How to Wire a Network Aggregate Switch

How to Wire a Network Aggregate Switch

Network aggregate switches combine multiple Ethernet links into a single logical interface for increased bandwidth and redundancy. They can be used to connect a single switch to another switch, a server, or a multiport WiFi access point, allowing for increased throughput between devices and greater fault tolerance.

To wire a network aggregate switch, you must configure the physical and logical interfaces in the correct order. The first step is to define the logical aggregated interface and its member links, which are also called member ports. Next, you must configure the Link Aggregation Control Protocol (LACP).

For Junos OS Evolved and Junos OBE software, you can configure LACP at the global level on a switch or for a specific aggregated Ethernet interface. When you configure LACP, the switch enables traffic to be sent across links that are configured into primary and backup subgroups. This provides traffic protection for links in the bundle during switchover events, such as link failures.

If you add a new member link to an aggregated Ethernet interface that is protected by LACP, the system selects it from the other member links and assigns it the highest priority. The link is referred to as the active link and is used to send and receive traffic until a switchover event occurs, such as a link failure.

When a switch fails and traffic destined for the LAG is carried over its remaining member links, this increases total bandwidth through the chassis. However, if a link fails that is not part of the LAG, a redistribution of traffic over remaining local links can occur resulting in reduced throughput to those links.

You can use the Revertive statement in the [edit interfaces] aggregated-ethernet-options lacp hierarchy to override the nonrevertive setting for an aggregated Ethernet interface if you have previously assigned the link to a static LAG. When the link is added to a dynamic LAG, the switch performs a recalculation of priority and then changes from the existing active to the new active link.

This recalculation can cause the system to send and receive traffic over a link that has been in a standby state for a long time, potentially causing data loss. To prevent this, you must enable the Revertive statement and ensure that the LACP is enabled on both ends of the aggregator before adding a new link to the aggregator.

In addition, you must ensure that both the active and the backup member links are configured with LACP on both endpoints to enable traffic from the two links in the aggregated Ethernet interface to be sent back to the vendor device that manages the interface. Otherwise, the vendor device will not be able to handle the traffic coming from the interface.

For example, if you have an aggregated Ethernet interface that contains two 10-Gigabit Ethernet links and a third port. You must connect the other port of each interface to the same switch and configure the two switches to form a link aggregation group.

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