Split Trunking Support with HP Auto Port Aggregation

Overview
The IEEE 802.3ad standard defines link aggregation on a single switch, but different switch vendors
have implemented extensions that allow a single link aggregation to span across two or more of their
interconnected network switches. The term split trunking as used in this document refers to such cross-
switch link aggregation technologies. Two particular split trunking implementations referred to in this
document are Nortel SMLT and Cisco stackwise cross-stack EtherChannel.
This document describes how HP Auto Port Aggregation (APA) can support the Cisco cross-stack
EtherChannel or Nortel Split Multi-Link Trunking (SMLT) technologies. This document is relevant for
users of APA link aggregations only. It has no relevance for users of APA LAN Monitor failover
groups.
Definition of Split Trunking
Split trunking is a link aggregation whose link partners reside on two or more switches. Traffic must
be able to be moved from one switch to another in case one switch fails.
Benefits of Split Trunks
Split trunks improve the availability of a network configuration using link aggregations by eliminating
the switch as a single point of failure (SPOF). If a switch fails, traffic on the link aggregation continues
on the remaining switches. Figures 1 and 2 show this concept. In Figure 1, the physical links of the
link aggregation lan900 is connected to one switch. If the switch fails, the link aggregate becomes
unusable.
2