Comment 1 for bug 1927097

That is due to this code here https://github.com/ceph/ceph/blob/master/src/cephadm/cephadm#L4638-L4661

which tries to parse 'ip route ls'. In a BGP/BFD environment this is more complex than expected:
[root@ctrl-1-0 sbin]# ip r
default proto bgp src 172.30.1.1 metric 20
        nexthop via 100.64.0.1 dev enp3s0 weight 1
        nexthop via 100.65.1.1 dev enp2s0 weight 1
100.64.0.0/30 dev enp3s0 proto kernel scope link src 100.64.0.2
100.65.1.0/30 dev enp2s0 proto kernel scope link src 100.65.1.2
192.168.1.0/24 dev enp1s0 proto kernel scope link src 192.168.1.164
192.168.2.0/24 via 192.168.1.1 dev enp1s0
192.168.3.0/24 via 192.168.1.1 dev enp1s0
192.168.4.0/24 via 192.168.1.1 dev enp1s0