HP Auto Port Aggregation Administrator's Guide for HP-UX 11i v3 December 2007

When a physical port is removed from a link aggregate, the port's MAC address is reset to
its own MAC address.
• HP APA link aggregates can migrate the network traffic from a failed physical link in the
aggregate to the remaining operational links in the aggregate.
• HP APA distributes the outbound network traffic across the physical links in the link
aggregation using a load balancing algorithm.
Effective APA load balancing requires many simultaneous, active client connections. The
connections are distributed across the physical links. One client connection will have its
traffic sent on one physical link. The connection is defined by the load-balancing algorithm.
See “Load Balancing” (page 18) for more information.
• Each link aggregate can have one or more IP addresses assigned to it in the
/etc/rc.config.d/netconf file.
• The link partner (the switch, router, or server) ports connected to the server ports must be
configured for link aggregation (trunking). In addition, the mode on the link partner and
the server must be the same. For example, if ports 1, 2, 3, and 4 are connected to a link partner
switch's ports C1, C2, C3, and C4, respectively, and the server side is trunked using
LACP_AUTO mode, the partner switch must be configured to trunk ports C1, C2, C3, and
C4 using LACP_AUTO mode.
NOTE: MANUAL mode link aggregates using HOT_STANDBY load balancing can be
connected to different switches. In addition, do not enable trunking on the corresponding
switch ports.
• The link partner (the switch, router, or server) connected to the link aggregation can inhibit
the usefulness of HP APA in some environments. See “HP APA Configuration Examples”
(page 27) for more information.
• All the devices in the link aggregation must be the same type and must be configured for
the same speed, duplex, and MTU. See “Supported LAN Cards” (page 23) for the devices
HP APA supports.
Load Balancing
HP APA provides load balancing on outbound data transfers using a load distribution algorithm
that you select when you configure a link aggregate. The load distribution algorithms are based
on destination MAC address, IP address, or TCP/UDP port number. Inbound load balancing is
strictly determined by the link partner (switch, router, or remote server) and has no affect on the
outbound algorithms.
Although you can use each of these load distribution algorithms in all supported configurations,
they may not all provide the same load on each of the physical ports in the link aggregate.
Therefore, HP prefers you use the algorithm that is recommended for each supported
configuration. See “Preparing for Configuration” (page 35) for more information.
The load balancing algorithm consists of the following steps:
1. Data Flow Lookup — The load distribution algorithm determines an index into a hash table
that includes the physical port through which the outbound data flow is forwarded.
2. Data Flow Physical Port Assignment — If the hash index for the data flow has not been
assigned a physical port (the entry is empty), a physical port in the link aggregate is assigned
to that specific hash index. The physical port is selected on a Round Robin basis.
3. Aging Data Flows — Over time, each data flow is checked to determine if it is still active.
If the data flow has not been active in the last 30 seconds, its specific hash index is cleared
(aged out). If the data flow restarts after being cleared from the hash table, it is reassigned
a new physical port on a Round Robin basis. For information on clearing a data flow and
initiating the load balancing process, see “Resetting a Data Flow” (page 60).
18 Introduction