Allied Telesis AlliedWare Plus Operating System Version 5.4.4C (x310-26FT,x310-26FP,x310-50FT,x310-50FP) User Manual
Page 560
Link Aggregation Introduction and Configuration
Software Reference for x310 Series Switches
20.4
AlliedWare Plus
TM
Operating System - Version 5.4.4C
C613-50046-01 REV A
LACP operates where systems are connected over multiple communications links. Once
LACP has been initially configured and enabled, it automatically aggregates the ports that
have been assigned to a channel group, if possible. LACP continues to monitor these
groups and dynamically adds or removes links to them as network changes occur.
LACP achieves this by determining:
■
which ports are under LACP control (
channel-group command on page 21.4
■
whether each port is in LACP active or LACP passive mode (
■
which system has the highest LACP priority (
lacp system-priority command on page
■
the LACP priority of ports (
lacp port-priority command on page 21.7
■
whether the LACP timeout is short or long (
lacp timeout command on page 21.8
Channel group
identification
In order to identify particular channel groups, each group is assigned a link aggregation
identifier called a lag ID. The lag ID comprises the following components for both the local
system (called the Actor) followed by their equivalent components for the remote system
(called the Partner):
■
system identifier - the MAC address of the system
■
port key - An identifier - created by the LACP software
■
port priority - set by the
lacp port-priority command on page 21.7
■
port number - determined by the device connection
The lag ID can be displayed for each aggregated link by entering the
.
Note
AlliedWare Plus
TM
supports IEEE 802.3ad link aggregation and uses the Link
Aggregation Control Protocol (LACP). LACP does not interoperate with devices
that use Port Aggregation Protocol (PAgP).
Note
Link aggregation does not necessarily achieve exact load balancing across the
links. The load sharing algorithm is designed to ensure that any given data flow
always goes down the same link. It also aims to spread data flows across the
links as evenly as possible.
Link aggregation hashes the source and destination MAC address, IP address
and UDP/TCP ports to select a link on which to send a packet. So packet flow
between a pair of hosts always takes the same link inside the Link Aggregation
Group (LAG). The net effect is that the bandwidth for a given packet stream is
restricted to the speed of one link in the LAG.
For example, for a 2 Gbps LAG that is a combination of two 1 Gbps ports, one
flow of traffic can only ever reach a maximum throughput of 1 Gbps. However,
the hashing algorithm should spread the flows across the links so that when
many flows are operating, the full 2 Gbps can be utilized.
For information about load balancing see the
command