Juniper LDP to SR Migration

If you are building a greenfield MPLS network today you'll be faced with a decision to either use a label distribution protocol or to deploy MPLS Segment Routing. Fortunately, brownfield networks can also utilize MPLS-SR and the migration is extremely simple if you are running LDP.

Router configuration from R1

chassis {
    network-services enhanced-ip;
}
interfaces {
    ge-0/0/2 {
        unit 0 {
            family inet {
                address 172.99.0.10/30;
            }
            family mpls;
        }
    }
    ge-0/0/4 {
        unit 0 {
            family inet {
                address 172.99.0.6/30;
            }
            family mpls;
        }
    }
    ge-0/0/5 {
        flexible-vlan-tagging;
        encapsulation flexible-ethernet-services;
        unit 316 {
            encapsulation vlan-bridge;
            vlan-id 316;
        }
    }
    lo0 {
        unit 0 {
            family inet {
                address 10.255.255.101/32;
            }
        }
    }
}
routing-instances {
    EVPN-316 {
        instance-type evpn;
        protocols {
            evpn {
                mac-table-size {
                    300;
                }
                interface-mac-limit {
                    300;
                }
                mac-statistics;
            }
        }
        interface ge-0/0/5.316;
        route-distinguisher 10.255.255.101:316;
        vrf-target target:65000:316;
    }
}
routing-options {
    router-id 10.255.255.101;
    autonomous-system 65000;
}
protocols {
    ospf {
        area 0.0.0.0 {
            interface lo0.0 {
                passive;
            }
            interface ge-0/0/4.0 {
                interface-type p2p;
            }
            interface ge-0/0/2.0 {
                interface-type p2p;
            }
        }
    }
    bgp {
        group ibgp {
            type internal;
            local-address 10.255.255.101;
            log-updown;
            family inet {
                unicast;
            }
            family evpn {
                signaling;
            }
            peer-as 65000;
            local-as 65000;
            neighbor 10.255.255.103;
            neighbor 10.255.255.102;
        }
    }
    ldp {
        interface ge-0/0/2.0;
        interface ge-0/0/4.0;
    }
    mpls {
        interface ge-0/0/2.0;
        interface ge-0/0/4.0;
    }
}

During normal operation, we can expect our loopbacks to be in the inet.3 table via LDP discovery.

root> show route 10.255.255.102 table inet.3      

inet.3: 2 destinations, 4 routes (2 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

10.255.255.102/32  *[LDP/9] 00:02:11, metric 1
                    >  to 172.99.0.5 via ge-0/0/4.0, Push 25

And when we turn on OSPF-SR, we can expect to now learn the same route but via L-OSPF.

root> show route 10.255.255.102 table inet.3      

inet.3: 2 destinations, 4 routes (2 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

10.255.255.102/32  *[LDP/9] 00:02:11, metric 1
                    >  to 172.99.0.5 via ge-0/0/4.0, Push 25
                    [L-OSPF/10/5] 00:01:05, metric 2
                    >  to 172.99.0.5 via ge-0/0/4.0, Push 5100

So how do we turn on OSPF-SR?

set protocols ospf source-packet-routing node-segment ipv4-index 100

Verification before disabling LDP

1. For each ingress router, check the inet.3 table for the L-OSPF routes
2. For each transit router, check the mpls.0 table for the corresponding labels