IPv6 over MPLS backbones enables isolated IPv6 domains to communicate with each other over an MPLS IPv4 core network. This implementation requires only a few backbone infrastructure upgrades and no reconfiguration of core devices because forwarding is based on labels rather than the IP header itself, providing a very cost-effective strategy for the deployment of IPv6.

Additionally, the inherent Virtual Private Network (VPN) and MPLS traffic engineering (MPLS-TE) services available within an MPLS environment allow IPv6 networks to be combined into IPv4 VPNs or extranets over an infrastructure supporting IPv4 VPNs and MPLS-TE.

Using any circuit transport for deploying IPv6 over MPLS networks has no impact on the operation or infrastructure of MPLS, and requires no configuration changes to the core or provider edge devices. Communication between the remote IPv6 domains runs native IPv6 protocols over a dedicated link, where the underlying mechanisms are fully transparent to IPv6. The IPv6 traffic is tunneled using the Any Transport over MPLS (MPLS/AToM) or Ethernet over MPLS (EoMPLS) feature with the devices connected through an ATM OC-3 or Ethernet interface, respectively.

The figure below shows the configuration for IPv6 over any circuit transport over MPLS.

Figure 1. IPv6 over a Circuit Transport over MPLS

Using tunnels on the customer edge (CE) devices is the simplest way of deploying IPv6 over MPLS networks with no impact on the operation or infrastructure of MPLS, and no configuration changes to the core or provider edge devices. Communication between the remote IPv6 domains uses standard tunneling mechanisms and requires the CE devices to be configured to run dual IPv4 and IPv6 protocol stacks. The figure below shows the configuration using tunnels on the CE devices.

Figure 2. IPv6 Using Tunnels on the CE Devices

Refer to Implementing Tunneling for IPv6 for configuration information on manually configured tunnels, automatic tunnels, and 6to4 tunnels.

Limitations on using tunnels involve the manual configuring of a mesh of tunnels on the CE devices, creating scaling issues for large networks.

The Cisco implementation of IPv6 provider edge device over MPLS is called 6PE, and it enables IPv6 sites to communicate with each other over an MPLS IPv4 core network using MPLS label switched paths (LSPs). This feature relies on multiprotocol Border Gateway Protocol (BGP) extensions in the IPv4 network configuration on the provider edge (PE) device to exchange IPv6 reachability information in addition to an MPLS label for each IPv6 address prefix to be advertised. Edge devices are configured to be dual stack running both IPv4 and IPv6, and use the IPv4 mapped IPv6 address for IPv6 prefix reachability exchange.

A hierarchy of labels is imposed on the 6PE ingress device to keep the IPv6 traffic transparent to all the core devices. The top label provides connectivity inside the IPv4 MPLS core network and the label is distributed by Label Distribution Protocol (LDP), Tag Distribution Protocol (TDP), or Resource Reservation Protocol (RSVP). TDP and LDP can both be used for label distribution, but RSVP is used only in the context of MPLS-TE label exchange. The bottom label, automatically assigned to the IPv6 prefix of the destination, is distributed by multiprotocol BGP and used at each 6PE egress device for IPv6 forwarding.

In the figure below the 6PE devices are configured as dual stack devices able to route both IPv4 and IPv6 traffic. Each 6PE device is configured to run LDP, TDP, or RSVP (if traffic engineering is configured) to bind the IPv4 labels. The 6PE devices use multiprotocol BGP to exchange reachability information with the other 6PE devices within the MPLS domain, and to distribute IPv6 labels between them. All 6PE and core devices--P devices in Figure 3--within the MPLS domain share a common IPv4 Interior Gateway Protocol (IGP) such as Open Shortest Path First (OSPF) or Integrated Intermediate System-to-Intermediate System (IS-IS).

Figure 3. 6PE Device Topology

The interfaces on the 6PE devices connecting to the CE device can be configured to forward IPv6 traffic, IPv4 traffic, or both types of traffic depending on the customer requirements. 6PE devices advertise IPv6 reachability information learned from their 6PE peers over the MPLS cloud. Service providers can delegate an IPv6 prefix from their registered IPv6 prefixes over the 6PE infrastructure; otherwise, there is no impact on the CE device.

The P devices in the core of the network are not aware that they are switching IPv6 packets. Core devices are configured to support MPLS and the same IPv4 IGP as the PE devices to establish internal reachability inside the MPLS cloud. Core devices also use LDP, TDP, or RSVP for binding IPv4 labels. Implementing the Cisco 6PE feature does not have any impact on the MPLS core devices.

Within the MPLS network, IPv6 traffic is forwarded using label switching, making the IPv6 traffic transparent to the core of the MPLS network. No IPv6 over IPv4 tunnels or Layer 2 encapsulation methods are required.

To deploy IPv6 over a circuit transport over MPLS, the IPv6 devices must be configured for IPv6 connectivity. The MPLS device configuration requires AToM configuration or EoMPLS configuration.

• Specifying the Source Address Interface on a 6PE Device
• Binding and Advertising the 6PE Label to Advertise Prefixes
• Configuring IBGP Multipath Load Sharing

Specifying the Source Address Interface on a 6PE Device

Two configuration tasks using the network shown in the figure below are required at the 6PE1 device to enable the 6PE feature.

The customer edge device--CE1 in the figure below--is configured to forward its IPv6 traffic to the 6PE1 device. The P1 device in the core of the network is assumed to be running MPLS, a label distribution protocol, an IPv4 IGP, and Cisco Express Forwarding or distributed Cisco Express Forwarding, and does not require any new configuration to enable the 6PE feature.

Figure 4. 6PE Configuration Example

Before You Begin

• The 6PE devices--the 6PE1 and 6PE2 devices in the figure below--must be members of the core IPv4 network. The 6PE device interfaces attached to the core network must be running MPLS, the same label distribution protocol, and the same IPv4 IGP, as in the core network.
• The 6PE devices must also be configured to be dual stack to run both IPv4 and IPv6.

SUMMARY STEPS

1.    enable


2.    configure terminal


3.    ipv6 unicast-routing


4.    ipv6 cef


5.    interface type number


6.    ipv6 address ipv6-address / prefix-length | prefix-name sub-bits / prefix-length

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Device> enable	Enables privileged EXEC mode. Enter your password if prompted.
Step 2	configure terminal Example: Device# configure terminal	Enters global configuration mode.
Step 3	ipv6 unicast-routing Example: Device(config)# ipv6 unicast-routing	Enables the forwarding of IPv6 unicast datagrams.
Step 4	ipv6 cef Example: Device(config)# ipv6 cef	Enables IPv6 Cisco Express Forwarding.
Step 5	interface type number Example: Device(config)# interface Serial 0/0	Specifies an interface type and number and enters interface configuration mode. In the context of this feature, the interface to be configured is the interface communicating with the CE device.
Step 6	ipv6 address ipv6-address / prefix-length | prefix-name sub-bits / prefix-length Example: Device(config-if)# ipv6 address 2001:DB8:FFFF::2/64	Configures an IPv6 address based on an IPv6 general prefix and enable IPv6 processing on an interface.

Device> enable

Device# configure terminal

Device(config)# router bgp 65000

Device(config-router)# no bgp default ipv4-unicast

Device(config-router)# neighbor 192.168.99.70 remote-as 65000

Device(config-router)# neighbor 192.168.99.70 update-source Loopback 0

Device(config-router)# address-family ipv6

Device(config-router-af)# neighbor 192.168.99.70 activate

Device(config-router-af)# neighbor 192.168.99.70 send-label

Device> enable 

Device# configure terminal 

Device(config)# router bgp 65000 

Device(config-router)# maximum-paths ibgp 3