LACP Link Aggregation

Nathan Hill-Haimes


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    LACP is a useful bonded broadband tool for upgrading your link aggregation group (LAG). Here's everything you need to know.

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    What is LACP and how can I use it in my network?

    Link aggregation is a setup that enables the combination of two or more Ethernet lines into one logical link between a pair of networked devices. There are various other names for link aggregation, like Ethernet bonding, NIC teaming and port channelling. Frequently-used combinations of devices include connecting a switch to:

    • A multi-port access point
    • A network attached storage (NAS) device
    • Another switch

    Both network hardware and management tools treat a link aggregation group (LAG) consisting of two or more Ethernet connections as one link. For instance, you could add a LAG to a virtual local area network (VLAN), or configure multiple LAGs on a single switch. There are network devices that have support for Link Aggregation Control Protocol (LACP), and this is helpful in preventing faults in the process of setting up link aggregation.

    Why do people use link aggregation?

    There are several advantages of using link aggregation:

    • It increases bandwidth - With aggregated physical links, you get a higher overall bandwidth than each individual link can offer.
    • It uses physical resources more efficiently - You can balance the load of traffic across the multiple links.
    • It makes the link aggregation more reliable and available - If any of the physical links in the LAG develops a fault, traffic is reassigned to the remaining links in a dynamic and transparent way.
    • It is cost-effective - It can be expensive to invest in a network upgrade, particularly where new cable runs are required. With link aggregation, you increase bandwidth without having to purchase new equipment.

    The two primary forms of LAGs are dynamic and static. Dynamic LAGs leverage Link Aggregation Control Protocol (LACP) to monitor configurations between the two devices connected through link aggregation.

    Some devices work with static LAGS but not dynamic ones with LACP. Your product's manual should state whether LACP is supported. Linux-based devices frequently offer a range of additional link aggregation types. These offer benefits like load balancing and increased fault tolerance.


    What exactly is Link Aggregation Control Protocol?

    Link Aggregation Control Protocol (LACP) is one of the IEEE standards. It enables devices to send Link Aggregation Control Protocol Data Units (LACPDUs) to one another to forge a connection via link aggregation.

    It will still be necessary to handle the link aggregation configuration on both devices. Still, with LACP, you have a tool to help avoid a prevalent problem when working on link aggregation: configuration errors in the LAG settings. When the devices detect that they can't establish a link aggregation connection, they won't try to establish one. You will see that the link is down on the admin control panel.

    An additional helpful benefit of LACP is when a member link ceases to send the LACPDUs. Perhaps because the cable has been unplugged, LAG automatically removes that link; this minimises packet loss.

    You will need two devices that both support LACP to establish a dynamic LAG between them. It is recommended always to do this when you have two devices that support LACP.

    How can link aggregation be set up for my network?

    The following set of instructions is a generic process for setting up link aggregation involving two devices from your network. If you need specific information that pertains to link aggregation for the devices you have, check out the support pages of your product. You can usually find this on the manufacturer's website. If not, try contacting them and asking for advice.

    Setting up link aggregation between a pair of devices in your network requires the following process:

    1. Verify that the two devices can accommodate link aggregation.

    2. Modify the LAG settings on each device.

    3. Ensure the LAG you set up on the two devices has matching settings for duplex mode, port speed, MTU size (sometimes known as jumbo frames) and flow control.

    4. Be sure that all ports involved in the LAG have memberships to the same VLAN. A VLAN can have a LAG added by configuring the LAG and then adding it; don't add the individual ports.

    A WORD OF ADVICE: Don't link the devices to one another with two or more Ethernet cables until after the LAG is set up on both devices. These will slow, or even stop, regular traffic through your network. Establishing numerous connections between two devices with loop prevention can result in a network loop.

    5. Take note of the ports on the devices you add to the LAG and be sure you only connect those ports. If the port members do not match or are not members of the LAG, the LAG will reject the configuration.

    6. Using Ethernet or fibre cable, connect the ports on each device assigned to the LAG.

    7. Check that the LEDs for all connected ports are flashing green.

    8. Look in the admin control panel for both devices; the link status should say 'UP'.

    Once you overcome the hurdle of setting it up, LACP is a powerful tool that could hugely benefit your business.

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