Transition Networks
S4224 Web User Guide
33558 Rev. C
Page 145 of 669
LACP (Link Aggregation Control Protocol)
This page is used to configure the Aggregation hash mode and the aggregation group from
Configuration
>
Aggregation
>
LACP
. The Link Aggregation Control Protocol (LACP) is an IEEE
802.3ad standard that allows bundling several physical ports together to form a single logical port.
The S4224 supports Link aggregation per IEEE 802.1AX-2008. The Link aggregation supports several
physical links bundled into a single logical link for resiliency and load sharing. The S4224 uses LACP
PDUs to negotiate with peer devices and to exchange information about the links to be bundled
automatically when enabled on the physical port.
The resolved aggregation status and peer information status are available. The load sharing mechanism
uses all the physical links to transfer the traffic, but for a flow only one link can be used to make sure the
packets are sent/received in order. It uses a hash function to determine which port should carry a traffic
flow. The device lets you choose the fields that are needed for generating the hash code needed for
routing a flow through a single physical port belonging to the aggregate group.
LACP takes care of link failures where if one link fails the flows belonging to that link are transferred to
another link based on the hash mechanism which needs to choose from the available links.
The static aggregation option is also supported so the S4224 will work with devices which don’t support
LACP.
LACP works by sending frames (LACPDUs) down all links that have the protocol enabled. If it finds a
device on the other end of the link that also has LACP enabled, it will also independently send frames
along the same links enabling the two units to detect multiple links between themselves and then
combine them into a single logical link. LACP can be configured in one of two modes: active or passive.
In active mode it will always send frames along the configured links. In passive mode however, it acts as
"speak when spoken to", and therefore can be used as a way of controlling accidental loops (as long as
the other device is in active mode).
LACP has advantages over static configuration. For instance, with failover when a link fails and there is
another device such as a Media Converter between the devices, which means that the peer will not see
the link down. With static link aggregation the peer would continue sending traffic down the link causing it
to be lost. The device can confirm that the configuration at the other end can handle link aggregation.
With Static link aggregation, a cabling or configuration mistake could go undetected and cause
undesirable network behavior.
Guidelines for creating LACP aggregations
:
The LACP module can have a maximum of 3 groups (number of ports / 2), and up to 6 ports can be
in a LAG (Link Aggregation Group) at any time.
LACP must be activated on both the S4224 and its partner device.
The other device must be 802.3ad-compliant.
The ports of an aggregate trunk must be the same medium type (all TP ports or all fiber ports).
Aggregation ports can be consecutive (e.g., ports 1-5) or nonconsecutive (e.g., ports 2, 4, 6).
A port can belong to only one LACP aggregator at a time.
A port cannot be a member of an LACP aggregator and a static aggregation concurrently.
The ports of an aggregate trunk must be untagged members of the same VLAN.
LACP trunking is not supported in half-duplex mode. Twisted-pair ports must be set to Auto-
Negotiation or 1000 Mbps / full-duplex mode.
1000Base-X fiber optic ports must be set to full-duplex mode.
Only ports that are members of an aggregator will transmit LACPDU packets.
A member port of an aggregator functions as part of an aggregate trunk only if it receives LACPDU
packets from the remote device. If it does not receive LACPDU packets, it functions as a normal
Ethernet port (forwarding network traffic while continuing to transmit LACPDU packets).
