HP-UX TCP/IP Performance White Paper, March 2008

A setsockopt() call with a SO_SNDBUF option that exceeds the

corresponding kernel parameter value will fail and return the

errno value EINVAL.

A t_optmgmt() call with an XTI_SNDBUF option that exceeds the

corresponding kernel parameter value will fail and return the

t_errno value TBADOPT.

[1024-2147483647] Default: 2147483647 bytes

This tunable can be used to limit the maximum value for tcp_xmit_hiwater_* and for the value passed-

in via setsockopt() for SO_SNDBUF (similarly XTI_SNDBUF for t_optmgt). In so doing, the

administrator can make sure that no one application can monopolize the memory of the system by asking

for a very large socket buffer and then filling it.

This tunable can also be seen as a way to limit the bandwidth consumed by a TCP application based on

the TCP throughput limit of window-size / round-trip-time.

tcp_xmit_lowater_def:

The amount of unsent data that relieves write-side flow control.

[2048,-] Default: 8192 bytes

tcp_xmit_lowater_lfp:

The amount of unsent data that relieves write-side flow control

for fast links.[2048,-] Default: 16384 bytes

tcp_xmit_lowater_lnp:

The amount of unsent data that relieves write-side flow control

for slow links.[4096,-] Default: 2048 bytes

UDP Tunables

udp_def_ttl:

Default Time-to-Live inserted into IP header. [1,255]

Default: 64

This behaves just as tcp_ip_ttl, only for the IPv4 datagrams containing UDP datagrams.

udp_def_hop_limit:

Default Hop-Limit inserted into IPv6 header. [1,255]

Default: 64

This behaves just as tcp_ip6_hop_limit, only for the IPv6 datagrams containing UDP datagrams.