MPLS VPN L3VPN over GRE
MPLS VPN--L3VPN over GRE
Last Updated: July 23, 2012
The MPLS VPN--L3VPN over GRE feature provides a mechanism for tunneling Multiprotocol Label Switching (MPLS) packets over a non-MPLS network. This feature utilizes MPLS over generic routing encapsulation (MPLSoGRE) to encapsulate MPLS packets inside IP tunnels. The encapsulation of MPLS packets inside IP tunnels creates a virtual point-to-point link across non-MPLS networks.
Finding Feature Information
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Prerequisites for MPLS VPN--L3VPN over GRE
Restrictions for MPLS VPN--L3VPN over GRE
The MPLS VPN--L3VPN over GRE feature does not support the following:
Information About MPLS VPN--L3VPN over GRE
Overview of MPLS VPN-L3VPN over GRE
The MPLS VPN--L3VPN over GRE feature provides a mechanism for tunneling MPLS packets over non-MPLS networks. This feature allows you to create a GRE tunnel across a non-MPLS network. The MPLS packets are encapsulated within the GRE tunnel packets, and the encapsulated packets traverse the non-MPLS network through the GRE tunnel. When GRE tunnel packets are received at the other side of the non-MPLS network, the GRE tunnel packet header is removed and the inner MPLS packet is forwarded to its final destination.
The provider-edge-to-provider-edge (PE-to-PE) tunneling configuration provides a scalable way to connect multiple customer networks across a non-MPLS network. With this configuration, traffic that is destined to multiple customer networks is multiplexed through a single GRE tunnel.
As shown in the figure below, the PE devices assign VPN routing and forwarding (VRF) numbers to the customer edge (CE) devices on each side of the non-MPLS network.
The PE devices use routing protocols such as Border Gateway Protocol (BGP), Open Shortest Path First (OSPF), or Routing Information Protocol (RIP) to learn about the IP networks behind the CE devices. The routes to the IP networks behind the CE devices are stored in the associated CE device's VRF routing table.
The PE device on one side of the non-MPLS network uses the routing protocols (that operate within the non-MPLS network) to learn about the PE device on the other side of the non-MPLS network. The learned routes that are established between the PE devices are then stored in the main or default routing table.
The opposing PE device uses BGP to learn about the routes that are associated with the customer networks that are behind the PE devices. These learned routes are not known to the non-MPLS network.
The following figure shows BGP defining a static route to the BGP neighbor (the opposing PE device) through the GRE tunnel that spans the non-MPLS network. Because routes that are learned by the BGP neighbor include the GRE tunnel next hop, all customer network traffic is sent using the GRE tunnel.
As shown in the figure below, the provider-to-provider-edge (P-to-PE) tunneling configuration provides a way to connect a PE device (P1) to an MPLS segment (PE-2) across a non-MPLS network. In this configuration, MPLS traffic that is destined to the other side of the non-MPLS network is sent through a single GRE tunnel.
As shown in the figure below, the provider-to-provider (P-to-P) configuration provides a method of connecting two MPLS segments (P1 to P2) across a non-MPLS network. In this configuration, MPLS traffic that is destined to the other side of the non-MPLS network is sent through a single GRE tunnel.
How to Configure MPLS VPN--L3VPN over GRE
Configuring the MPLS VPN--L3VPN over GRE Tunnel Interface
To configure the MPLS VPN--L3VPN over GRE feature, you must create a GRE tunnel to span the non-MPLS networks. You must perform the following procedure on the devices located at both ends of the GRE tunnel.
Example: Configuring a GRE Tunnel that spans a non-MPLS Network
The following example shows a GRE tunnel configuration that spans a non-MPLS network. This example shows the tunnel configuration on the PE devices (PE1 and PE2) located at both ends of the tunnel:
Device# configure terminal Device(config)# interface Tunnel 1 Device(config-if)# ip address 10.1.1.1 255.255.255.0 Device(config-if)# tunnel source 10.0.0.1 Device(config-if)# tunnel destination 10.0.0.2 Device(config-if)# mpls ip
Configuration Examples for MPLS VPN--L3VPN over GRE
Example: MPLS Configuration with MPLS VPN--L3VPN over GRE
The following basic MPLS configuration example uses a GRE tunnel to span a non-MPLS network. This example is similar to the configuration shown in the first figure above.
! mpls ip ! ip vrf vpn1 rd 100:1 route-target import 100:1 route-target export 100:1 ! interface loopback 0 ip address 10.2.2.2 255.255.255.255 ! interface GigabitEthernet 0/1/2 ip address 10.1.1.1 255.255.255.0 ! interface Tunnel 1 ip address 10.0.0.1 255.255.255.0 tunnel source 10.1.1.1 tunnel destination 10.1.1.2 mpls ip ! interface GigabitEthernet 0/1/3 ip vrf forwarding vpn1 ip address 10.10.0.1 255.255.255.0 ! router bgp 100 neighbor 10.5.5.5 remote-as 100 neighbor 10.5.5.5 update-source loopback0 ! address-family vpnv4 neighbor 10.5.5.5 activate neighbor 10.5.5.5 send community-extended ! address-family ipv4 vrf vpn1 neighbor 10.10.0.2 remote-as 20 neighbor 10.10.0.2 activate !
! mpls ip ! ip vrf vpn1 rd 100:1 route-target import 100:1 route-target export 100:1 ! interface loopback 0 ip address 10.5.5.5 255.255.255.255 ! interface GigabitEthernet 0/1/1 ip address 10.1.1.2 255.255.255.0 ! interface Tunnel 1 ip address 10.0.0.2 255.255.255.0 tunnel source 10.1.1.2 tunnel destination 10.1.1.1 mpls ip ! interface GigabitEthernet 0/0/5 ip vrf forwarding vpn1 ip address 10.1.2.1 255.255.255.0 ! router bgp 100 neighbor 10.2.2.2 remote-as 100 neighbor 10.2.2.2 update-source loopback0 ! address-family vpnv4 neighbor 10.2.2.2 activate neighbor 10.2.2.2 send community-extended ! address-family ipv4 vrf vpn1 neighbor 10.1.2.2 remote-as 30 neighbor 10.1.2.2 activate !
Feature Information for MPLS VPN--L3VPN over GRE
The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.
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