Ethernet link aggregation, or simply link aggregation, combines multiple physical Ethernet ports into one logical link called an "aggregate link." Link aggregation delivers the following benefits:

· Increases bandwidth beyond the limits of any single link. In an aggregate link, traffic is distributed across the member ports.

· Improves link reliability. The member ports dynamically back up one another. When a member port fails, its traffic is automatically switched to other member ports.

As shown in Figure 1, the AP and the switch are connected by two physical Ethernet links. These physical Ethernet links are combined into an aggregate link called link Aggregation 1. The bandwidth of this aggregate link can reach up to the total bandwidth of the two physical Ethernet links. At the same time, the two Ethernet links back up one another.

Figure 1 Ethernet link aggregation

Basic concepts

This section describes some basic link aggregation concepts.

Aggregation group, member port, and aggregate interface

Link aggregation is implemented by combining Ethernet interfaces into a link aggregation group. Each link aggregation group has one logical aggregate interface.

The rate of an aggregate interface equals the total rate of its member ports in Selected state. Its duplex mode is the same as that of the Selected member ports. For more information about the states of member ports in an aggregation group, see "Aggregation states of member ports in an aggregation group."

When you create an aggregate interface, the device automatically creates an aggregation group of the same type and number as the aggregate interface. For example, when you create interface Bridge-Aggregation 1, Layer 2 aggregation group 1 is automatically created.

You can assign Layer 2 Ethernet interfaces only to a Layer 2 aggregation group.

NOTE:

The device supports only Layer 2 aggregation groups and aggregate interfaces.

Aggregation states of member ports in an aggregation group

A member port in an aggregation group can be in either of the following aggregation states:

· Selected—A Selected port can forward user traffic.

· Unselected—An Unselected port cannot forward user traffic.

When a Selected port fails, an Unselected port may become a Selected port and forward user traffic.

Operational key

When aggregating ports, the system automatically assigns each port an operational key based on port information such as port rate and duplex mode. Any change to this information triggers a recalculation of the operational key.

In an aggregation group, all selected member ports are assigned the same operational key.

Configuration classes

Every configuration setting on a port might affect its aggregation state. Port configurations fall into the following classes:

· Port attribute configurations—Include port rate, duplex mode, and link status (up or down). These are the most basic port configurations.

· Class-two configurations—A member port can be placed in Selected state only if it has the same class-two configurations as the aggregate interface. Class-two configurations made on an aggregate interface are automatically synchronized to all its member ports. These configurations are retained on the member ports even after the aggregate interface is removed.

Table 1 Class-two configurations

Feature	Considerations
VLAN	Permitted VLAN IDs, PVID, link type (trunk, hybrid, or access), VLAN tagging mode.
MAC address learning	MAC address learning capability, MAC address learning limit, forwarding of frames with unknown destination MAC addresses after the MAC address learning limit is reached.

NOTE:

Any class-two configuration change might affect the aggregation state of link aggregation member ports and ongoing traffic. To be sure that you are aware of the risk, the system displays a warning message every time you attempt to change a class-two configuration setting on a member port.

· Class-one configurations—Include settings that do not affect the aggregation state of the member port even if they are different from those on the aggregate interface. The spanning tree settings are examples of class-one configurations. The class-one configuration of a member port is effective only when the member port leaves the aggregation group.

Reference port

When setting the aggregation state of the ports in an aggregation group, the system automatically chooses a member port as the reference port. A Selected port must have the same port attributes and class-two configurations as the reference port. For information about how a reference port is chosen in a static link aggregation group, see "Choosing a reference port" in the section "Aggregating links in static mode."

Aggregating links in static mode

You must manually maintain the aggregation state of the member ports in a static aggregation group.

Choosing a reference port

The system chooses a reference port from the UP member ports that have the same class-two configurations as the aggregate interface.

The candidate ports are sorted by aggregation priority, duplex, and speed in the following order:

· Lowest aggregation priority value

· Full duplex/high speed

· Full duplex/low speed

· Half duplex/high speed

· Half duplex/low speed

The one at the top is chosen as the reference port. If two ports have the same aggregation priority, duplex mode, and speed, the one with the lower port number is chosen.

Setting the aggregation state of each member port

After choosing the reference port, the static aggregation group sets the aggregation state of each member port, as shown in Figure 2. After the static aggregation group has reached the limit on Selected ports, any port assigned to the group is placed in Unselected state to avoid traffic interruption on the current Selected ports.

Figure 2 Setting the aggregation state of a member port in a static aggregation group

Load sharing criteria for link aggregation groups

In a link aggregation group, traffic can be load shared across the Selected member ports based on a set of criteria, depending on your configuration.

You can choose one or any combination of the following criteria for load sharing:

· Source or destination MAC addresses.

· Source or destination IP addresses.

Feature and hardware compatibility

Hardware series	Model	Ethernet link aggregation compatibility
WA4300 series	WA4320-ACN	No
	WA4320-ACN-PI	No
	WA4320H-ACN	No
	WA4320i-ACN	Yes
WA4600 series	WA4620i-ACN/WA4620E-ACN	Yes

Configuration restrictions and guidelines

When you configure a link aggregation group, follow these restrictions and guidelines:

· To ensure stable aggregation state and service continuity, do not change port attributes or class-two configurations on any member port. If you must, make sure you understand its impact on the live network. Any port attribute or class-two configuration change might affect the aggregation state of link aggregation member ports and ongoing traffic.

· Avoid assigning ports to a static aggregation group that has reached the limit on Selected ports. These ports will be placed in Unselected state to avoid traffic interruption on the current Selected ports. However, a device reboot can cause the aggregation state of member ports to change.

Ethernet link aggregation configuration task list

Task	Remarks
Configuring a Layer 2 static aggregation group	Required.
Configuring an aggregate interface: · Configuring the description of an aggregate interface · Enabling link state traps for an aggregate interface · Shutting down an aggregate interface · Restoring the default settings for an aggregate interface	Optional.
Configuring load sharing criteria for link aggregation groups: · Configuring the global link-aggregation load sharing criteria · Configuring the group-specific load sharing criteria	Optional.

Configuring a Layer 2 static aggregation group

Configuration restrictions and guidelines

When you configure a Layer 2 aggregation group, follow these restrictions and guidelines:

· You cannot assign a port to a Layer 2 aggregation group if any of the features listed in Table 2 is configured on the port.

Table 2 Features incompatible with Layer 2 aggregation groups

Feature	Reference
MAC authentication	MAC authentication in Security Configuration Guide
Port security	Port security in Security Configuration Guide
802.1X	802.1X in Security Configuration Guide

· To guarantee a successful static aggregation, make sure the ports at both ends of each link are in the same aggregation state.

· Deleting an aggregate interface also deletes its aggregation group. At the same time, all member ports leave the aggregation group.

Configuration procedure

To configure a Layer 2 static aggregation group:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Create a Layer 2 aggregate interface and enter Layer 2 aggregate interface view.	interface bridge-aggregation interface-number	When you create a Layer 2 aggregate interface, the system automatically creates a Layer 2 static aggregation group numbered the same. The value for the interface-number argument can only be 1.
3. Exit to system view.	quit	N/A
4. Assign a Layer 2 Ethernet interface to the aggregation group.	a. interface interface-type interface-number b. port link-aggregation group number	Repeat this step to assign more Layer 2 Ethernet interfaces to the aggregation group.
5. Assign the port an aggregation priority.	link-aggregation port-priority port-priority	Optional. By default, the aggregation priority of a port is 32768. When the number of ports eligible for Selected ports exceeds the maximum number of Selected ports allowed in a static aggregation group, changing the aggregation priority of a port may affect the aggregation state of the ports in the static aggregation group.

Configuring an aggregate interface

Most of the configurations that can be performed on Layer 2 Ethernet interfaces can also be performed on Layer 2 aggregate interfaces.

Configuring the description of an aggregate interface

You can configure the description of an aggregate interface for administration purposes such as describing the purpose of the interface.

To configure the description of an aggregate interface:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter Layer 2 aggregate interface view.	interface bridge-aggregation interface-number	N/A
3. Configure the description of the aggregate interface.	description text	Optional. By default, the description of an interface is in the format of interface-name Interface, such as Bridge-Aggregation1 Interface.

Enabling link state traps for an aggregate interface

You can configure an aggregate interface to generate linkUp trap messages when its link goes up and linkDown trap messages when its link goes down. For more information, see Network Management and Monitoring Configuration Guide.

To enable link state traps on an aggregate interface:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enable the trap function globally.	snmp-agent trap enable [ standard [ linkdown \| linkup ] * ]	Optional. By default, link state trapping is enabled globally.
3. Enter Layer 2 aggregate interface view.	interface bridge-aggregation interface-number	N/A
4. Enable link state traps for the aggregate interface.	enable snmp trap updown	Optional. Enabled by default.

Shutting down an aggregate interface

Shutting down or bringing up an aggregate interface affects the aggregation state and link state of aggregated member ports in the following ways:

· When an aggregate interface is shut down, all Selected member ports become unselected and their link state becomes down.

· When an aggregate interface is brought up, the aggregation state of member ports is recalculated and their link state becomes up.

To shut down an aggregate interface:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter Layer 2 aggregate interface view.	interface bridge-aggregation interface-number	N/A
3. Shut down the aggregate interface.	shutdown	By default, aggregate interfaces are up.

Restoring the default settings for an aggregate interface

Step	Command
1. Enter system view.	system-view
2. Enter Layer 2 aggregate interface view.	interface bridge-aggregation interface-number
3. Restore the default settings for the aggregate interface.	default

Configuring load sharing criteria for link aggregation groups

You can determine how traffic is load shared in a link aggregation group by configuring load sharing criteria. The criteria can be source or destination MAC addresses, source or destination IP addresses, or any combination.

You can configure global or group-specific load sharing criteria. A link aggregation group preferentially uses the group-specific load sharing criteria. If the group-specific load sharing criteria are not available, the group uses the global load sharing criteria.

Configuring the global link-aggregation load sharing criteria

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Configure the global link-aggregation load sharing criteria.	link-aggregation load-sharing mode { destination-ip \| destination-mac \| source-ip \| source-mac }	By default, the global load sharing criteria are source and destination MAC addresses.

Configuring the group-specific load sharing criteria

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter Layer 2 aggregate interface view.	interface bridge-aggregation interface-number	N/A
3. Configure the load sharing criteria for the aggregation group.	link-aggregation load-sharing mode { destination-ip \| destination-mac \| source-ip \| source-mac }	By default, an aggregation group load shares traffic based on source and destination MAC addresses.

Displaying and maintaining Ethernet link aggregation

Task	Command	Remarks
Display information about aggregate interfaces.	display interface bridge-aggregation [ interface-number ] [ brief [ down ] ] [ \| { begin \| exclude \| include } regular-expression ]	Available in any view.
Display the global or group-specific link-aggregation load sharing criteria.	display link-aggregation load-sharing mode [ interface [ bridge-aggregation interface-number ] ] [ \| { begin \| exclude \| include } regular-expression ]	Available in any view.
Display detailed link aggregation information for link aggregation member ports.	display link-aggregation member-port [ interface-list ] [ \| { begin \| exclude \| include } regular-expression ]	Available in any view.
Display summary information about all aggregation groups.	display link-aggregation summary [ \| { begin \| exclude \| include } regular-expression ]	Available in any view.
Display detailed information about a specific or all aggregation groups.	display link-aggregation verbose [ bridge-aggregation [ interface-number ] ] [ \| { begin \| exclude \| include } regular-expression ]	Available in any view.
Clear statistics for a specific or all aggregate interfaces.	reset counters interface [ bridge-aggregation [ interface-number ] ]	Available in user view.

Layer 2 static aggregation configuration example

In an aggregation group, only ports that have the same port attributes and class-two configurations (see "Configuration classes") as the reference port (see "Reference port") can operate as Selected ports. Make sure all member ports have the same port attributes and class-two configurations as the reference port. The other settings only need to be configured on the aggregate interface, not on the member ports.

Network requirements

As shown in Figure 3, perform the following tasks:

· Configure a Layer 2 static aggregation group on the AP and the switch.

· Enable traffic to be load shared across aggregation group member ports based on the source and destination MAC addresses.

Figure 3 Network diagram

Configuration procedure

1. Configure the AP:

# Create Layer 2 aggregate interface Bridge-Aggregation 1.

[AP] interface bridge-aggregation 1

[AP-Bridge-Aggregation1] quit

# Assign ports GigabitEthernet 1/0/1 and GigabitEthernet 1/0/2 to link aggregation group 1.

[AP] interface GigabitEthernet 1/0/1

[AP-GigabitEthernet1/0/1] port link-aggregation group 1

[AP-GigabitEthernet1/0/1] quit

[AP] interface GigabitEthernet 1/0/2

[AP-GigabitEthernet1/0/2] port link-aggregation group 1

[AP-GigabitEthernet1/0/2] quit

# Configure the global link-aggregation load sharing criteria as source and destination MAC addresses.

[AP] link-aggregation load-sharing mode source-mac destination-mac

2. Configure the switch in the same way the AP is configured. (Details not shown.)

3. Verify the configurations:

# Display summary information about all aggregation groups on the AP.

[AP] display link-aggregation summary

Aggregation Interface Type:

BAGG -- Bridge-Aggregation

Loadsharing Type: Shar -- Loadsharing, NonS -- Non-Loadsharing

AGG Select Unselect Share

Interface Ports Ports Type

--------------------------------------------------------------------------------

BAGG1 2 0 Shar

The output shows that link aggregation group 1 is a load-shared Layer 2 static aggregation group and it contains two Selected ports.

# Display the global link-aggregation load sharing criteria on the AP.

[AP] display link-aggregation load-sharing mode

Link-Aggregation Load-Sharing Mode:

destination-mac address, source-mac address

The output shows that all link aggregation groups created on the AP perform load sharing based on source and destination MAC addresses.

03-Layer 2 Configuration Guide

Aggregation group, member port, and aggregate interface

Operational key

Setting the aggregation state of each member port

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