Link Aggregation Groups (LAG)

A Link Aggregation Group (LAG) — also known as a port channel or bond — is a method of combining multiple physical network links between two devices into a single logical interface. This increases total bandwidth between those devices and provides redundancy: if one link in the group fails, traffic automatically shifts to the remaining links without dropping the connection. LAGs are governed by the IEEE 802.3ad/LACP standard, which allows devices to negotiate and manage the aggregated links dynamically.

Use a LAG when a single uplink is a bottleneck or a single point of failure — common scenarios include switch-to-switch uplinks, server-to-switch connections for high-throughput workloads, and NAS or storage appliance connections where both speed and availability matter. For example, four 1G ports in a LAG yield up to 4Gbps of aggregate bandwidth while also providing fault tolerance. It's worth noting that LAGs distribute traffic across member links per-flow (not per-packet), so a single large transfer won't exceed the speed of one member link — the gains are realized across multiple concurrent connections.

LAG requires support on both ends of the connection — if one device doesn't support LACP or static aggregation, the LAG cannot be formed. Most managed switches, enterprise NICs, and modern operating systems support LAG natively, but consumer-grade hardware and some entry-level switches often do not. Before deploying a LAG, verify that both devices support the same aggregation mode (LACP dynamic vs. static/manual), as a mismatch will result in the links either failing to bond or causing network instability. When in doubt, check the datasheets for both devices and confirm the specific ports being used actually support aggregation — on some switches, LAG membership is restricted to certain port groups. Most switches also have an upper limit on the number of LAGs available. Alta Labs switches support up to 8 LAGs.
 

Link Aggregation Control Protocol (LACP)

LACP (Link Aggregation Control Protocol) is the IEEE 802.3ad standard protocol that automates the negotiation and management of a LAG between two devices. Rather than manually configuring which ports belong to a bond, LACP-enabled devices exchange control frames (called LACPDUs) to dynamically discover compatible links, agree on group membership, and continuously monitor link health. This makes LACP the preferred mode for most deployments — it handles link failures gracefully, prevents misconfiguration, and can automatically recover when a failed link comes back online.

LACP operates in two modes: active and passive. A device in active mode initiates LACP negotiation, while a device in passive mode waits to respond. For a LAG to form, at least one side must be set to active — two passive devices will never negotiate a bond. In practice, setting both devices to active is the safest and most common approach. The alternative to LACP is a static (or "on") LAG, where ports are manually forced into a bond with no negotiation protocol. Static LAGs can work when LACP isn't supported on one end, but they carry more risk: neither device can detect a misconfiguration or a unilateral link failure on the other side, which can lead to traffic blackholing.
 

How to Implement

Generally speaking, you want to configure the “far” side of the link first as it’s not uncommon to lose communication with the far side while getting the configuration set up. As an example, let’s say we’re wanting to set up a LAG for a NAS that is connected to an S24-PoE. The “far” side of this setup would be the NAS. By configuring the NAS first, if the link drops, you can still configure the S24-PoE to get communication working again for the NAS.

If you’re new to LAGs, it is recommended to leave one interface excluded from the LAG on both sides. For example, let’s say we have 4 interfaces and we’re trying to create a LAG; start with just 3 interfaces and leave the 4th connected. This way, if communication is interrupted from the LAG standpoint, you still have that back up connection. Once you have the LAG set up and proper communication over the 3 interfaces, it’s typically not difficult to add the 4th connection into the LAG after the fact.
 

Once you’ve set up the client, then you set up the switch.

1. Login to https://manage.alta.inc
2. Click the Network tab
3. Click the icon of the switch you’ll be creating the LAG on
4. Select any interface that will be part of the LAG
5. Click Mode
6. In Combine, supply all interface numbers that will be part of the LAG
   1. On the S48-APOE, the SFP ports S1-S4 are numbered 49-52, for this option
7. Click Save

After clicking Save, note that there is a new icon on all interfaces that you specified. This gives you the ability to rapidly identify interfaces that are part of a LAG from the Switch pane view

Client Configurations - Advanced

Some clients expose additional features to have more granular control over how traffic is distributed within the LAG. Here are some examples to help you better understand what each means. Please note that some manufacturers may refer to these options by different terminology. We will use the terminology outlined in the 802.3ad standard

• broadcast - Transmits the same network packets to all the network interface cards.
• balance-tlb - The outgoing network packet traffic is distributed according to the current load (computed relative to the speed) on each network interface slave. Incoming traffic is received by one currently designated slave network interface. If this receiving slave fails, another slave takes over the MAC address of the failed receiving slave.
• balance-alb - The receive load balancing is achieved by ARP negotiation. The bonding driver intercepts the ARP Replies sent by the local system on their way out and overwrites the source hardware address with the unique hardware address of one of the NIC slaves in the single logical bonded interface such that different network-peers use different MAC addresses for their network packet traffic.
• balance-rr - Transmits network packets sequentially to each network interface card in order to distribute the internet traffic among all the NICs.
• balance-xor - Transmits network packets using the XOR algorithm, which selects the same NIC slave for each destination MAC address.
• 802.3ad Dynamic (LACP) - Uses a complex algorithm to aggregate NICs and configure speed and duplex settings, providing load balancing and fault tolerance.