Netis ST3326(ST-3302) [35/118] Chapter7 redundancy

Chapter7: Redundancy

Understanding EtherChannels

EtherChannel provides fault-tolerant high-speed links between switches, routers, and servers.

You can use it to increase the bandwidth among the wiring closets and the data center, and you

can deploy it anywhere in the network where bottlenecks are likely to occur. EtherChannel

provides automatic recovery for the loss of a link by redistributing the load across the remaining

links. If a link fails, EtherChannel redirects traffic from the failed link to the remaining links in the

channel without intervention.

Each EtherChannel can consist of up to eight compatibly configured Ethernet interfaces. All

interfaces in each EtherChannel must be the same speed, and all must be configured as Layer 2

interfaces.

Introduction to Link Aggregation

Link aggregation can aggregate multiple Ethernet ports together to form a logical aggregation

group. To upper layer entities, all the physical links in an aggregation group are a single logical

link.

Link aggregation is designed to increase bandwidth by implementing outgoing/incoming load

sharing among the member ports in an aggregation group. Link aggregation group also allows for

port redundancy, which improves connection reliability.

Introduction to LACP

Link aggregation control protocol (LACP) is designed to implement dynamic link aggregation and

deaggregation. This protocol is based on IEEE802.3ad and uses link aggregation control protocol

data units (LACPDUs) to interact with its peer.

With LACP enabled on a port, LACP notifies the following information of the port to its peer by

sending LACPDUs: priority and MAC address of this system, priority, number and operation key

of the port.

Upon receiving the information, the peer compares the information with the information of

other ports on the peer device to determine the ports that can be aggregated. In this way, the

two parties can reach an agreement in adding/removing the port to/from a dynamic aggregation

group.

Operation key is generated by the system. It is determined by port settings such as port speed,

duplex mode, and basic configurations.

 Selected ports in a manual aggregation group or a static aggregation group have the same

operation key.

 Member ports in a dynamic aggregation group have the same operation key.

Exchanging LACP Packets

Both the active and passive LACP modes allow interfaces to negotiate with partner interfaces to

determine if they can form an EtherChannel based on criteria such as interface speed and, for