Table Of Contents
MPLS VPN over mGRE
First Published: November 20, 2009Last Updated: September 20, 2011
The MPLS VPN over mGRE feature overcomes the requirement that a carrier support multiprotocol label switching (MPLS) by allowing you to provide MPLS connectivity between networks that are connected by IP-only networks. This allows MPLS label switched paths (LSPs) to use generic routing encapsulation (GRE) tunnels to cross routing areas, autonomous systems, and internet service providers (ISPs). when MPLS VPNs are configured over multipoint GRE (mGRE) you can deploy layer-3 (L3) provider edge (PE) based virtual private network (VPN) services using a standards-based IP core. This allows you to provision the VPN services without using the overlay method.
You can configure mGRE tunnels to create a multipoint tunnel network that overlays an IP backbone. This overlay connects PE routers to transport VPN traffic. In addition, when MPLS VPNs are configured over mGRE you can deploy L3 PE-based VPN services using a standards-based IP core. This allows you to provision the VPN services without using the overlay method. When MPLS VPN over mGRE is configured, the system uses IPv4-based mGRE tunnels to encapsulate VPN-labeled IPv4 and IPv6 packets between PEs.
Finding Feature Information
Your software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the "Feature Information for MPLS VPN over mGRE" section.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
Prerequisites for MPLS VPN over mGRE
Before you configure MPLS VPN with mGRE tunnels, ensure that the MPLS VPN is configured and working properly. See the "Configuring MPLS Layer 3 VPNs" module for information about setting up MPLS VPNs.
Restrictions for MPLS VPN over mGRE
•MPLS VPN over mGRE is supported on the Cisco 7600 series routers using the ES-40 line card and the SIP 400 line card as core facing cards.
•Tunnelled tag traffic must enter the router through a line card that supports MPLS VPN over mGRE.
•Each PE router supports one tunnel configuration only.
•MPLS VPN over mGRE does not support the transportation of multicast traffic between VPNs.
•When a GRE tunnel has the same destination address and source address as the mGRE, the tunnel gets route-cache switched.
•The packets that require fragmentation get route cache-switched.
•When an L3VPN profile is removed and added back, then you should clear the Border Gateway Protocol (BGP) using the clear ip bgp soft command.
•When an mGRE tunnel is created, a dummy tunnel is also created.
•The loopback or IP address used in the update source of the BGP configuration should be the same as that of the transport source of the L3VPN profile.
•mGRE is not stateful switchover (SSO) compliant. However, both mGRE and SSO coexist.
•mGRE and multicast distribution tree (MDT) tunnel should not be configured with the same loopback address.
The limitations for MPLS VPN over mGRE feature are as follows:
–Not all GRE options are supported in the hardware (for example, GRE extended header and GRE key).
–Checking identical VLANs (Internet Control Message Protocol [ICMP] redirect) is not supported on the tunnels.
–Features such as unicast reverse path forwarding (uRPF) and BGP policy accounting are not supported on the tunnels.
Information About MPLS VPN over mGRE
MPLS VPN over mGRE
GRE is a point-to-point tunneling protocol where two peers form the endpoints of the tunnel. It is designed to encapsulate network-layer packets inside IP tunneling packets. mGRE is a similar protocol with a single endpoint at one side of the tunnel connected to multiple endpoints at the other side of the tunnel. The mGRE tunnel provides a common link between branch offices that connect to the same VPN. Because mGRE is a point-to-multipoint model, fully meshed GRE tunnels are not required to interconnect MPLS VPN PE devices.
MPLS is a widely deployed VPN internet architecture. MPLS requires that all core routers in the network support MPLS. This feature is useful in networks where the service provider uses a backbone carrier to provide connectivity.
The MPLS VPN over mGRE feature overcomes the requirement of carrier support MPLS by allowing you to provide MPLS connectivity between networks that are connected by IP-only networks. This allows MPLS LSPs to use GRE tunnels to cross routing areas, autonomous systems, and ISPs.
When MPLS VPNs are configured over mGRE you can deploy L3 PE-based VPN services using a standards-based IP core. This allows you to provision the VPN services without using LSP or a Label Distribution Protocol (LDP). The system uses IPv4-based mGRE tunnels to encapsulate VPN-labeled IPv4 and IPv6 packets between PEs.
The MPLS VPN over mGRE feature also allows you to deploy existing MPLS VPN LSP-encapsulated technology concurrently with MPLS VPN over mGRE and enables the system to determine which encapsulation method is used to route specific traffic. The ingress PE router determines which encapsulation technology to use when a packet is sent to the remote PE router.
This section includes information on the following topics on MPLS VPN over mGRE feature:
By default, VPN traffic is sent using an LSP. The MPLS VPN over mGRE feature uses user-defined route maps to determine which VPN prefixes are reachable over an mGRE tunnel and which VPN prefixes are reachable using an LSP. The route map is applied to advertisements for VPNv4 and VPNv6 address families. The route map uses a next hop tunnel table to determine the encapsulation method for the VPN traffic.
To route traffic over the mGRE tunnel, the system creates an alternative address space that shows that all next hops are reached by encapsulating the traffic in an mGRE tunnel. To configure a specific route to use an mGRE tunnel, the user adds an entry for that route to the route map. The new entry remaps the Network Layer Reachability Information (NLRI) of the route to the alternative address space. If there is no remap entry in the route map for a route, then traffic on that route is forwarded over an LSP.
When the user configures MPLS VPN over mGRE, the system automatically provisions the alternative address space, normally held in the tunnel-encapsulated virtual routing and forwarding (VRF) instance. To ensure that all traffic reachable through the address space is encapsulated in an mGRE tunnel, the system installs a single default route out of a tunnel. The system also creates a default tunnel on the route map. The user can attach this default route map to the appropriate BGP updates.
Tunnel Endpoint Discovery and Forwarding
In order for the MPLS VPN over mGRE feature to function correctly, the system must be able to discover the remote PEs in the system and construct tunnel forwarding information for these remote PEs. In addition the system must be able to detect when a remote PE is no longer valid and remove the tunnel forwarding information for that PE.
If an ingress PE receives a VPN advertisement over BGP, it uses the route target attributes (which it inserts into the VRF) and the MPLS VPN label from the advertisement, to associate the prefixes with the appropriate customer. The next hop of the inserted route is set to the NLRI of the advertisement.
The advertised prefixes contain information about remote PEs in the system (in the form of NLRIs), and the PE uses this information to notify the system when an NLRI becomes active or inactive. The system uses this notification to update the PE forwarding information.
When the system receives notification of a new remote PE, it adds the information to the tunnel endpoint database, which causes the system to create an adjacency associated with the tunnel interface. The adjacency description includes information on the encapsulation and other processing that the system must perform to send encapsulated packets to the new remote PE.
The adjacency information is placed into the tunnel encapsulated VRF. When a user remaps a VPN NLRI to a route in the VRF (using the route map), the system links the NLRI to the adjacency; therefore the VPN is linked to a tunnel.
When the egress PE receives a packet from a tunnel interface that uses the MPLS VPN over mGRE feature, the PE decapsulates the packet to create a VPN label tagged packet, and sends the packet to the MPLS forwarding (MFI) code.
The MPLS VPN over mGRE feature uses a single tunnel configured as an mGRE tunnel to configure a system with a large number of endpoints (remote PEs). To identify the origin of tunnel-encapsulated packets, the system uses the tunnel source information.
At the transmitting (ingress) PE, when a VPN packet is sent to a tunnel, the tunnel destination is the NLRI. At a receiving (egress) PE, the tunnel source is the address that the packets encapsulated in the mGRE tunnel are received on. Therefore, at the egress PE the packet destination must match the NLRI from the local PE.
If the advertising PE router has an IPv6 address then the NLRI must also be an IPv6 address (regardless of the network between the PEs). If the network between the PEs is IPv4 based, the system creates the IPv6 address of the advertising PE using an IPv4 mapped address in the following form: ::FFFF:IPv4-PE-address. The receiving PE sets the next hop for the VPN tag IPv6 prefixes to the IPv4 address embedded in the IPv6 NLRI. This enables the PE to link VPNv6 traffic to an LSP or an mGRE tunnel in the same way it maps VPNv4 traffic.
When a PE receives VPNv6 updates, it applies the IPv6 route map. The MPLS VPN over mGRE feature uses the IPv6 route map to set the next hop information in the Tunnel_Encap VRF.
How to Configure MPLS VPN over mGRE
To deploy MPLS VPN over mGRE tunnels, you create a VRF instance, enable and configure L3 VPN encapsulation, link the route map to the application template, and set up the BGP VPNv4 and VPNv6 exchange so that updates are filtered through the route map.
The configuration steps to deploy MPLS VPN over mGRE are described in the following sections:
•Configuring an L3VPN Encapsulation Profile (required)
•Configuring BGP and Route Maps (required)
Configuring an L3VPN Encapsulation Profile
This section describes how to configure an L3VPN encapsulation profile.
Note Transport protocols such as IPv6, MPLS, IP, and Layer 2 Tunneling Protocol version 3 (L2TPv3) can also be used in this configuration.
2. configure terminal
3. l3vpn encapsulation ip profile-name
4. transport ipv4 [source interface-type interface-number]
5. protocol gre [key gre-key]
7. show l3vpn encapsulation ip profile-name
Configuring BGP and Route Maps
Perform this task to configure BGP and route maps. The following steps also enable you to link the route map to the application template and set up the BGP VPNv4 and VPNv6 exchange so that the updates are filtered through the route map.
2. configure terminal
3. router bgp as-number
4. bgp log-neighbor-changes
5. neighbor ip-address remote-as as-number
6. neighbor ip-address update-source interface-name interface-number
7. address-family ipv4
8. no synchronization
9. redistribute connected
10. neighbor ip-address activate
11. no auto-summary
13. address-family vpnv4
14. neighbor ip-address activate
15. neighbor ip-address send-community both
16. neighbor ip-address route-map map-name in
18. address-family vpnv6
19. neighbor ip-address activate
20. neighbor ip-address send-community both
21. neighbor ip-address route-map map-name in
23. route-map map-tag permit position
24. set ip next-hop encapsulate l3vpn profile-name
25. set ipv6 next-hop encapsulate l3vpn profile-name
Configuration Examples for MPLS VPN over mGRE
Example: Verifying The MPLS VPN over mGRE Configuration
Use the following examples to verify that the configuration is working properly:
Cisco Express Forwarding (CEF) Switching
You can verify that CEF switching is working as expected:Router# show ip cef vrf Customer_A tunnel 0126.96.36.199/24nexthop 188.8.131.52 Tunnel0 label 16
You can verify the tunnel endpoint that has been created:Router# show tunnel endpoints tunnel 0Tunnel0 running in multi-GRE/IP modeEndpoint transport 184.108.40.206 Refcount 3 Base 0x2AE93F0 Create Time 00:00:42overlay 220.127.116.11 Refcount 2 Parent 0x2AE93F0 Create Time 00:00:42
You can verify that the corresponding adjacency has been created:Router# show adjacency tunnel 0Protocol Interface AddressIP Tunnel0 18.104.22.168(4)TAG Tunnel0 22.214.171.124(3)
You can use show l3vpn encapsulation profile-name command to get information on the basic state of the application. The output of this command provides you details on the references to the underlying tunnel.Router# show l3vpn encapsulation ip tunnel encapProfile: tunnel encaptransport ipv4 source Auto: Loopback0protocol greTunnel Tunnel0 Created [OK]Tunnel Linestate [OK]Tunnel Transport Source (Auto) Loopback0 [OK]
Example: Configuration Sequence For MPLS VPN over mGRE
This example shows the configuration sequence for MPLS VPN over mGRE:vrf definition Customer Ard 100:110route-target export 100:1000route-target import 100:1000!address-family ipv4exit-address-family!address-family ipv6exit-address-family!!ip cef!ipv6 unicast-routingipv6 cef!!l3vpn encapsulation ip sample profile nametransport source loopback 0protocol gre key 1234!!interface Loopback0ip address 126.96.36.199 255.255.255.224ip router isis!interface Serial2/0vrf forwarding Customer Aip address 188.8.131.52 255.255.255.224ipv6 address 3FFE:1001::/64 eui-64no fair-queueserial restart-delay 0!router bgp 100bgp log-neighbor-changesneighbor 184.108.40.206 remote-as 100neighbor 220.127.116.11 update-source Loopback0!address-family ipv4no synchronizationredistribute connectedneighbor 18.104.22.168 activateno auto-summaryexit-address-family!address-family vpnv4neighbor 22.214.171.124 activateneighbor 126.96.36.199 send-community bothneighbor 188.8.131.52 route-map SELECT_UPDATE_FOR_L3VPN inexit-address-family!address-family vpnv6neighbor 184.108.40.206 activateneighbor 220.127.116.11 send-community bothneighbor 18.104.22.168 route-map SELECT_UPDATE_FOR_L3VPN inexit-address-family!address-family ipv4 vrf Customer Ano synchronizationredistribute connectedexit-address-family!address-family ipv6 vrf Customer Aredistribute connectedno synchronizationexit-address-family!!route-map SELECT_UPDATE_FOR_L3VPN permit 10set ip next-hop encapsulate sample profile nameset ipv6 next-hop encapsulate sample profile name
Related Topic Document Title
Configuring MPLS Layer 3 VPNs
Dynamic Layer 3 VPNs with multipoint GRE tunnels
Cisco Express Forwarding
Generic routing encapsulation
MIB MIBs Link
To locate and download MIBs for selected platforms, Cisco software releases, and feature sets, use Cisco MIB Locator found at the following URL:
Generic Routing Encapsulation (GRE)
Key Sequence Number Extensions to GRE
Encapsulating MPLS in IP or Generic Routing Encapsulation
BGP/MPLS IP Virtual Private Networks (VPNs)
Feature Information for MPLS VPN over mGRE
Table 1 lists the release history for this feature.
Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which Cisco software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
Note Table 1 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.
Cisco and the Cisco Logo are trademarks of Cisco Systems, Inc. and/or its affiliates in the U.S. and other countries. A listing of Cisco's trademarks can be found at www.cisco.com/go/trademarks. Third party trademarks mentioned are the property of their respective owners. The use of the word partner does not imply a partnership relationship between Cisco and any other company. (1005R)
Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental.
© 2009-2011 Cisco Systems, Inc. All rights reserved.