---
title: 'Tutorial: Allow UDP Multicast and IGMP to Pass Through'
canonical: https://openvpn.net/as-docs/v3/tutorials/tutorial--udp-multicast-and-igmp-allowed/
product: Access Server Docs
description: Access Server transfers information by unicast. Follow these steps to change this and allow UDP multicast and IGMP to pass through.
---

# Tutorial: Allow UDP Multicast and IGMP to Pass Through

## Overview

This tutorial guides you through switching from unicast (Access Server's default data transfer) to allowing UDP multicast and IGMP. This is done with the configuration key, **vpn.routing.allow\_mcast**.

Access Server blocks multicast or broadcast traffic. Follow these steps to lift that restriction.

## Prerequisites

- An installed Access Server.
- Console access and the ability to get root access.

## Step 1: Allow UDP multicast and IGMP to pass through

1. Connect to the console and get root privileges.
2. Allow UDP multicast and IGMP traffic to pass through:

   ```
   sacli --key "vpn.routing.allow_mcast" --value "true" ConfigPut
   sacli start
   ```

   - This setting implements these iptables rules on the VPN server, which is what allows the traffic to pass through:

     ```
     ACCEPT udp   -- anywhere  base-address.mcast.net/4 udp
     ACCEPT igmp  -- anywhere  anywhere
     ACCEPT udp   -- anywhere  base-address.mcast.net/4 udp
     ACCEPT igmp  -- anywhere  anywhere
     ```
3. To restore the default setting (and again restrict UDP multicast and IGMP traffic):

   ```
   sacli --key "vpn.routing.allow_mcast" ConfigDel
   sacli start
   ```

---

Prev: [Tutorial: Managing iptables Settings in Access Server](https://openvpn.net/as-docs/v3/tutorials/tutorial--manage-iptables.md)
Next: [Tutorial: Forward Multicast Traffic Between VPN Clients Across Multiple Daemons in Access Server](https://openvpn.net/as-docs/v3/tutorials/tutorial--multicast-routing-vpn-clients.md)
Index: https://openvpn.net/as-docs/llms.txt