Implementing IPv6 VPN Provider Edge Transport over MPLS

IPv6 Provider Edge or IPv6 VPN Provider Edge (6PE/VPE) uses the existing MPLS IPv4 core infrastructure for IPv6 transport. 6PE/VPE enables IPv6 sites to communicate with each other over an MPLS IPv4 core network using MPLS label switched paths (LSPs).

This feature relies heavily on multiprotocol Border Gateway Protocol (BGP) extensions in the IPv4 network configuration on the provider edge (PE) router to exchange IPv6 reachability information (in addition to an MPLS label) for each IPv6 address prefix. Edge routers are configured as dual-stack, running both IPv4 and IPv6, and use the IPv4 mapped IPv6 address for IPv6 prefix reachability exchange.

Familiarity with MPLS and BGP4 configuration and troubleshooting is required for implementing 6PE/VPE.

Overview of 6PE/VPE

Multiple techniques are available to integrate IPv6 services over service provider core backbones:

  • Dedicated IPv6 network running over various data link layers

  • Dual-stack IPv4-IPv6 backbone

  • Existing MPLS backbone leverage

These solutions are deployed on service providers’ backbones when the amount of IPv6 traffic and the revenue generated are in line with the necessary investments and the agreed-upon risks. Conditions are favorable for the introduction of native IPv6 services, from the edge, in a scalable way, without any IPv6 addressing restrictions and without putting a well-controlled IPv4 backbone in jeopardy. Backbone stability is essential for service providers that have recently stabilized their IPv4 infrastructure.

Service providers running an MPLS/IPv4 infrastructure follow similar trends because several integration scenarios that offer IPv6 services on an MPLS network are possible. Cisco Systems has specially developed Cisco 6PE or IPv6 Provider Edge Router over MPLS, to meet all those requirements.

Inter-AS support for 6PE requires support of Border Gateway Protocol (BGP) to enable the address families and to allocate and distribute PE and ASBR labels.


Note

Cisco IOS XR displays actual IPv4 next-hop addresses for IPv6 labeled-unicast and VPNv6 prefixes. IPv4-mapped-to-IPv6 format is not supported.

Benefits of 6PE/VPE

Service providers who currently deploy MPLS experience these benefits of Cisco 6PE/VPE:

  • Minimal operational cost and risk—No impact on existing IPv4 and MPLS services.

  • Provider edge routers upgrade only—A 6PE/VPE router can be an existing PE router or a new one dedicated to IPv6 traffic.

  • No impact on IPv6 customer edge routers—The ISP can connect to any customer CE running Static, IGP or EGP.

  • Production services ready—An ISP can delegate IPv6 prefixes.

  • IPv6 introduction into an existing MPLS service—6PE/VPE routers can be added at any time

Deploying IPv6 over MPLS Backbones

Backbones enabled by 6PE (IPv6 over MPLS) allow IPv6 domains to communicate with each other over an MPLS IPv4 core network. This implementation requires no backbone infrastructure upgrades and no reconfiguration of core routers, because forwarding is based on labels rather than on the IP header itself. This provides a very cost-effective strategy for IPv6 deployment.

IPv6 on the Provider Edge and Customer Edge Routers

Service Provider Edge Routers

6PE is particularly applicable to service providers who currently run an MPLS network. One of its advantages is that there is no need to upgrade the hardware, software, or configuration of the core network, and it eliminates the impact on the operations and the revenues generated by the existing IPv4 traffic. MPLS is used by many service providers to deliver services to customers. MPLS as a multiservice infrastructure technology is able to provide layer 3 VPN, QoS, traffic engineering, fast re-routing and integration of ATM and IP switching.

Customer Edge Routers

Using tunnels on the CE routers is the simplest way to deploy IPv6 over MPLS networks. It has no impact on the operation or infrastructure of MPLS and requires no changes to the P routers in the core or to the PE routers. However, tunnel meshing is required as the number of CEs to connect increases, and it is difficult to delegate a global IPv6 prefix for an ISP.

The following figure illustrates the network architecture using tunnels on the CE routers.

Figure 1. IPv6 Using Tunnels on the CE Routers


IPv6 Provider Edge Multipath

Internal and external BGP multipath for IPv6 allows the IPv6 router to balance load between several paths (for example, the same neighboring autonomous system (AS) or sub-AS, or the same metrics) to reach its destination. The 6PE multipath feature uses multiprotocol internal BGP (MP-IBGP) to distribute IPv6 routes over the MPLS IPv4 core network and to attach an MPLS label to each route.

When MP-IBGP multipath is enabled on the 6PE router, all labeled paths are installed in the forwarding table with available MPLS information (label stack). This functionality enables 6PE to perform load balancing.

OSPFv3 (CE to PE)

The Open Shortest Path First version 3 (OSPFv3) IPv6 VPN Provider Edge (6VPE) feature adds VPN routing and forwarding (VRF) and provider edge-to-customer edge(PE-CE) routing support to Cisco IOS XR OSPFv3 implementation. This feature allows:

  • Multiple VRF support per OSPFv3 routing process

  • OSPFV3 PE-CE extensions

Multiple VRF Support

OSPFv3 supports multiple VRFs in a single routing process that allows scaling to tens and hundreds of VRFs without consuming too much route processor (RP) resources. Multiple OSPFv3 processes can be configured on a single router. In large-scale VRF deployments, this allows partition VRF processing across multiple RPs. It is also used to isolate default routing table or high impact VRFs from the regular VRFs. It is recommended to use a single process for all the VRFs. If needed, a second OSPFv3 process must be configured for IPv6 routing.


Note

A maximum of four OSPFv3 processes are supported.

OSPFv3 PE-CE Extensions

IPv6 protocol is being vastly deployed in today's customer networks. Service Providers (SPs) need to be able to offer Virtual Private Network (VPN) services to their customers for supporting IPv6 protocol, in addition to the already offered VPN services for IPv4 protocol.

In order to support IPv6, routing protocols require additional extensions for operating in the VPN environment. Extensions to OSPFv3 are required in order for OSPFv3 to operate at the PE-CE links.

Restrictions for 6VPE

The restrictions applicable for configuring 6VPE are as follows:

  • When paths of different technologies are resolved over ECMP, it results in heterogeneous ECMP, leading to severe network traffic issues. Don’t use ECMP for any combination of the following technologies:

    • LDP.

    • BGP-LU, including services over BGP-LU loopback peering or recursive services at Level-3.

    • VPNv4.

    • 6PE and 6VPE.

    • EVPN.

    • Recursive static routing.

Configuring 6PE/VPE

Configuration Example

This example shows how to configure 6PE on PE routers to transport the IPv6 prefixes across the IPv4 cloud. Ensure that you configure 6PE on PE routers participating in both the IPv4 cloud and IPv6 clouds. Pointers:

  • For 6PE, you can use all routing protocols supported on Cisco IOS XR software such as BGP, OSPF, IS-IS, and Static to learn routes from both clouds. However, for 6VPE, you can use only the BGP, and Static routing protocols to learn routes. Also, 6VPE supports OSPFv3 routing protocol between PE and CE routers.

    The default allocation mode is per-prefix. While configuring 6PE/VPE on the router, to achieve the required scale value, use per-vrf or per-ce for all routers including peer routers.

  • Route policies must be configured prior to configuring 6PE/VPE.

  • BGP uses the per-vrf label mode for transporting local and redistributed IP prefixes. Before IOS XR Release 7.5.3, BGP assigned a random label for the prefixes. Starting from Release 7.5.3, BGP assigns a label value of 2, the IPv6 Explicit NULL Label, for the same prefixes. 

Router#configure
Router(config)#router bgp 10
Router(config-bgp)#bgp router-id 11.11.11.11
Router(config-bgp)#graceful-restart
Router(config-bgp)#log neighbor changes detail
Router(config-bgp)#address-family ipv6 unicast
Router(config-bgp-af)#label mode per-vrf
Router(config-bgp-af)#redistribute connected
Router(config-bgp-af)#redistribute ospfv3 7
Router(config-bgp-af)#allocate-label all
Router(config-bgp-af)#commit
Router(config-bgp)#neighbor 66:1:2::2
Router(config-bgp-nbr)#remote-as 102
Router(config-bgp-nbr)#address-family ipv6 unicast
Router(config-bgp-nbr-af)#route-policy pass-all in
Router(config-bgp-nbr-af)#route-policy pass-all out
Router(config-bgp-nbr-af)#commit
Router(config-bgp)#neighbor 13.13.13.13
Router(config-bgp-nbr)#remote-as 10
Router(config-bgp-nbr)#update-source Loopback0
Router(config-bgp-nbr)#address-family vpnv4 unicast
Router(config-bgp-nbr-af)#address-family ipv6 labeled-unicast
Router(config-bgp-nbr-af)#address-family vpnv6 unicast
Router(config-bgp-nbr-af)#commit
Router(config-bgp-nbr-af)#exit
Router(config-bgp-nbr)#exit
Router(config-bgp)#vrf red
Router(config-bgp-vrf)#rd 500:1
Router(config-bgp-vrf)#address-family ipv4 unicast
Router(config-bgp-vrf-af)#redistribute connected
Router(config-bgp-vrf-af)#redistribute static
Router(config-bgp-vrf-af)#exit
Router(config-bgp-vrf)#address-family ipv6 unicast
Router(config-bgp-vrf-af)#redistribute connected
Router(config-bgp-vrf-af)#redistribute static
Router(config-bgp-vrf-af)#commit
Router(config-bgp-vrf-af)#!
!
Router(config)#interface HundredGigE0/9/0/0
Router(config-if)#vrf red
Router(config-if)#ipv6 address 4002:110::1/128
Router(config-if)#exit
Router(config)#vrf red
Router(config-vrf)#address-family ipv4 unicast
Router(config-vrf-af)#label mode per-vrf
Router(config-vrf-af)#import route-target
Router(config-vrf-import-rt)#500:1
Router(config-vrf-import-rt)#!
Router(config-vrf-import-rt)#export route-target
Router(config-vrf-export-rt)#500:1
Router(config-vrf-export-rt)#!
Router(config-vrf-export-rt)#!
Router(config-vrf-export-rt)#address-family ipv6 unicast
Router(config-vrf-af)#label mode per-vrf
Router(config-vrf-af)#import route-target
Router(config-vrf-import-rt)#500:1
Router(config-vrf-import-rt)#!
Router(config-vrf-import-rt)#export route-target
Router(config-vrf-export-rt)#500:1
Router(config-vrf-export-rt)#commit

Running Configuration 



router bgp 10
bgp router-id 11.11.11.11
bgp graceful-restart
bgp log neighbor changes detail
!
 address-family ipv6 unicast
  label mode per-vrf
  !
  redistribute connected
  redistribute ospfv3 7
  allocate-label all
!
!
neighbor 66:1:2::2
  remote-as 201
  address-family ipv6 unicast
   route-policy pass-all in
   route-policy pass-all out
  !
!
neighbor 13.13.13.13
  remote-as 10
  update-source Loopback0
  address-family vpnv4 unicast
  !
  address-family ipv6 labeled-unicast
  !
  address-family vpnv6 unicast
!
vrf red
  rd 500:1
  address-family ipv4 unicast
   label mode per-vrf
   !
   redistribute connected
   redistribute static
  !
  address-family ipv6 unicast
   label mode per-vrf
   !
   redistribute connected
   redistribute static
  !
 !
!
interface HundredGigE0/9/0/0
vrf red
Ipv6 address 4002:110::1/128
!
exit
vrf red
address-family ipv4 unicast
import route-target
500:1
!
export route-target
500:1
!
!
address-family ipv6 unicast
import route-target
500:1
!
export route-target
500:1
!

Verification

Router# show route ipv6
Codes: C - connected, S - static, R - RIP, B - BGP, (>) - Diversion path
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
       i - ISIS, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, su - IS-IS summary null, * - candidate default
       U - per-user static route, o - ODR, L - local, G  - DAGR, l - LISP
       A - access/subscriber, a - Application route
       M - mobile route, r - RPL, (!) - FRR Backup path
Gateway of last resort is not set

L    ::ffff:127.0.0.0/104
      [0/0] via ::, 02:10:49
C    66:1:2::/64 is directly connected,
      02:09:39, TenGigE0/0/0/0.2
L    66:1:2::1/128 is directly connected,
      02:09:39, TenGigE0/0/0/0.2
C   66:1:3::/64isdirectlyconnected,  
[20/0] via fe80::200:2cff:fe64:99e2, 02:07:38, TenGigE0/0/0/0.2
B    2000:0:0:1c::/64
      [20/0] via fe80::200:2cff:fe64:99e2, 02:07:38, TenGigE0/0/0/0.2
B    2000:0:0:1d::/64
Local PE :
Router# show bgp ipv6 labeled-unicast 2000:0:0:1c::/64
BGP routing table entry for 2000:0:0:1c::/64
Versions:
  Process           bRIB/RIB  SendTblVer
  Speaker               5033        5033
    Local Label: 66313
Paths: (1 available, best #1)
  Advertised to update-groups (with more than one peer):
    0.1
  Advertised to peers (in unique update groups):
    13.13.13.13
  Path #1: Received by speaker 0
  Advertised to update-groups (with more than one peer):
    0.1
  Advertised to peers (in unique update groups):
    13.13.13.13
  201
    66:1:2::2 from 66:1:2::2 (39.229.0.1)
      Origin IGP, localpref 100, valid, external, best, group-best
      Received Path ID 0, Local Path ID 0, version 5033
      Origin-AS validity: not-found

Remote PE
Router# show bgp ipv6 labeled-unicast 2000:0:0:1c::/64
BGP routing table entry for 2000:0:0:1c::/64
Versions:
  Process           bRIB/RIB  SendTblVer
  Speaker             139679      139679
Paths: (1 available, best #1)
  Advertised to update-groups (with more than one peer):
    0.2
  Path #1: Received by speaker 0
  Advertised to update-groups (with more than one peer):
    0.2
  201
    11.11.11.11 (metric 5) from 13.13.13.13 (11.11.11.11)
      Received Label 66313
      Origin IGP, localpref 100, valid, internal, best, group-best, labeled-unicast
      Received Path ID 0, Local Path ID 0, version 139679
      Originator: 11.11.11.11, Cluster list: 5.5.5.5

Configuring OSPFv3 as the Routing Protocol Between the PE and CE Routers

Configuration Example

This example shows how to configure provider edge (PE)-to-customer edge (CE) routing sessions that use Open Shortest Path First version 3 (OSPFv3). 

Router#config
Router(config)#router ospfv3 7
Router(config-ospfv3)#router-id 10.200.1.7
Router(config-ospfv3)#vrf vrf1
Router(config-ospfv3-vrf)#area 7
Router(config-ospfv3-vrf-ar)#interface Loopback7
Router(config-ospfv3-vrf-ar-if)#!
Router(config-ospfv3-vrf-ar-if)#interface TenGigE0/0/0/3.7
Router(config-ospfv3-vrf-ar-if)#

Running Configuration 


router ospfv3 7
router-id 10.200.1.7
vrf vrf1
  area 7
   interface Loopback7
   !
   interface TenGigE0/0/0/3.7
   !
  !
!

Verification

Router#show ospfv3 7 vrf vrf1 neighbor 
# Indicates Neighbor awaiting BFD session up

Neighbors for OSPFv3 7, VRF vrf1

Neighbor ID     Pri   State           Dead Time   Interface ID    Interface
10.201.7.1      0     FULL/DROTHER    00:00:36    0               TenGigE0/0/0/3.7
    Neighbor is up for 1w0d

Total neighbor count: 1