Foundry NetIron M2404C and M2404F Metro Access Switches
Configuring Interfaces (Rev. 03)
Link Aggregation Groups (LAG)
© 2008 Foundry Networks, Inc.
Page 26 of 57
Overview
Static Link Aggregation Groups (LAGs)
Static LAGs provide the ability to treat multiple device ports as one device port. These port groups
act as a single logical port for high-bandwidth connections between two network devices. A static
LAG balances the traffic load across the links in the channel. If a physical link within the static
LAG fails, traffic previously carried over the failed link is moved to the remaining links. Most
protocols operate over either single ports or aggregated device ports and do not recognize the
physical ports within the port group.
A static LAG consists of individual Fast Ethernet or Gigabit Ethernet links bundled into a single
logical link as shown in
Figure 2.
LAGs Benefits
Static LAGs provide the following benefits:
•
Increased bandwidth
The capacity of multiple interfaces is combined into one logical link. Besides increasing
bandwidth, link aggregation also provides intermediate data rate levels between the standard
data rates of 10 Mbps, 100 Mbps, and 1000 Mbps, as well as rates beyond 1000 Mbps if
required.
•
Increased availability
If a link within a LAG fails or is replaced, the traffic is not disrupted and communication is
maintained (even though the available capacity is reduced).
•
Load sharing
Traffic is distributed across multiple links, minimizing the probability that a single link be
overwhelmed.
•
Use of existing hardware
Software replaces the need to upgrade the hardware to higher bandwidth capacity.
The Link Aggregation Control Protocol (LACP)
LACP, specified in the IEEE standard 802.3ad, provides a standardized means for dynamically
exchanging information between two devices in order to configure and maintain link aggregation
groups automatically. LACP can automatically detect the presence of other aggregation-capable
network devices in the system. It enables the user to determine which links can be aggregated in the
system. For each aggregated link, the devices exchange LACP frames for synchronizing the
databases of the connected LACP enabled ports. In order to group the ports to a Link Aggregation
Group, the LACP analyzes the database periodically to detect LACP enabled ports.
LACP Modes
The LACP interface supports two modes of operation, as follows: