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MPLS VPN Basic ConfigurationThis section outlines the generic configurations required on the routers in the service provider domain to implement MPLS VPN. The configurations of the PE and P routers will be covered in this section. The subsequent sections in this chapter delve into each of the configuration blocks on the PE and P routers alone. The configurations required to implement PE-CE routing sessions are discussed in Chapters 4 through 6, depending on the PE-CE protocol in use. All configurations outlined in the following sections are performed in the network shown in Figure 3-11. For simplicity, only connected networks that are part of the VRF will be redistributed into the MP-BGP processes. Figure 3-11. Network Topology: MPLS VPN PE and P Configuration
The topology in Figure 3-11 attempts to implement a simple intranet VPN between two sites belonging to Customer A, site 1 and site 2. The customer network consists of the CE routers CE1-A and CE2-A. In addition, two loopbacks (loopback 1) on PE1-AS1 and PE2-AS1 will be configured as part of the VRF CustomerA and be redistributed into the MP-BGP routing contexts. Configuration of CE RoutersThe configuration of route exchange between PE and CE routers involves the implementation of a routing protocol (or static/default routes) on the CE routers. No specific configuration other than the regular routing protocol configuration is required on the CE routers. On the PE router, VRF routing contexts (or address family contexts) are required for route exchange between the PE and CE. These routes are then mutually redistributed with the MP-BGP process per VRF. Configurations for the above based on protocol choice between PE and CE will be covered in Chapters 4 through 6. Configuring MPLS Forwarding and VRF Definition on PE RoutersConfiguring MPLS forwarding is the first step to provision the service provider's MPLS VPN backbone. This step ensures the service provider's readiness to provide MPLS-related services to prospective customers. At a minimum, the steps to configure MPLS forwarding on PE routers are
These steps have already been discussed in Chapters 1 and 2 and thus have not been shown. In this section, we configure VRFs on the PE routers. Figure 3-12 shows the configuration steps on the PE routers to configure VRF definition. Figure 3-12. VRF Definition on PE Routers: Configuration Steps
Final VRF Configuration on PE1-AS1 RouterExample 3-10 shows the VRF configuration on the PE1-AS1 router. Example 3-10. VRF Configuration of PE1-AS1ip vrf CustomerA rd 1:100 route-target export 1:100 route-target import 1:100 ! interface Serial1/0 description PE-CE link to CE1-A ip vrf forwarding CustomerA ip address 172.16.1.1 255.255.255.0 ! Interface Loopback1 ip vrf forwarding CustomerA ip address 172.16.100.1 255.255.255.255 Verification of VRF Configuration on PE RoutersThe show ip vrf command is used to verify if the correct VRF exists on the interface. Example 3-11 indicates that the correct VRF CustomerA is configured on the Serial1/0 interface on the PE1 router. Example 3-11. show ip vrf on PE1-AS1PE1-AS1#show ip vrf
Name Default RD Interfaces
CustomerA 1:100 Se1/0
Lo1The show ip vrf interfaces command provides the listing of interfaces that are activated for a particular VRF. Example 3-12 shows that Serial1/0 is active for VRF VRF-Static. Example 3-12. show ip vrf interfaces on PE1-AS1PE1-AS1#show ip vrf interfaces
Interface IP-Address VRF Protocol
Serial1/0 172.16.1.1 CustomerA up
Lo1 172.16.100.1 CustomerA upConfiguration of BGP PE-PE Routing on PE RoutersConfiguring BGP PE-PE routing between the PE routers is the next step in an MPLS VPN deployment. The purpose of this step is to ensure that VPNv4 routes can be transported across the service provider backbone using MP-iBGP. The P router is transparent to this entire process and, therefore, does not carry any customer routes. Figure 3-13 illustrates the steps for configuring BGP PE-PE routing sessions between the PE routers. Figure 3-13. BGP PE-PE Routing Configuration Steps
BGP PE-PE Routing Final Configuration on PE1-AS1 and PE2-AS1 RouterExample 3-17 shows the final BGP PE-PE routing configuration on the PE1-AS1 and PE2-AS1 router. Example 3-17. BGP PE-PE Configurations of PE1-AS1 and PE2-AS1 Routers!PE1-AS1 Router: router bgp 1 no synchronization neighbor 10.10.10.102 remote-as 1 no auto-summary ! address-family vpnv4 neighbor 10.10.10.102 activate neighbor 10.10.10.102 send-community extended exit-address-family ! address-family ipv4 vrf CustomerA redistribute connected no auto-summary no synchronization exit-address-family __________________________________________________________________________ !PE2-AS1 Router: router bgp 1 no synchronization bgp log-neighbor-changes neighbor 10.10.10.101 remote-as 1 neighbor 10.10.10.101 update-source Loopback0 no auto-summary ! address-family vpnv4 neighbor 10.10.10.101 activate neighbor 10.10.10.101 send-community extended exit-address-family ! address-family ipv4 vrf CustomerA redistribute connected no auto-summary no synchronization exit-address-family Verification and Monitoring of BGP PE-PE Routing on PE RoutersAfter configuring BGP PE-PE routing between the PE routers, you can verify that the MP-iBGP neighbors are operational by issuing any of the following commands:
Example 3-18 shows that the VPNv4 neighbor relationship is formed. Example 3-18. VPN Neighbor Relationship VerificationPE1#show ip bgp vpnv4 all summary BGP router identifier 10.10.10.101, local AS number 1 BGP table version is 7, main routing table version 7 Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd 10.10.10.102 4 1 202 200 7 0 0 00:00:39 0 __________________________________________________________________________________ PE2#show ip bgp vpnv4 all summary BGP router identifier 10.10.10.102, local AS number 1 BGP table version is 1, main routing table version 1 Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd 10.10.10.101 4 1 11 11 1 0 0 00:07:16 0 Configuration of P RouterNo special configurations need to be performed on the P routers P1-AS1 and P1-AS2 for MPLS VPN support. Because the P routers only participate in MPLS labeled packet forwarding, the only requirements are those of an LSR in an MPLS network, namely, IGP for NLRI exchange and LDP for label assignment and distribution. As always, CEF needs to be enabled on all interfaces configured for MPLS forwarding. Configuration of the P1-AS1 router is shown in Example 3-19. Example 3-19. P1-AS1 Configurationmpls ldp router-id loopback0 ! interface Serial0/0 ip address 10.10.10.2 255.255.255.252 mpls ip ! interface Serial1/0 ip address 10.10.10.5 255.255.255.252 mpls ip ! Interface loopback0 ip address 10.10.10.200 255.255.255.255 ! router ospf 1 network 10.0.0.0 0.255.255.255 area 0 ! Label Verification and Control and Data Plane OperationAfter configuring devices in the network as per the previous steps, the verification of label allocation and propagation can be performed on the PE and P routers using the commands described in Figure 3-14. Figure 3-14. Label Allocation Verification and Control/Data Plane Operation
The control plane and data plane operation for network 172.16.100.1 as part of VRF CustomerA is depicted in Figure 3-14. Note that the outgoing label mapped to prefix 172.16.100.1 on PE1-AS1 is aggregate and not untagged. For all networks that are directly connected to the PE router (like loopbacks or interface IP networks) that are part of a VRF, the outgoing label mapped in the LFIB is the aggregate label. If, however, the incoming VPN packet is to be forwarded to a next-hop address (like that of a connected CE router), the outgoing label mapping is untagged. Thus, aggregate and untagged labels that were explained in Chapter 1 are encountered in MPLS VPN implementations. |
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