Ethernet Support Guide for HP-UX 11i v3

Example 19 Displaying the current TSO setting
Use the nwmgr command in the following format to display the TSO capability of the link. An
output example follows.
# nwmgr -g -A vmtu -c lanppa
Driver/Hardware supports TCP Segmentation Offload. Current VMTU = 32160
Example 20 Setting the TSO capability for a link
TSO is enabled or disabled for a link by defining a VMTU parameter in the device configuration
file or by using the nwmgr command to modify the VMTU parameter.
The configuration file parameter is in the format HP_driver_VMTU, such as HP_ICXGBE_VMTU.
The nwmgr TSO parameter is vmtu. To enable TSO, set the VMTU parameter value to 32160. To
disable TSO, set the parameter to 0.
NOTE: Transmit CKO must be enabled (for information about setting CKO, see Section 3.9
(page 32)).
For the iether and igelan drivers, TSO is disabled by default. For the 10Gigabit drivers, TSO
is enabled by default.
To set the parameter value to persist across reboots (recommended), edit the driver's configuration
file to specify the HP_driver_VMTU parameter value. For example, to enable TSO for all ports
on an iocxgbe driver device, specify the parameter as follows:
HP_IOCXGBE_VMTU=32160
To use the nwmgr command to enable TSO immediately and permanently, use the --sa option
as in the following example:
#nwmgr --sa -A vmtu=new_vmtu_value -c lanppa
Changes to the Output of Current Commands
If you are using NetTL or tcpdump to trace outbound packets, you may see these differences:
tracing outbound packets in the host will display large packets being transmitted on the link, while
tracing the packets on the wire or at the receiving end will display only packets that are less than
or equal to the link MTU size.
TSO Interaction with Other Software
TSO is supported on virtual LANs (VLANs). It is supported for all MTU values (that is, TSO is
supported with Jumbo frames) and speed settings on the link. Both Ethernet and SNAP encapsulations
are supported.
TSO is supported on link aggregations starting with the September 2004 version of the HP Auto
Port Aggregation (APA) product. For further details, see the latest release notes for the HP APA
product at the following location:
http://www.hp.com/go/hpux-APA-docs
3.11 Displaying and setting the TCP segment reassembly parameter
TCP segment reassembly (also known as TCP packet reassembly and Large Receive Offload)
combines TCP segments of data and passes the large, combined packet to the upper layers of the
network stack in the receive path. This can lower CPU utilization. This feature is supported by
10GbE drivers only.
3.11 Displaying and setting the TCP segment reassembly parameter 35