What Functionality Does MGRE Provide to the DMVPN Technology?

MGRE is a key component to the DMVPN technology. It provides the functionality of creating a virtual private network (VPN) over the public Internet.

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Introduction

Multipoint Generic Routing Encapsulation (MGRE) is a Cisco IOS generic routing encapsulation (GRE) tunneling protocol that supports multipoint applications. It is the key component of Cisco’s Dynamic Multipoint VPN (DMVPN) technology. In this article, we will take a closer look at the MGRE functionality and how it relates to the DMVPN technology.

MGRE was designed to address the following main problems with GRE:

– Lack of support for multicast traffic
– Lack of support for multiple logical tunnels between the same endpoints
– Inefficiencies associated with GRE keepalives

Multicast traffic support is essential for many applications, such as video conferencing and streaming media. The ability to carry multiple logical tunnels over a single physical tunnel can be important in certain situations, such as when you want to segregate traffic between different departments or user groups. The efficiency improvements in GRE keepalives can be important in large-scale deployments.

What is DMVPN?

DMVPN is a Cisco technology that enables the creation of a secure IP network. It allows for dynamic creation of point-to-point tunnels between network devices, allowing for greater flexibility and scalability than traditional VPNs. DMVPN also supports multicast traffic, making it ideal for applications such as video conferencing and streaming media. MGRE (Multipoint GRE) is a key component of DMVPN, providing the ability to create multiple GRE tunnels between spoke devices.

The Benefits of DMVPN

The Multi-GRE (MGRE) function is a key component of Cisco’s DMVPN technology. MGRE provides many benefits to the DMVPN deployment, including:

– Reduced CPU and memory usage on hub and spoke routers
– Ability to support larger numbers of spoke routers
– Improved scalability
– Increased flexibility in spoke-to-spoke tunnel configuration
– Reduced administrative overhead

How DMVPN Works

Multipoint GRE (MGRE) is a Cisco GRE tunnels solution for creating large-scale VPNs. It is the foundation for Cisco Dynamic Multipoint VPN (DMVPN), a solution that significantly reduces configuration complexity and deployment time.

DMVPN combines GRE tunnels, mGRE, Next Hop Resolution Protocol (NHRP), and IPsec encryption to create hub-and-spoke or mesh topologies. These topologies provide flexibility and can be deployed quickly.

The Different Types of DMVPN

DMVPN comes in 3 different types: Hub and Spoke, Full Mesh, and Hybrid. The first, Hub and Spoke DMVPN, is the most common and it connects spoke routers to a central hub router. All data must go through the hub router, so if the hub router goes down, then the entire network does as well.

The second type is Full Mesh DMVPN which overcomes this by creating a direct tunnel between each router. So if one fails, there are still others that can take its place. The disadvantage of this type is that it requires a higher number of tunnels which takes up more processing power.

The third and final type is Hybrid DMVPN which combines aspects of both Hub and Spoke and Full Mesh DMVPNs. It uses a partial mesh topology in which some routers are configured as spoke routers while others act as hub routers. This allows for more specific control over traffic while still providing some redundancy in case of failure.

The Key Components of DMVPN

In order to understand the functionality that MGRE provides to DMVPN, it is first necessary to understand the key components of DMVPN. DMVPN is based on three key technologies:

-Multipoint GRE (MGRE): this is the key component that allows multiple VPN sites to be connected together over a common IP network. MGRE encapsulates traffic from each site in a separate GRE tunnel.

-Spoke-to-Spoke Tunneling: this allows traffic to be routed directly between sites, without passing through the hub. This improves performance and reduces latency.

-Dynamic Routing: this allows routes to be automatically added and removed from the network as sites are added or removed. This makes the network much more scalable than traditional VPNs.

The Advantages of MGRE

When configuring Cisco DMVPN, you have the option to use either Next Hop Resolution Protocol (NHRP) or Multipoint GRE (MGRE). MGRE has some significant advantages over NHRP, which is the traditional GRE tunneling protocol used with DMVPN.

MGRE encapsulates the entire IP packet in a single GRE header. This has two main benefits. First, it allows the use of multiple protocols over the tunnel without the need for additional configuration, as each protocol can be identified by its own IP address. Second, it allows for easy troubleshooting of tunnel connectivity issues as all packets are visible in the GRE header.

In addition, MGRE supports multicast traffic natively. NHRP does not support multicast traffic, so a separate protocol such as Protocol Independent Multicast (PIM) must be deployed in order to take advantage of this feature.

Overall, MGRE provides a more robust and flexible solution than NHRP for Cisco DMVPN deployments.

The Disadvantages of MGRE

When it comes to Internet connectivity, there are a few different types of VPN technologies that can be used in order to provide a secure connection. One such technology is DMVPN, which uses the GRE protocol in order to create a tunnel between devices. However, one disadvantage of using GRE is that it does not support multicast traffic.

This is where MGRE comes in, as it provides support for multicast traffic by encapsulating it within the GRE tunnel. However, there are a few disadvantages to using MGRE which include:

– Increased CPU usage due to the need to process the extra encapsulated data
– Increased bandwidth usage due to the extra data that needs to be transmitted
– Potentially decreased security due to the extra layer of encapsulation

The Bottom Line

At the bottom line, MGRE provides the functionality of a multipoint GRE tunnel that can be used with a variety of Cisco IOS routers. This makes it an essential part of the DMVPN technology.

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