Alteon Application Switch Operating System Application Guide
Port Trunking
Document ID: RDWR-ALOS-V2900_AG1302
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Link Aggregation Control Protocol Trunking
The Link Aggregation Control Protocol (LACP) is an IEEE 802.3ad standard for grouping several
physical ports into one logical port (known as a trunk group or a link aggregation group) with any
device that supports the standard. If a link in a LACP trunk group fails, traffic is reassigned
dynamically to any of the remaining links of the LACP trunk group. Link aggregation is a method of
grouping physical link segments of the same media type and speed in full duplex, and treating them
as if they were part of a single, logical link segment. Refer to IEEE 802.3ad-2002 for a full
description of the standard.
When using LACP, any trunk groups you may have already configured according to the manual
procedure described in
are "static trunks." Any trunk groups using
LACP are "dynamic trunks." With LACP, the maximum number of trunk groups has increased to 40.
Static trunks continue to be limited to trunk IDs 1 through 12, and LACP trunks use IDs 13 through
40.
The Alteon implementation of LACP lets you group a maximum of eight physical ports into one
logical port (LACP trunk group). Standby ports in LACP are created only when there are more than
eight LACP ports configured in a trunk. Alteon assigns any non-trunked LACP-configured ports as
standby ports for the LACP trunk. If any of the eight primary LACP ports fails, Alteon dynamically
replaces it with the standby port.
Alteon can form trunk groups with any device which supports the IEEE 802.3ad standard.
Each LACP port has a parameter called admin key. An LACP trunk group is formed with the ports
with the same admin key. The value of admin key can be any integer between 1 and 65535.
Example
Actor Versus Partner LACP Configuration
In this example, actor device ports 1 through 4 can aggregate to form an LACP trunk group with the
partner device ports 1 through 4. Note that the port admin key value has local significance only. The
admin key value for the partner device ports can be any integer value but it should be same for all
ports 1 through 4. In this example, it is 50.
LACP Modes
Each port can have one of the following LACP modes:
•
off (default)—The user can configure this port into a regular static trunk group.
•
active—The port is capable of forming an LACP trunk. This port sends LACP data unit (LACPDU)
packets to partner system ports.
•
passive—The port is capable of forming an LACP trunk. This port only responds to the LACPDU
packets sent from an LACP active port.
Each active LACP port transmits LACPDUs, while each passive LACP port listens for LACPDUs. During
LACP negotiation, the admin key value is exchanged. The LACP trunk group is enabled as long as the
information matches at both ends of the link. If the admin key value changes for a port at either end
of the link, that port's association with the LACP trunk group is lost.
Table 10: Actor Versus Partner LACP Configuration
Actor Device
Partner Device 1
Port 1 (admin key = 100)
Port 1 (admin key = 50)
Port 2 (admin key = 100)
Port 2 (admin key = 50)
Port 3 (admin key = 100)
Port 3 (admin key = 50)
Port 4 (admin key = 100)
Port 4 (admin key = 50)
