Creating MPLS Layer 3 VPN

When used with MPLS, the VPN feature allows several sites to interconnect transparently through a service provider's network. One service provider network can support several different IP VPNs. Each of these appears to its users as a private network, separate from all other networks. Within a VPN, each site can send IP packets to any other site in the same VPN.

Each VPN is associated with one or more VPN routing and forwarding instances (VRFs). A VRF consists of an IP routing table, a derived Cisco express forwarding (CEF) table, and a set of interfaces that use this forwarding table.

The router maintains a separate routing and CEF table for each VRF. This prevents information being sent outside the VPN and allows the same subnet to be used in several VPNs without causing duplicate IP address problems.

In this document, we'll be configuring basic MPLS Layer 3 VPN for two customers, each having two physical sites at different location.

Network Topology:

Creating MPLS Layer 3 VPN
MPLS Layer 3 VPN
Download the gns3 topology here:

Creating MPLS Layer 3 VPN.7z



In the Network diagram,
  • P1 and P2 are provider's core routers.
  • PE1 and PE2 are provider's edge routers that connect to customer sites.
  • CE1_A and CE2_A are customer edge routers of Customer-A at physically different locations.
  • CE1_B and CE2_B are customer edge routers of Customer-B at physically different locations.
  • Both the customers, Customer-A and Customer-B have different ASN at each location.

Configuration


P1
In the configuration, interfaces facing the core of the provider network are in OSPF area 0 and interfaces connected to the edge routers are in OSPF area 10. Also we have forcefully configured to use IP address of Loopback0 as mpls ldp router-id i.e. router ID of mpls ldp process will change immediately after executing the command, without waiting to restart the device.
hostname P1
!
ip cef
!
interface Loopback0
 ip address 192.0.2.1 255.255.255.255
 ip ospf 1 area 0.0.0.0
!
interface GigabitEthernet0/0
 description ## Connected to PE1 G-0/0 ##
 ip address 198.51.100.1 255.255.255.252
 ip ospf 1 area 0.0.0.10
 media-type gbic
 speed 1000
 duplex full
 negotiation auto
 mpls ip
!
interface GigabitEthernet1/0
 description ## Connected to P2 G-1/0 ##
 ip address 198.51.100.5 255.255.255.252
 ip ospf 1 area 0.0.0.0
 negotiation auto
 mpls ip
!
router ospf 1
!
mpls ldp router-id Loopback0 force

P2
In the configuration, interfaces facing the core of the provider network are in OSPF area 0 and interfaces connected to the edge routers are in OSPF area 10. Also we have forcefully configured to use IP address of Loopback0 as mpls ldp router-id i.e. router ID of mpls ldp process will change immediately after executing the command, without waiting to restart the device.
hostname P2
!
ip cef
!
interface Loopback0
 ip address 192.0.2.2 255.255.255.255
 ip ospf 1 area 0.0.0.0
!
interface GigabitEthernet0/0
 description ## Connected to PE2 G-0/0 ##
 ip address 198.51.100.9 255.255.255.252
 ip ospf 1 area 0.0.0.10
 media-type gbic
 speed 1000
 duplex full
 negotiation auto
 mpls ip
!
interface GigabitEthernet1/0
 description ## Connected to P1 G-0/0 ##
 ip address 198.51.100.6 255.255.255.252
 ip ospf 1 area 0.0.0.0
 negotiation auto
 mpls ip
!
router ospf 1
!
mpls ldp router-id Loopback0 force

PE1
Both the customers, Customer-A and Customer-B are using different ASN at each location for simplicity of configuration. We can also use same autonomous system number for a customer at all the his locations, but for that we have to use allowas-in feature on CE device. In the configuration, the device is configured with different VRFs for both the customers with route distinguisher in the form of . Both the values i.e. import and export route targets are used as same for simplicity. VRF configuration needs to done on PE routers only and not on P routers. Appropriate interface is assigned to each VRF. Three BGP neighbors have been configured, one BGP neighborship with Customer-A connected to PE1, second BGP neighborship with Customer-B connected to PE1 and third iBGP neighborship with PE2 which is the provider's edge router at physically different location, to which other site of Customer-A and Customer-B is connected, to create a VPN through Provider's core network.
hostname PE1
!
ip vrf Customer-A
 rd 64500:110
 route-target export 64500:1000
 route-target import 64500:1000
!
ip vrf Customer-B
 rd 64500:120
 route-target export 64500:2000
 route-target import 64500:2000
!
ip cef
!
interface Loopback0
 ip address 192.0.2.3 255.255.255.255
 ip ospf 1 area 0.0.0.10
!
interface GigabitEthernet0/0
 description ## Connected to P1 G-1/0 ##
 ip address 198.51.100.2 255.255.255.252
 ip ospf 1 area 0.0.0.10
 media-type gbic
 speed 1000
 duplex full
 negotiation auto
 mpls ip
!
interface GigabitEthernet1/0
 description ## Connected to CE1_A ##
 ip vrf forwarding Customer-A
 ip address 10.0.0.1 255.255.255.252
 negotiation auto
!
interface GigabitEthernet2/0
 description ## Connected to CE1_B ##
 ip vrf forwarding Customer-B
 ip address 10.0.0.5 255.255.255.252
 negotiation auto
!
router ospf 1
!
router bgp 64500
 bgp log-neighbor-changes
 neighbor 192.0.2.4 remote-as 64500
 neighbor 192.0.2.4 update-source Loopback0
 !
 address-family vpnv4
  neighbor 192.0.2.4 activate
  neighbor 192.0.2.4 send-community extended
 exit-address-family
 !
 address-family ipv4 vrf Customer-A
  neighbor 10.0.0.2 remote-as 65531
  neighbor 10.0.0.2 activate
 exit-address-family
 !
 address-family ipv4 vrf Customer-B
  neighbor 10.0.0.6 remote-as 64512
  neighbor 10.0.0.6 activate
 exit-address-family
!
mpls ldp router-id Loopback0 force

PE2
In the configuration, the device is configured with different VRFs for both the customers with route distinguisher in the form of . Both the values i.e. import and export route targets are used as same for simplicity. Appropriate interface is assigned to each VRF. Three BGP neighbors have been configured, one BGP neighborship with Customer-A connected to PE2, second BGP neighborship with Customer-B connected to PE2 and third iBGP neighborship with PE1 which is the provider's edge router at physically different location, to which other site of Customer-A and Customer-B is connected, to create a VPN through Provider's core network.
hostname PE2
!
ip vrf Customer-A
 rd 64500:110
 route-target export 64500:1000
 route-target import 64500:1000
!
ip vrf Customer-B
 rd 64500:120
 route-target export 64500:2000
 route-target import 64500:2000
!
ip cef
!
interface Loopback0
 ip address 192.0.2.4 255.255.255.255
 ip ospf 1 area 0.0.0.10
!
interface GigabitEthernet0/0
 description ## Connected to P2 G-0/0 ##
 ip address 198.51.100.10 255.255.255.252
 ip ospf 1 area 0.0.0.10
 media-type gbic
 speed 1000
 duplex full
 negotiation auto
 mpls ip
!
interface GigabitEthernet1/0
 description ## Connected to CE2_A ##
 ip vrf forwarding Customer-A
 ip address 10.1.1.1 255.255.255.252
 negotiation auto
!
interface GigabitEthernet2/0
 description ## Connected to CE2_B ##
 ip vrf forwarding Customer-B
 ip address 10.1.1.5 255.255.255.252
 negotiation auto
!
router ospf 1
!
router bgp 64500
 bgp log-neighbor-changes
 neighbor 192.0.2.3 remote-as 64500
 !
 address-family ipv4
  neighbor 192.0.2.3 activate
  neighbor 192.0.2.4 update-source Loopback0 
exit-address-family
 !
 address-family vpnv4
  neighbor 192.0.2.3 activate
  neighbor 192.0.2.3 send-community extended
 exit-address-family
 !
 address-family ipv4 vrf Customer-A
  neighbor 10.1.1.2 remote-as 65532
  neighbor 10.1.1.2 activate
 exit-address-family
 !
 address-family ipv4 vrf Customer-B
  neighbor 10.1.1.6 remote-as 64513
  neighbor 10.1.1.6 activate
 exit-address-family
!
mpls ldp router-id Loopback0 force


All the customer edge routers are connected to ISP through a point-to-point link and using BGP for advertising their LAN segment. Loopback1 is configured to emulate inside network of customer. A default route is configured on all CE devices pointing towards ISP.

CE1_A
hostname CE1_A
!
interface Loopback1
 ip address 172.16.1.1 255.255.255.0
!
interface GigabitEthernet0/0
 description ## Connected to ISP ##
 ip address 10.0.0.2 255.255.255.252
 media-type gbic
 speed 1000
 duplex full
 negotiation auto
!
router bgp 65531
 bgp log-neighbor-changes
 neighbor 10.0.0.1 remote-as 64500
!
 address-family ipv4
  network 172.16.1.0 mask 255.255.255.0
  neighbor 10.0.0.1 activate
 exit-address-family
!
ip route 0.0.0.0 0.0.0.0 10.0.0.1

CE2_A
hostname CE2_A
!
interface Loopback1
 ip address 172.16.2.1 255.255.255.0
!
interface GigabitEthernet0/0
 description ## Connected to ISP ##
 ip address 10.1.1.2 255.255.255.252
 media-type gbic
 speed 1000
 duplex full
 negotiation auto
!
router bgp 65532
 bgp log-neighbor-changes
 network 172.16.2.0 mask 255.255.255.0
 neighbor 10.1.1.1 remote-as 64500
!
ip route 0.0.0.0 0.0.0.0 10.1.1.1

CE1_B
hostname CE1_B
!
interface Loopback1
 ip address 192.168.1.1 255.255.255.0
!
interface GigabitEthernet0/0
 description ## Connected to ISP ##
 ip address 10.0.0.6 255.255.255.252
 media-type gbic
 speed 1000
 duplex full
 negotiation auto
!
router bgp 64512
 bgp log-neighbor-changes
 network 192.168.1.0
 network 192.168.1.1
 neighbor 10.0.0.5 remote-as 64500
!
ip route 0.0.0.0 0.0.0.0 10.0.0.5

CE2_B
hostname CE2_B
!
interface Loopback1
 ip address 192.168.2.1 255.255.255.0
!
interface GigabitEthernet0/0
 description ## Connected to ISP ##
 ip address 10.1.1.6 255.255.255.252
 media-type gbic
 speed 1000
 duplex full
 negotiation auto
!
router bgp 64513
 bgp log-neighbor-changes
 network 192.168.2.0
 neighbor 10.1.1.5 remote-as 64500
!
ip route 0.0.0.0 0.0.0.0 10.1.1.5




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