What is multipoint GRE?

Generic Routing Encapsulation (GRE) is a tunneling protocol that can encapsulate a number of OSI layer 3 protocols. This protocol can be used by two endpoints to communicate with each other. Multipoint GRE (mGRE) is a protocol that can be used to enable one node to communicate with many nodes.

What is IPSec GRE used for?

The IP Security (IPsec) Protocol is a standards-based method of providing privacy, integrity, and authenticity to information transferred across IP networks. GRE is used when IP packets need to be sent from one network to another, without being parsed or treated like IP packets by any intervening routers.

How is a multi point GRE tunnel configured?

Multipoint tunnels are configured only on the hub router. The traditional implementation of a GRE tunnel involved the configuration of a point-to-point tunnel going between two sites. This type of configuration works well when this is the behavior and there are a limited number of tunnels that need to be configured.

Can a multipoint GRE be used for multiple destinations?

Thing will get messy quickly…we have to create multiple tunnel interfaces, set the source/destination IP addresses etc. It will work but it’s not a very scalable solution. Multipoint GRE, as the name implies allows us to have multiple destinations. When we use them, our picture could look like this:

How does NhRP work with multipoint GRE?

The NHRP server keeps track of all public IP addresses in its cache. When one router wants to tunnel something to another router, it will request the NHRP server for the public IP address of the other router. Since NHRP uses this server and clients model, it makes sense to use a hub and spoke topology for multipoint GRE.

How to configure dynamic multipoint VPN using GRE over IPsec?

Current configuration : 1827 bytes ! version 12.3 service config service timestamps debug datetime msec service timestamps log datetime msec no service password-encryption ! hostname sv9-2 ! boot-start-marker boot-end-marker ! enable password cisco ! no aaa new-model ip subnet-zero ! ! no ip domain lookup ! ip ssh break-string ! !—