My configuration:

MX1:
set system host-name MX1
set interfaces ge-0/0/0 unit 0 family inet address 10.0.0.0/31
set interfaces ge-0/0/1 unit 0 family inet address 11.0.0.0/31
set interfaces lo0 unit 0 family inet address 1.1.1.1/32
set protocols ospf area 0.0.0.0 interface ge-0/0/0.0 interface-type p2p
set protocols ospf area 0.0.0.0 interface ge-0/0/1.0 interface-type p2p

MX2:
set system host-name MX2
set interfaces ge-0/0/0 unit 0 family inet address 10.0.0.1/31
set interfaces ge-0/0/1 unit 0 family inet address 12.0.0.0/31
set interfaces ge-0/0/2 unit 0 family inet address 20.0.0.0/31
set interfaces lo0 unit 0 family inet address 2.2.2.2/32
set protocols ospf area 0.0.0.0 interface ge-0/0/0.0 interface-type p2p
set protocols ospf area 0.0.0.0 interface ge-0/0/2.0 interface-type p2p
set protocols ospf area 0.0.0.1 nssa default-lsa default-metric 1
set protocols ospf area 0.0.0.1 nssa default-lsa metric-type 1
set protocols ospf area 0.0.0.1 nssa no-summaries
set protocols ospf area 0.0.0.1 interface ge-0/0/1.0 interface-type p2p

MX3:
set system host-name MX3
set interfaces ge-0/0/0 unit 0 family inet address 13.0.0.0/31
set interfaces ge-0/0/1 unit 0 family inet address 11.0.0.1/31
set interfaces ge-0/0/2 unit 0 family inet address 20.0.0.1/31
set protocols ospf area 0.0.0.0 interface ge-0/0/1.0 interface-type p2p
set protocols ospf area 0.0.0.0 interface ge-0/0/2.0 interface-type p2p
set protocols ospf area 0.0.0.2 nssa default-lsa default-metric 1
set protocols ospf area 0.0.0.2 nssa default-lsa metric-type 1
set protocols ospf area 0.0.0.2 nssa no-summaries
set protocols ospf area 0.0.0.2 interface ge-0/0/0.0 interface-type p2p

MX4:
set system host-name MX4
set interfaces ge-0/0/0 unit 0 family inet address 13.0.0.1/31
set interfaces ge-0/0/1 unit 0 family inet address 12.0.0.1/31
set interfaces lo0 unit 0 family inet address 100.100.100.100/32
set protocols ospf export external-route-to-lo0
set protocols ospf area 0.0.0.1 nssa
set protocols ospf area 0.0.0.1 interface ge-0/0/1.0 interface-type p2p
set protocols ospf area 0.0.0.2 nssa
set protocols ospf area 0.0.0.2 interface ge-0/0/0.0 interface-type p2p
set policy-options policy-statement external-route-to-lo0 from protocol direct
set policy-options policy-statement external-route-to-lo0 from interface lo0.0
set policy-options policy-statement external-route-to-lo0 then external type 1
set policy-options policy-statement external-route-to-lo0 then accept