When VyOS has a PPPoE interface configured which receives the default route for the system - changes to the protocols static tree - mainly a deletion will isolate the system as the default route is deleted.
vyos@vyos:~$ show ip route
Codes: K - kernel route, C - connected, L - local, S - static,
R - RIP, O - OSPF, I - IS-IS, B - BGP, E - EIGRP, N - NHRP,
T - Table, v - VNC, V - VNC-Direct, A - Babel, F - PBR,
f - OpenFabric, t - Table-Direct,
> - selected route, * - FIB route, q - queued, r - rejected, b - backup
t - trapped, o - offload failure
IPv4 unicast VRF default:
S>* 0.0.0.0/0 [1/0] is directly connected, pppoe0, weight 1, 00:00:19
C>* 172.16.33.0/24 is directly connected, eth0.10, weight 1, 00:00:22
L>* 172.16.33.202/32 is directly connected, eth0.10, weight 1, 00:00:22
C>* 172.18.202.0/24 is directly connected, eth0.202, weight 1, 00:00:21
L>* 172.18.202.10/32 is directly connected, eth0.202, weight 1, 00:00:21
L * 172.18.254.202/32 is directly connected, dum0, weight 1, 00:00:23
C>* 172.18.254.202/32 is directly connected, dum0, weight 1, 00:00:23
C>* 192.0.2.1/32 is directly connected, pppoe0, weight 1, 00:00:19
L>* 192.0.2.133/32 is directly connected, pppoe0, weight 1, 00:00:19Add a static blackhole route to the system
vyos@vyos:~$ configure
vyos@vyos# set protocols static route 10.0.0.0/8 blackhole
vyos@vyos# commit
vyos@vyos# run show ip route
Codes: K - kernel route, C - connected, L - local, S - static,
R - RIP, O - OSPF, I - IS-IS, B - BGP, E - EIGRP, N - NHRP,
T - Table, v - VNC, V - VNC-Direct, A - Babel, F - PBR,
f - OpenFabric, t - Table-Direct,
> - selected route, * - FIB route, q - queued, r - rejected, b - backup
t - trapped, o - offload failure
IPv4 unicast VRF default:
S>* 0.0.0.0/0 [1/0] is directly connected, pppoe0, weight 1, 00:00:35
S>* 10.0.0.0/8 [1/0] unreachable (blackhole), weight 1, 00:00:03
C>* 172.16.33.0/24 is directly connected, eth0.10, weight 1, 00:00:38
L>* 172.16.33.202/32 is directly connected, eth0.10, weight 1, 00:00:38
C>* 172.18.202.0/24 is directly connected, eth0.202, weight 1, 00:00:37
L>* 172.18.202.10/32 is directly connected, eth0.202, weight 1, 00:00:37
L * 172.18.254.202/32 is directly connected, dum0, weight 1, 00:00:39
C>* 172.18.254.202/32 is directly connected, dum0, weight 1, 00:00:39
C>* 192.0.2.1/32 is directly connected, pppoe0, weight 1, 00:00:35
L>* 192.0.2.133/32 is directly connected, pppoe0, weight 1, 00:00:35Delete recently added 10.0.0.0/8 blackhole route from the RIB
vyos@vyos# delete protocols static vyos@vyos# commit
Check FIB - also the default 0.0.0.0/0 route is gone.
vyos@vyos# run show ip route
Codes: K - kernel route, C - connected, L - local, S - static,
R - RIP, O - OSPF, I - IS-IS, B - BGP, E - EIGRP, N - NHRP,
T - Table, v - VNC, V - VNC-Direct, A - Babel, F - PBR,
f - OpenFabric, t - Table-Direct,
> - selected route, * - FIB route, q - queued, r - rejected, b - backup
t - trapped, o - offload failure
IPv4 unicast VRF default:
C>* 172.16.33.0/24 is directly connected, eth0.10, weight 1, 00:00:45
L>* 172.16.33.202/32 is directly connected, eth0.10, weight 1, 00:00:45
C>* 172.18.202.0/24 is directly connected, eth0.202, weight 1, 00:00:44
L>* 172.18.202.10/32 is directly connected, eth0.202, weight 1, 00:00:44
L * 172.18.254.202/32 is directly connected, dum0, weight 1, 00:00:46
C>* 172.18.254.202/32 is directly connected, dum0, weight 1, 00:00:46
C>* 192.0.2.1/32 is directly connected, pppoe0, weight 1, 00:00:42
L>* 192.0.2.133/32 is directly connected, pppoe0, weight 1, 00:00:42