MPLS L3VPN Services using Segment Routing
Currently, MPLS Label Distribution Protocol (LDP) is the widely used transport for MPLS L3VPN services.
The user can achieve better resilience and convergence for the network traffic, by transporting MPLS L3VPN
services using Segment Routing (SR), instead of MPLS LDP. Segment routing can be directly applied to the
MPLS architecture without changing the forwarding plane. In a segment-routing network using the MPLS
data plane, LDP or other signaling protocol is not required; instead label distribution is performed by IGP
(IS-IS or OSPF) or BGP protocol. Removing protocols from the network simplifies its operation and makes
it more robust and stable by eliminating the need for protocol interaction. Segment routing utilizes the network
bandwidth more effectively than traditional MPLS networks and offers lower latency.
Configure MPLS L3VPN over Segment Routing
Topology
Given below is a network scenario, where MPLS L3VPN service is transported using Segment Routing.
Figure 10: MPLS L3VPN over Segment Routing
In this topology, CE1 and CE2 are the two customer routers. ISP has two PE routers, PE1 and PE2 and a P
router. RIP is used for the edge protocol support between the CE and PE routers. Label distribution can be
performed by IGP (IS-IS or OSPF) or BGP. OSPF is used in this scenario.
Customer's autonomous system is 65534, which peers with ISP's autonomous system 65000. This must be a
vrf peering to prevent route advertisement into the global IPv4 table. The ISP routers PE1 and PE2 contain
the VRF (for example, vrf1601) for the customer. PE1 and PE2 export and import the same route targets,
although this is not necessary.
Loopback interfaces are used in this topology to simulate the attached networks.
Configuration
You must complete these tasks to ensure the successful configuration of MPLS L3VPN over segment routing:
• Configure Segment Routing in MPLS Core, on page 48
• Configure protocol support on PE-CE (refer, Connect MPLS VPN Customers, on page 15 )
• Configure protocol support on PE-PE (refer, Configure Multiprotocol BGP on the PE Routers and Route
Reflectors, on page 12)
L3VPN Configuration Guide for Cisco NCS 540 Series Routers, IOS XR Release 6.3.x
47
MPLS L3VPN Overview
MPLS L3VPN Services using Segment Routing
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