Aggregated Ethernet Overview

Link aggregation of Ethernet interfaces is defined in the IEEE 802.3ad standard. The JUNOS Software implementation of 802.3ad balances traffic across the member links within an aggregated Ethernet bundle based on Layer 3 or Layer 4 (or both) information carried in the packet or based on session ID data. (The session ID data has higher precedence than the Layer 3 or 4 information.) This implementation uses the same load-balancing algorithm used for per-packet load balancing.

You can combine multiple physical Ethernet ports to form a logical point-to-point link, known as a link aggregation group (LAG) or bundle. Support for LAGs based on IEEE 802.3ad makes it possible to aggregate physical interface links on your device. LAGs provide increased interface bandwidth and link availability by linking physical ports and load-balancing traffic crossing the combined interface.

In a chassis cluster configuration, link aggregation allows a redundant Ethernet interface to add multiple child interfaces from both nodes and thereby create a redundant Ethernet interface link aggregation group (LAG).

Link aggregation allows one or more links to be combined together to form a LAG, such that a media access control (MAC) client can treat the LAG as if it were a single link. For the LAG to operate correctly, it is necessary to coordinate the two end systems connected by the LAG, either manually or automatically.

Internally, a LAG is a virtual interface presented on SRX3000 and SRX5000 line devices or on any system (consisting of devices such as routers and switches) supporting 802.3ad link aggregation. Externally, a LAG corresponds to a bundle of physical Ethernet links connected between an SRX3000 or SRX5000 line device and another system capable of link aggregation. This bundle of physical links is a virtual link.

JUNOS Software supports the Link Aggregation Control Protocol (LACP), which is a subcomponent of IEEE 802.3ad. LACP provides additional functionality for LAGs.

LACP is supported in standalone (single chassis) deployments, where aggregated Ethernet interfaces are supported, and in chassis cluster deployments, where aggregated Ethernet interfaces and redundant Ethernet interfaces are supported simultaneously.

Aggregated Ethernet interfaces can be Layer 3 interfaces (VLAN-tagged or untagged) and Layer 2 interfaces. LACP is supported on Layer 3 only.

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