Overview

Multiprotocol Label Switching (MPLS) is a protocol-agnostic routing technique that forwards the data from one node to the next node based on labels rather than network addresses. MPLS allows data packets to be forwarded at layer-2, switching level- of the OSI model rather than passing upto layer-3. For this reason, it is often referred as operating at layer-2.5

Topology

Instructions

The first step is to configure the interfaces, establish the layer-3 reachability between PE-1 and PE2 via P router using OSPF as IGP protocol
Configure LDP as signalling MPLS protocol on PE1, P1 and PE2 routers. On CE1 and CE2, configure OSPF alone
Post configuration, verify and validate MPLS-LDP neighbourship is up and running b/n PE1 / P1 and P1 / PE2

Configure PE1 router

set interfaces dataplane dp0s4 address 20.1.1.1/24
set interfaces dataplane loopback lo address 1.1.1.1/32
set protocols mpls-ldp address-family ipv4 discovery interface interface dp0s4
set protocols mpls-ldp address-family ipv4 label-policy allocate host-routes 
set protocols mpls-ldp address-family ipv4 transport-address 1.1.1.1
set protocols mpls-ldp lsr-id 1.1.1.1
set protocols ospf area 0 network 20.1.1.0/24
set protocols ospf area 0 network 1.1.1.1/32

Configure P router

set interfaces dataplane dp0s3 address 20.1.1.2/24
set interfaces dataplane dp0s8 address 30.1.1.2/24
set interfaces dataplane loopback lo address 2.2.2.2/32
set protocols mpls-ldp address-family ipv4 discovery interface interface dp0s3
set protocols mpls-ldp address-family ipv4 discovery interface interface dp0s8
set protocols mpls-ldp address-family ipv4 label-policy allocate host-routes 
set protocols mpls-ldp address-family ipv4 transport-address 2.2.2.2
set protocols mpls-ldp lsr-id 2.2.2.2
set protocols ospf area 0 network 20.1.1.0/24
set protocols ospf area 0 network 30.1.1.0/24
set protocols ospf area 0 network 2.2.2.2/32

Configure PE2 router

set interfaces dataplane dp0s8 address 30.1.1.1/24
set interfaces dataplane loopback lo address 3.3.3.3/32
set protocols mpls-ldp address-family ipv4 discovery interface interface dp0s8
set protocols mpls-ldp address-family ipv4 label-policy allocate host-routes 
set protocols mpls-ldp address-family ipv4 transport-address 3.3.3.3
set protocols mpls-ldp lsr-id 3.3.3.3
set protocols ospf area 0 network 30.1.1.0/24
set protocols ospf area 0 network 3.3.3.3/32

Validation

show protocols mpls-ldp neighbor

show protocols mpls-ldp ipv4 interface

show protocols mpls-ldp ipv4 discovery

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Example setting up MPLS-LDP