When interfaces are configured for OSPF and there is a current running FRR configuration that looks like this:
! interface eth0.201 ip ospf authentication message-digest ip ospf message-digest-key 10 md5 ospfmybllnet ! interface eth1 ip ospf bfd ip ospf mtu-ignore ip ospf transmit-delay 5 ! router ospf ospf router-id 172.18.254.201 log-adjacency-changes detail auto-cost reference-bandwidth 100 timers throttle spf 200 1000 10000 passive-interface default no passive-interface eth0.201 network 172.18.201.0/24 area 0 network 172.18.254.201/32 area 0 !
Applying the new FRR configuration of:
! interface eth0.201 ip ospf authentication message-digest ip ospf message-digest-key 10 md5 ospfmybllnet ip ospf hello-interval 10 ip ospf retransmit-interval 5 ip ospf transmit-delay 1 ip ospf dead-interval 40 ! router ospf network 172.18.201.0/24 area 0 network 172.18.254.201/32 area 0 auto-cost reference-bandwidth 100 log-adjacency-changes detail ospf abr-type cisco ospf router-id 172.18.254.201 passive-interface default no passive-interface eth0.201 timers throttle spf 200 1000 10000 !
Will not remove the OSPF interface configuration of eth1 - it continues to stay.