Technical data

Tuning Techniques
2.1 Subsystem Attributes
2.1.6.9 Modifying the Range of Outgoing Connection Ports
When a TCP or UDP application creates an outgoing connection, the kernel
dynamically allocates a nonreserved port number for each connection. The
kernel selects the port number from a range of values between the value of
the inet subsystem attribute ipport_userreserved_min and the value of the
ipport_userreserved attribute. Using the default values for these attributes, the
range of outgoing ports starts at 49152 and stops at 65535.
Performance Benefits and Tradeoffs
Modifying the range of outgoing connections provides TCP and UDP applications
with a specific range of ports.
You can modify the
ipport_userreserved_min and ipport_userreserved
attributes without rebooting the system.
When to Tune
If your system requires outgoing ports from a particular range, you can
modify the values of the
ipport_userreserved_min and ipport_userreserved
attributes.
Recommended Values
The default value of the
ipport_userreserved_min attribute is 49152. The
default value of the ipport_userreserved is 65535. The maximum value of each
attribute is 65535.
Do not reduce the ipport_userreserved attribute to a value that is less than
65535, and do not reduce the ipport_userreserved_min attribute to a value that
is less than 49152.
2.1.6.10 Disabling Use of the PMTU Protocol
Packets transmitted between servers are fragmented into units of a specific size
in order to ease transmission of the data over routers and small-packet networks,
such as Ethernet networks. When the
inet subsystem attribute pmtu_enabled
is enabled (set to 1, which is the default behavior), the system determines the
largest common path maximum transmission unit (PMTU) value between servers
and uses it as the unit size. The system also creates a routing table entry for
each client network that attempts to connect to the server.
Performance Benefits and Tradeoffs
If a server handles traffic among many remote clients, disabling the use of a
PMTU can decrease the size of the kernel routing table, which improves server
efficiency. However, on a server that handles local traffic and some remote traffic,
disabling the use of a PMTU can degrade bandwidth.
When to Tune
If an Internet server has poor performance and the routing table increases
to more than 1000 entries, you should disable the use of PMTU. This is also
recommended if you have a server that handles traffic among many remote
clients.
Recommended Values
To disable the use of PMTU protocol, set the value of the
pmtu_enabled attribute
to 0.
2–14 Tuning Techniques