HP Auto Port Aggregation Administrator's Guide for HP-UX 11i v3 September 2008

Each load distribution algorithm guarantees that it will not introduce any severe ordering
problems within a specific data flow. This is required to ensure that the performance is not
degraded significantly as a result of turning on one of the algorithms.
Also, all packets for a specific data flow always flow out through the same physical port until
the data flow is aged out of the distribution table. This means that in order to generate
simultaneous load on each of the physical ports in a link aggregate, start multiple data flows
over the link aggregate.
Failover Group
HP APA enables you to combine 2 to 32 physical link ports into one failover group. A failover
group is a link aggregate in LAN_MONITOR mode, but with the following differences:
• One port is the active link, and the others are standby links. Network traffic is sent and
received on the active port.
• LAN Monitor periodically exchanges APA packets between the links making up the failover
group. This enables better detection of non-operational links in the failover group.
• If the active port or its link partner fails, LAN Monitor automatically migrates the traffic to
one of the standby ports in the failover group. When a port with a higher priority than the
current active port recovers, the network traffic is migrated back to the previous active port.
Sometimes, it is desirable to have the network traffic remain on the current active port after
the failure and recovery of the previous active port. To achieve this, set the HP APA port
priorities the same for all ports in the failover group.
• You can use 100BT, Gigabit, or 10 Gigabit Ethernet (10GbE) devices in the failover group.
However, all the devices in the failover group must be of one type: 100BT, Gigabit, or 10GbE.
• The failover group can have one or more IP addresses assigned to it.
• The physical ports in the failover group do not share a common MAC address.
• You can include link aggregates in a failover group. This enables increased bandwidth and
load balancing in a failover group.
Proactive Failover
By default, the port in a failover group with the highest priority is the active port. This is called
priority-based failover. However, HP APA also allows you to configure failover groups with
proactive failover.
With proactive failover, the port that is the most efficient at carrying traffic is the active port.
Efficiency is determined by assigning a cost to each port in a failover group. This cost is divided
by the port's current link speed to yield a normalized port cost; link speed is the number of links
in a link aggregate multiplied by the speed of a member link, or in the case of a single link, only
the link speed. The lower the normalized port cost, the higher the link's efficiency. If two links
have the same normalized cost, the one with the higher priority is preferred.
For each failover group, if you assign a cost value to one link, you must assign a cost value to all
other links in the group. If you do not specify a cost value for any of the failover group's links,
the failover group uses the default failover behavior based on priority.
During certain LAN Monitor events (for example, link failure and link recovery), the normalized
port cost might change on the active or standby links. When these events occur, the normalized
port cost of the active link and the standby links are compared. If a standby link has a lower
normalized port cost than the active link, the standby link becomes the active link even if the
current active link is UP.
TCP Segmentation Offload
HP APA supports TCP Segmentation Offload (TSO), also known as Large Send, on link aggregates
and failover groups if all the Ethernet cards are capable of it. TSO is a mechanism by which the
host stack offloads certain portions of outbound TCP packet processing to the Network Interface
Conceptual Overview 15