DMVPN

DMVPN (Dynamic Multipoint VPN) is a technique used to build scalable and secure VPNs over the internet or any untrusted network. 

Multicast support within DMVPN is achieved through the use of GRE (Generic Routing Encapsulation) tunnels and protocols like NHRP (Next Hop Resolution Protocol) for dynamic discovery of tunnel endpoints.

Enabling multicast over DMVPN involves additional configurations to support multicast traffic. 

Typically, protocols like PIM (Protocol Independent Multicast) Sparse Mode or Dense Mode are used for multicast routing over the DMVPN network. 

These protocols help in the distribution of multicast traffic efficiently among the tunnel endpoints.

To implement DMVPN with multicast support, you'd typically configure your devices to support multicast routing (using PIM), set up the GRE tunnels between sites, and ensure NHRP is properly functioning to manage the mapping between tunnel IP addresses and physical addresses.

Each site's router participating in the DMVPN network needs to be configured to support multicast routing and have the necessary configurations to ensure that multicast traffic can traverse the tunnels between sites.

To set up DMVPN with multicast support, here are the high-level steps and configuration components:

1. **Basic DMVPN Configuration:**

   - Configure the basic DMVPN setup using GRE tunnels and NHRP for dynamic discovery of tunnel endpoints.

   - Set up the hub and spoke topology, designating a hub router and connecting spoke routers.

2. **Enable Multicast Routing Protocol:**

   - Decide on a multicast routing protocol (PIM Sparse Mode or Dense Mode).

   - Enable multicast routing on the routers:

     - For PIM Sparse Mode:

       - Configure the router to support PIM on the interfaces connected to the DMVPN tunnels.

       - Designate a rendezvous point (RP) for the multicast group.

       - Enable sparse-mode on the tunnel interfaces.

     - For PIM Dense Mode:

       - Enable dense-mode on the tunnel interfaces.

   

3. **Tunnel Configuration:**

   - Ensure that the GRE tunnels support multicast traffic by configuring them appropriately.

   - Assign tunnel source and destination addresses.

   - Enable multicast-specific parameters on the tunnel interfaces, depending on the chosen multicast routing protocol.

4. **NHRP Configuration:**

   - Verify and ensure that NHRP is properly configured to resolve tunnel endpoint mappings.

Here's an example configuration snippet for PIM Sparse Mode on a Cisco router for multicast support over DMVPN:

```markdown

interface Tunnel0

 ip address 192.168.1.1 255.255.255.0

 ip pim sparse-mode

interface Tunnel1

 ip address 192.168.2.1 255.255.255.0

 ip pim sparse-mode

interface <outgoing interface>

 ip pim sparse-mode

ip multicast-routing

ip pim rp-address <RP address>

```

Replace `<outgoing interface>` with the appropriate interface connected to the DMVPN network and `<RP address>` with the actual address of the rendezvous point.

This configuration assumes two tunnels (Tunnel0 and Tunnel1) and enables PIM sparse-mode on those interfaces and the outgoing interface towards the DMVPN network.