Link aggregation (LAG) between two network devices allows your devices to treat multiple Ethernet links as if they were a single link to increase bandwidth or provide fault tolerance. 

This article explains how to set up link aggregation between a Smart Managed Pro Switch and a Synology NAS (DSM version 6.2-23511).

Set up LAG on the Smart Managed Pro switch.

1. Open a web browser on a computer that is connected to the same network as your switch or is connected to the switch directly through an Ethernet cable.
2. Enter your switch’s IP address in the address bar of your web browser, or use a saved bookmark to access your switch.
3. Enter your administrator password and press Enter.
   The default password is password.
   The home page displays.
4. Select Switching - LAG - Basic - LAG Configuration.
5. Select the checkbox beside the LAG that you want to set up.
   If LAG ID 1 is not already configured, select LAG ID 1.
6. Ensure Admin Mode is set to Enable.
7. Set LAG Type to LACP.
8. Click Apply.
9. Click LAG Membership.
10. In the LAG ID dropdown menu, choose the LAG ID that you configured in step 5.
11. Click each port that you want to make a member of the LAG.
12. Click Apply.

Set up LAG on the Synology NAS.

1. Log in to the admin page of your Synology NAS.
2. Select Control Panel - Connectivity - Network.
3. Select Network Interface - Create - Create Bond.

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4. Select IEEE802.3ad Dynamic Link Aggregation.

5. Click Next.
6. Click each port that you want to make a member of the LAG on the NAS.

7. Click Next.
8. Select whether to use a DHCP assigned or fixed IP address on the LAG.
9. Click Apply.

Connect the ports that you made members of the LAG on the switch to the ports that are members of the LAG on the Synology NAS.

Note: All ports that participate in a LAG (that is, the ports on both devices) must use the same port speed and duplex mode. It is recommended that the ports are configured for auto-negotiation.