Understanding Chassis Cluster Redundant Ethernet Interface Link Aggregation Groups

Support for Ethernet link aggregation groups (LAGs) based on IEEE 802.3ad makes it possible to aggregate physical interfaces on a standalone device. LAGs on standalone devices provide increased interface bandwidth and link availability. Aggregation of links in a chassis cluster allows a redundant Ethernet interface to add more than two physical child interfaces thereby creating a redundant Ethernet interface LAG. An redundant Ethernet interface LAG can have up to eight links per redundant Ethernet interface per node (for a total of 16 links per redundant Ethernet interface).

The aggregated links in a redundant Ethernet interface LAG provide the same bandwidth and redundancy benefits of a LAG on a standalone device with the added advantage of chassis cluster redundancy. A redundant Ethernet interface LAG has two types of simultaneous redundancy. The aggregated links within the redundant Ethernet interface on each node are redundant; if one link in the primary aggregate fails, its traffic load will be taken up by the remaining links. If enough child links on the primary node fail, the redundant Ethernet interface LAG can be configured so that all traffic on the entire redundant Ethernet interface fails over to the aggregate link on the other node.

Aggregated Ethernet interfaces, known as local LAGs, are also supported on either node of a chassis cluster but cannot be added to redundant Ethernet interfaces. Local LAGs are indicated in the system interfaces list using an ae- prefix. Likewise any child interface of an existing local LAG cannot be added to a redundant Ethernet interface and vice versa. Note that it is necessary for the switch (or switches) used to connect the nodes in the cluster to have a LAG link configured and 802.3ad enabled for each LAG on both nodes so that the aggregate links will be recognized as such and correctly pass traffic. The total maximum number of combined individual node LAG interfaces (ae) and redundant Ethernet (reth) interfaces per cluster is 128.

Note: The redundant Ethernet interface LAG child links from each node in the chassis cluster must be connected to a different LAG at the peer devices. If a single peer switch is used to terminate the redundant Ethernet interface LAG, two separate LAGs must be used in the switch.

Links from different PICs or IOCs and using different cable types (for example, copper and fiber-optic) can be added to the same redundant Ethernet interface LAG but the speed of the interfaces must be the same and all interfaces must be in full duplex mode. It is, however, for purposes of reducing traffic processing overhead, recommended that interfaces from the same PIC or IOC be used whenever feasible. Regardless, all interfaces configured in a redundant Ethernet interface LAG will share the same virtual MAC address.

Redundant Ethernet interface configuration also includes a minimum-links setting that allows you to set a minimum number of physical child links on the primary node in a given redundant Ethernet interface that must be working for the interface to be up. The default minimum-links value is 1. Note that the minimum-links setting only monitors child links on the primary node. Redundant Ethernet interfaces do not use physical interfaces on the backup node for either ingress or egress traffic.

Please note the following support details:

Quality of service (QoS) is supported in a redundant Ethernet interface LAG. Guaranteed bandwidth is, however, duplicated across all links. If a link is lost, there is a corresponding loss of guaranteed bandwidth.
Layer 2 transparent mode and Layer 2 security features are supported in redundant Ethernet interface LAGs.
Link Aggregation Control Protocol (LACP) is supported in chassis cluster deployments, where aggregated Ethernet interfaces and redundant Ethernet interfaces are supported simultaneously.
Chassis cluster management, control, and fabric interfaces cannot be configured as redundant Ethernet interface LAGs or added to a redundant Ethernet interface LAG.
Network processor bundling can coexist with redundant Ethernet interface LAGs on the same cluster. However, assigning an interface simultaneously to a redundant Ethernet interface LAG and a network processor bundle is not supported.
Single flow throughput is limited to the speed of a single physical link regardless of the speed of the aggregate interface.

Note: For more information about Ethernet interface link aggregation and LACP, see the “Aggregated Ethernet” chapter of the JUNOS Software Interfaces Configuration Guide for Security Devices.

Understanding Chassis Cluster Redundant Ethernet Interface Link Aggregation Groups

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