# Dynamic IP Tunnel Overview

E Series routers support the following types of dynamic IP tunnels:

- Generic Routing Encapsulation (GRE) tunnels
- Distance Vector Multicast Routing Protocol (DVMRP) tunnels, also known as IP-in-IP tunnels

To establish a dynamic IP tunnel for GRE or DVMRP interfaces, you must configure a destination profile for a specific transport virtual router that is used to store tunnel configuration options, including the source and destination addresses of the dynamic IP tunnel.

A client application triggers the creation of dynamic IP tunnels based on the information stored in the GRE or DVMRP destination profile. The application specifies a tunnel source, tunnel destination, transport virtual router, and tunnel mode (GRE or DVMRP). If these parameters match those configured in the destination profile, the system creates the dynamic IP tunnel.

The application can automatically create an upper layer IPv4 interface over the GRE or DVMRP interface by using the IP characteristics defined in a profile referenced in the GRE or DVMRP destination profile.

## Data MDT for Multicast VPNs and Dynamic IP Tunnels

The data multicast distribution tree (MDT) application for multicast VPNs can create dynamic point-to-multipoint GRE tunnels.

The data MDT application enables you to solve the problem of IP routers flooding unnecessary multicast information to PE routers that have no interested receivers for a particular VPN multicast group. The multicast data MDT solution requires the creation of a new dynamic IP tunnel by the PE router if the source exceeds a configured rate threshold parameter.

The data MDT application supports a co-located tunnel interface. The base GRE interface and its co-located data MDT interface must be both static or both dynamic.

The data MDT application creates a dynamic IP tunnel using the attributes in a customized destination profile.

When creating the dynamic IP tunnel, the data MDT application assigns its name using the following format:

mvpn-dynamic-number

For the data MDT application, you should configure a customized destination profile. For information about configuring multicast VPNs using GRE tunnels, see Configuring PIM for IPv4 Multicast in JunosE Multicast Routing Configuration Guide.

## Mobile IP and Dynamic IP Tunnels

The Mobile IP application can create dynamic point-to-point GRE and DVMRP tunnels.

The Mobile IP application is a tunneling-based solution that enhances the utility of E Series Broadband Services Routers at the edge of the network between fixed wire and wireless network domains. This tunneling-based solution enables a router on a user's home subnet to intercept and forward IP packets to users while they roam beyond traditional network boundaries.

To achieve mobility, the mobile node takes a secondary IP address that matches the new network and redirects the traffic bound to the primary or home address to the mobile node's new network. In the Mobile IP feature, the two agents that accomplish this task are the home agent and the foreign agent.

The Mobile IP application can create a dynamic IP tunnel using the attributes in a default destination profile or a customized destination profile.

When creating the dynamic IP tunnel, the Mobile IP application assigns its name using the following format:

mobileIp-dynamic-number

When the Mobile IP application creates the dynamic IP tunnel, it sets a Don't Fragment bit in the packet and in the outer IP header.

The Mobile IP home agent uses the dynamic IP tunnel for routing loop detection. The home agent examines packets that are intercepted by the home agent and destined for the mobile node. If the packet is already encapsulated, and the inner destination address is the same as the outer destination address, then the system examines the outer source address. If the outer source address is the same as the tunnel destination address or the foreign agent care-of-address (CoA), the system silently discards the packet. In all other cases, the tunnel encapsulation is successful.

For more information about configuring Mobile IP using GRE or DVMRP tunnels, see Configuring the Mobile IP Home Agent .

## Combining Dynamic and Static IP Tunnels in the Same Chassis

You can configure both dynamic and static IP tunnels in the same chassis.

A tunnel pair consists of two endpoints; one side encapsulates and the other side decapsulates. You can create a tunnel pair with two statically configured endpoints, two dynamically created endpoints, or with one static and one dynamic endpoint.

When configuring IP tunnels, you must consider that a tunnel is uniquely defined by its tunnel source, tunnel destination, transport virtual router, and mode (GRE or DVMRP). The system does not allow multiple tunnels with the same parameters. For example, when you configure a static tunnel with the same parameters as an existing dynamic IP tunnel, the system does not create the dynamic IP tunnel.

## Changing and Removing Existing Dynamic IP Tunnels

You can modify the parameters in a destination profile referenced by existing dynamic IP tunnels. The changes only affect new dynamic IP tunnels that reference the destination profile.

You can relocate a dynamic IP tunnel for the Mobile IP application.

You cannot relocate a dynamic IP tunnel for the data MDT application because it is created using a profile. The system deletes dynamic IP tunnels that are relocated. Connections between a static tunnel endpoint and a dynamic tunnel endpoint can fail if the dynamic tunnel endpoint is deleted.

The client application removes dynamic IP tunnel interfaces when one of the following situations occur:

- The transport virtual router is removed.
- The tunnel interface relocates and the tunnel had an IP interfaced stacked on it.
- The tunnel interface indicates that setup is complete when the system is warm started, but it has no upper IP interface.