Link Aggregation and Port Trunking


To ensure that your business can keep up with the port and bandwidth demands of a growing network, you can employ Link Aggregation to increase bandwidth for DrayTek VigorSwitch switches.

What is Link Aggregation?

Link Aggregation Control Protocol (LACP) is also known as the networking standard IEEE 802.3ad, an industry standard system for grouping network ports and adapters to operate together.

It allows aggregated traffic coming from several interfaces to be sent through a single logical link, which is commonly referred to as a Link Aggregation Group (LAG).
Along with the increase in speed, this inexpensive solution also benefits from resiliency. If one of the LAG bundled interfaces or cables fails, others can still provide the connection.

Link Aggregation increases the total available bandwidth, sharing load across multiple LAN ports, similar to using Load Balancing on a DrayTek Vigor router to increase Internet bandwidth. This helps to avoid bottlenecks causing slow traffic, where a single Gigabit link may not be enough to handle all traffic between switches.

vigorswitch lacp1

Why use Link Aggregation?

The image below depicts a common physical topology where dozens or hundreds of clients need to 'talk' to other network segments and servers. Link Aggregation has not been deployed yet. Network administrators may notice that some improvements are necessary if it's found that the single link between the two switches is a bottleneck to bandwidth.

congested traffic - no LACP

Traffic generated may greatly exceed the available physical link throughput between the local switches. It is possible to use faster interfaces available on VigorSwitch models such as G2280x or P2280x, which have 10Gb connectivity (and also supports LACP), or use your existing 1Gb Vigor switches. Deploying Link Aggregation setup should help with a bottleneck effect on busy networks and have a positive impact on network resilience.

As illustrated below there are LAGs (Link Aggregation Groups) configured on the switches. Several physical ports are bundled together to form a single logical interface. If one of the physical links fails, other(s) will still provide connection between the switches. With two or more interfaces used for a LAG, the traffic between them will be load balanced and should benefit the bandwidth.

aggregated traffic load-balanced by LACP logical links

See the Configuration Requirements section for a list of conditions required to apply LACP (802.3ad) that should be met before selected interfaces will form a new Link Aggregation Group.

Configuration Requirements

  •  Use compatible devices that can handle LACP; the table below lists some of the LACP capable DrayTek VigorSwitches:

Applicable Products

VigorSwitch Switches 
VigorSwitch P1092 VigorSwitch G1080
VigorSwitch P1280 VigorSwitch G1280
VigorSwitch P2280 VigorSwitch G2280
VigorSwitch P2280x VigorSwitch G2280x
VigorSwitch P2500 VigorSwitch G2500
VigorSwitch P2121  
  • Make sure that your selected interfaces operate at the same speed (eg. don't mix ports with 10Gbps and ports with 1Gbps into the same LAG group).
  • Use the same duplex mode.
  • Up to 8 compatible Ethernet interfaces can be grouped to create one LAG.
  • Check if your bundled interfaces are assigned to the same VLAN(s). If one of them is configured as trunk, the other side interfaces must also be configured as trunks.

Did you know?

LACP is part of the 802.3ad standard. Because it is provided by IEEE, it can be facilitated in multivendor environments.
Link Aggregation is also possible on Servers and Network Attached Storage with multiple Ethernet adapters. LAGs can be created between two switches or between a switch and the LACP-enabled server / NAS.
The same LAG cannot send traffic from one switch to two different switches. Create two or more LAGs when connecting with multiple devices.
LACP can negotiate the speed, duplex mode to make sure that both sides are compatible. Just choose the 'Auto' or similar option if supported by your devices.
Load balancing can use one of the following modes: source MAC to destination MAC (OSI layer 2) which balances traffic for different MAC addresses; or source IP/MAC to destination IP/MAC across the physical links (OSI layers 3 & 2) which balances traffic both for different IP addresses (or by MAC address for non TCP/IP packets).We recommend to use "IP & MAC Address" as the load balancing method because this allows Router, Internet & VPN traffic to be considered when assigning a link to a new session.
LAG bundles multiple physical links together and is seen as one logical link. When several LAG groups exist between two devices, Spanning Tree (STP) will block one of them to prevent switching loops.