Summary
In a BGP-only fabric, topology is derived from BGP sessions and BGP routing state rather than from IGP protocols.
This behavior aligns with the IETF document draft-ietf-idr-bgp-ls-bgp-only-fabric.
Use case
it allows to use BGP as IGP and redistribute BGP-LS information.
Additional information
example on FRR:
router bgp 65002 neighbor 192.168.0.1 remote-as 65001 no neighbor 192.168.0.1 enforce-first-as ! address-family link-state link-state distribute bgp-fabric-link-state neighbor 192.168.0.1 activate neighbor 192.168.0.1 route-map all in neighbor 192.168.0.1 route-map all out
vyos config propuse:
set protocols bgp neighbor 192.168.0.1 address-family link-state set protocols bgp neighbor 192.168.0.1 address-family distribute bgp-fabric-link-state instance-id 100 set protocols bgp neighbor 192.168.0.1 address-family route-map XXXX in set protocols bgp neighbor 192.168.0.1 address-family route-map XXXX out set protocols bgp neighbor 192.168.0.1 remote-as '65001' set protocols bgp parameters router-id '3.3.3.3' set protocols bgp system-as '65002'