MPLS L3VPN Configuration Guide [Step by Step]

Topology (GNS3 Lab):

We will pass through the Configuration of MPLS and L3VPN service step by step, this Topology was created with GNS3.




Step 1: Enable MPLS on P & PE

First, we need to enable MPLS on Provider EDGE and Core routers:

On (P) and (PE) routers, we will enable MPLS by entering the command “mpls ip” under all the interfaces which are part of the MPLS backbone.

In our case, we should activate MPLS under the interfaces below:

  • for PE-1: “FastEthernet0/1”
  • for P1: “FastEthernet0/0” and “FastEthernet0/1”
  • for P2: “FastEthernet0/0” and “FastEthernet0/1”
  • for PE-2: “FastEthernet0/0”



* Configuration:

On Router P1:

P1(config)# interface FastEthernet0/0
P1(config-if)# mpls ip
P1(config-if)# interface FastEthernet0/1
P1(config-if)# mpls ip


On Router PE-1:

PE-1(config)# interface FastEthernet0/1
PE-1(config-if)# mpls ip


On Router P-2:

P2(config)# interface FastEthernet0/0
P2(config-if)# mpls ip
P2(config-if)# interface FastEthernet0/1
P2(config-if)# mpls ip


On Router PE-2:

PE-1(config)# interface FastEthernet0/0
PE-1(config-if)# mpls ip



An Alternative way to Enable LDP and MPLS is by using the OSPF LDP autoconfig feature:

PE-1(config)#router ospf 10
PE-1(config-router)#mpls ldp autoconfig area 0


* Verification:

We can verify using the command: “show mpls interfaces” or “show mpls ldp neighbor“:

PE-1#show mpls interfaces
Interface              IP            Tunnel   BGP Static Operational
FastEthernet0/1        Yes (ldp)     No       No  No     Yes


P1#show mpls ldp neighbor
    Peer LDP Ident: 10.10.10.2:0; Local LDP Ident 10.10.10.1:0
        TCP connection: 10.10.10.2.49750 - 10.10.10.1.646
        State: Oper; Msgs sent/rcvd: 41/41; Downstream
        Up time: 00:28:01
        LDP discovery sources:
          FastEthernet0/1, Src IP addr: 1.1.2.2
        Addresses bound to peer LDP Ident:
          1.1.2.2         10.10.10.2      1.1.3.1
    Peer LDP Ident: 10.10.13.1:0; Local LDP Ident 10.10.10.1:0
        TCP connection: 10.10.13.1.20438 - 10.10.10.1.646
        State: Oper; Msgs sent/rcvd: 42/50; Downstream
        Up time: 00:27:50
        LDP discovery sources:
          FastEthernet0/0, Src IP addr: 1.1.1.2
        Addresses bound to peer LDP Ident:
          1.1.1.2         10.10.13.1


Step 2: Basic IP assigment and Intra-BB OSPF routing configuration

First of all, we will configure the interfaces of P and PE with the basic IP assignment:

PE-1 router:

interface Loopback1
 ip address 10.10.13.1 255.255.255.255
!
interface FastEthernet0/1
 ip address 1.1.1.2 255.255.255.252
 mpls ip
 speed auto
 duplex auto

!
router ospf 100
 router-id 10.10.13.1
 network 1.1.1.0 0.0.0.3 area 0
 network 10.10.13.1 0.0.0.0 area 0


P-1 router:

interface Loopback1
 ip address 10.10.10.1 255.255.255.255
!
interface FastEthernet0/0
 ip address 1.1.1.1 255.255.255.252
 speed auto
 duplex auto
 mpls ip
!
interface FastEthernet0/1
 ip address 1.1.2.1 255.255.255.252
 speed auto
 duplex auto
 mpls ip

!
router ospf 100
 router-id 10.10.10.1
 network 1.1.1.0 0.0.0.3 area 0
 network 1.1.2.0 0.0.0.3 area 0
 network 10.10.10.1 0.0.0.0 area 0


P-2 router:

interface Loopback1
 ip address 10.10.10.2 255.255.255.255
!
interface FastEthernet0/0
 ip address 1.1.2.2 255.255.255.252
 speed auto
 duplex auto
 mpls ip
!
interface FastEthernet0/1
 ip address 1.1.3.1 255.255.255.252
 speed auto
 duplex auto
 mpls ip
!

router ospf 100
 router-id 10.10.10.2
 network 1.1.2.0 0.0.0.3 area 0
 network 1.1.3.0 0.0.0.3 area 0
 network 10.10.10.2 0.0.0.0 area 0


PE-2 router:

interface Loopback1
 ip address 10.10.14.1 255.255.255.255
!
interface FastEthernet0/0
 ip address 1.1.3.2 255.255.255.252
 speed auto
 duplex auto
 mpls ip
!
router ospf 100
 router-id 10.10.14.1
 network 1.1.3.0 0.0.0.3 area 0
 network 10.10.14.1 0.0.0.0 area 0


Step 3: Configure MP-BGP on PE Routers

MP-BGP is configured only on the PE routers: P routers rely entirely on the provider IGP and MPLS to forward traffic through the provider network, and CE routers have no knowledge of routes outside their own VRF.

On PE-1 router:

router bgp 65000
 bgp log-neighbor-changes
 neighbor 10.10.14.1 remote-as 65000
 neighbor 10.10.14.1 update-source Loopback1
 !
 address-family vpnv4
  neighbor 10.10.14.1 activate
  neighbor 10.10.14.1 send-community extended
 exit-address-family


On PE-2 router:

router bgp 65000
 bgp log-neighbor-changes
 neighbor 10.10.13.1 remote-as 65000
 neighbor 10.10.13.1 update-source Loopback1
 !
 address-family vpnv4
  neighbor 10.10.13.1 activate
  neighbor 10.10.13.1 send-community extended
 exit-address-family



Step 4: Configure VRF per Customer on PE routers

on PE-1:

ip vrf Customer_A
 rd 65000:1
 route-target export 65000:1
 route-target import 65000:1
!
ip vrf Customer_B
 rd 65000:2
 route-target export 65000:2
 route-target import 65000:2


on PE-2:

ip vrf Customer_A
 rd 65000:1
 route-target export 65000:1
 route-target import 65000:1
!
ip vrf Customer_B
 rd 65000:2
 route-target export 65000:2
 route-target import 65000:2

Step 5: Configure OSPF adjacency between CE-PE

Customer A:

On PE-1:

interface FastEthernet0/0
 ip vrf forwarding Customer_A
 ip address 1.1.3.1 255.255.255.252
 ip ospf 2 area 0
 speed auto
 duplex auto

!
router ospf 2 vrf Customer_A
 router-id 1.1.3.1
 redistribute bgp 65000 subnets


On PE-2:

interface FastEthernet0/1
 ip vrf forwarding Customer_A
 ip address 1.1.6.1 255.255.255.252
 ip ospf 2 area 0
 speed auto
 duplex half
!
router ospf 2 vrf Customer_A
 router-id 1.1.6.1
 redistribute bgp 65000 subnets

Customer B:

On PE-1:

interface FastEthernet1/0
 ip vrf forwarding Customer_B
 ip address 2.2.3.1 255.255.255.252
 ip ospf 3 area 0
 duplex full

!
router ospf 3 vrf Customer_B
 router-id 2.2.3.1
 redistribute bgp 65000 subnets


On PE-2:

interface FastEthernet1/0
 ip vrf forwarding Customer_B
 ip address 2.2.6.1 255.255.255.252
 ip ospf 3 area 0
 duplex full
!
router ospf 3 vrf Customer_B
 router-id 2.2.6.1
 redistribute bgp 65000 subnets



Step 6: Route Redistribution

On PE-1:

router ospf 2 vrf Customer_A
 router-id 1.1.3.1
 redistribute bgp 65000 subnets

router ospf 3 vrf Customer_B
 router-id 2.2.3.1
 redistribute bgp 65000 subnets

!!

router bgp 65000
 address-family ipv4 vrf Customer_A
  redistribute ospf 2
 exit-address-family
 !
 address-family ipv4 vrf Customer_B
  redistribute ospf 3
 exit-address-family



On PE-2:

router ospf 2 vrf Customer_A
 router-id 1.1.6.1
 redistribute bgp 65000 subnets

router ospf 3 vrf Customer_B
 router-id 2.2.6.1
 redistribute bgp 65000 subnets

!!

router bgp 65000
 address-family ipv4 vrf Customer_A
  redistribute ospf 2
 exit-address-family
 !
 address-family ipv4 vrf Customer_B
  redistribute ospf 3
 exit-address-family

Verification:

  • MPLS forwarding Table:

PE-1:


PE-1#show mpls forwarding-table
Local      Outgoing   Prefix           Bytes Label   Outgoing   Next Hop
Label      Label      or Tunnel Id     Switched      interface
16         16         10.10.10.2/32    0             Fa0/1      1.1.1.1
17         Pop Label  10.10.10.1/32    0             Fa0/1      1.1.1.1
18         17         1.1.3.0/30       0             Fa0/1      1.1.1.1
19         Pop Label  1.1.2.0/30       0             Fa0/1      1.1.1.1
20         18         10.10.14.1/32    0             Fa0/1      1.1.1.1
21         No Label   1.1.3.0/30[V]    0             aggregate/Customer_A
22         No Label   10.10.11.1/32[V] 2173386       Fa0/0      1.1.3.2
23         No Label   2.2.3.0/30[V]    2442          aggregate/Customer_B
24         No Label   10.20.11.1/32[V] 0             Fa1/0      2.2.3.2
PE-1#

PE-2:


PE-2#show mpls forwarding-table
Local      Outgoing   Prefix           Bytes Label   Outgoing   Next Hop
Label      Label      or Tunnel Id     Switched      interface
16         19         10.10.13.1/32    0             Fa0/0      1.1.3.1
17         Pop Label  10.10.10.2/32    0             Fa0/0      1.1.3.1
18         16         10.10.10.1/32    0             Fa0/0      1.1.3.1
19         17         1.1.1.0/30       0             Fa0/0      1.1.3.1
20         Pop Label  1.1.2.0/30       0             Fa0/0      1.1.3.1
21         No Label   1.1.6.0/30[V]    0             aggregate/Customer_A
22         No Label   10.10.12.1/32[V] 1018150       Fa0/1      1.1.6.2
23         No Label   2.2.6.0/30[V]    0             aggregate/Customer_B
24         No Label   10.20.22.1/32[V] 1812          Fa1/0      2.2.6.2

Bilel-A

Enthusiastic Network Engineer specializing in Cisco ACI, passionate about solving challenges. A lifelong learner who loves gaining and sharing knowledge. Profile: https://www.linkedin.com/in/bilel-ameur-71116b2b5

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