set for a socket. tcp_xmit_hiwater_max sets the
maximum send buffer size setsockopt or t_optmgmt can set for a TCP socket. These
systemwide parameters prevent processes from keeping large amounts of data in send or
receive buffers and consuming system resources.
tcp_fin_wait_2 is used to set how long a connection will be in FIN_WAIT_2. Use this
cautiously. If the remote TCP entity is slow, but would terminate normally (is not hung
nor will it terminate abnormally), TCP may close the connection prematurely. A possible
side effect is that data in the remote connections receive buffer may be flushed. If this
happens unexpectedly, then the data could become corrupted.
The above description is an enhancement.
ip_udp_status has a new field. It now will report how many times a given UDP socket
has overflowed. This only works on sockets currently open. This is a very handy
troubleshooting tool used when netstat -p udp shows socket overflows. This feature is
an enhancement.
4) TimeStamps option supported: tcp_ts_enable allows RFC 1323 TimeStamp
extensions to TCP Headers. The TimeStamps are used for two purposes:
1. RTTM (Round TripTime Measurement): Interval between time TCP sends a segment
and the time return acknowledgement arrives.
2. PAWS (Protect Against Wrapped Sequences) on high-speed networks.
Supported parameter values are:
2 Use Timestamps option if initiated by the remote system
1 Always try to initiate the use of Timestamps option
0 Never use Timestamps option
5) Socket structure caching can increase performance: tcp_conn_strategy enables
socket caching. It sets how many cached socket structures the system keeps. The default
value of 0 (zero) disables the feature. A value between 1 and 512 sets a minimum of 512.
Any number above 512 sets tcp_conn_strategy to that value. Enabling socket structure