Overview
A link aggregation group (LAG) combines multiple physical links into a single logical interface which is referred to as a bundle interface. These physical links are connected between two devices. The device uses LACP protocol to bundle the member links and create high speed connections. Although a bundle can be created based on static configuration, bandwidth can be increased by adding member links to the bundle. This also allows load sharing among the physical links. Thus, a group of ports combined together is called a link aggregation group, or LAG.
The LAG interface combines the bandwidth of the individual member links. The properties like speed and bandwidth of the individual member links should be the same to make it part of that LAG. The traffic which is directed towards the LAG interface is sent on the individual member links. This traffic is not pinned to a specific member link but rather determined by a specific flow. This hash could be calculated based on various fields in the packet.
Supported Platforms
Not all features are necessarily supported on each hardware platform. Refer to the Platform Guide for the features and the sub-features that are or are not supported by each platform.
LAG Interface Modes
The LAG interface could be formed statically or dynamically. LACP protocol helps to bring up the interface dynamically. The two modes of LAG interface are:
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Static LAG: In this mode, the member links do not initiate or process any of the LACP packets received. The device brings up the LAG interface without LACP negotiation.
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Dynamic LAG: In this mode, the member links process the LACP packets received. Under this mode, there two sub modes:
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active: LACP packets are generated on each of the member links on the transmit side.
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passive: LACP packets are generated on the member link in response to the LACP packet received. That means, at least one side of the LAG should be configured as
activeto bring up the LAG interface.
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Layer2 and Layer 3 Interfaces
LAG interfaces can be used as layer 2 and layer 3 interfaces. A regular layer 2 or layer 3 interface can be created on top of the single LAG interface. These interfaces can be divided based on 802.1q VLAN ID’s. Multiple layer 3 interfaces can be created and each of them can be associated with different instances.
LACP (Link Aggregation Control Protocol)
LACP is part of an IEEE specification (802.3ad) that allows several physical ports to be grouped to form a single logical interface. LACP allows a switch to negotiate an LAG by sending LACP packets on its member links. It negotiates the various configuration parameters to bring up the individual member links.
Supported Number of LAG Interfaces on Platforms
The following tables provide maximum number of LAG interfaces and members per LAG supported on each hardware platform.
Access-Leaf Platforms
| Platform | Max. Number of LAG Interfaces Supported | Number of LAG Members Supported |
|---|---|---|
UfiSpace S9600-72XC |
72 |
10 |
EdgeCore AGR420 |
74 |
10 |
Consolidated BNG Platforms
| Platform | Number of LAG Interfaces Supported | Number of LAG Members Supported |
|---|---|---|
UfiSpace S9500-22XST |
22 |
10 |
Edgecore CSR320 |
24 |
10 |
UfiSpace S9510-28DC |
NA |
NA |