PTM - Prescriptive Topology Manager

Cumulus Linux - PTMD ensure actual virtual/physical links connected to the right place. A script execute at /etc/ptm.d/if-topo-pass / if-topo-failfor if each interface that encounters a flip. It uses LLDP reading and advertising interface metadata like show cdp neighbor To enable the service globally by sudo vtysh -c 'conf t' -c 'ptm-enable', show ptm status sudo vtysh -c 'show interface swp1'. Modify these dot file as needed /etc/ptmd./topologoy.dot and reload sudo systemctl force-reload ptmd.service .

graph G {

 # Spine and leaf ToR links
 "leaf01":"swp86" -- "spine01":"swp1"
 "leaf02":"swp86" -- "spine01":"swp2"
 "leaf03":"swp86" -- "spine01":"swp3"
}
Note: this version of vtysh never writes vtysh.conf
Building Configuration...
Integrated configuration saved to /etc/quagga/Quagga.conf

spine01# show interface swp1
Interface swp1 is up, line protocol is up
  **PTM status: pass**
  vrf: Default-IP-Routing-Table
  index 4 metric 0 mtu 1500
  flags: <UP,BROADCAST,RUNNING,MULTICAST>
  Type: Ethernet
  Interface Type Other
  ND advertised reachable time is 0 milliseconds
  ND advertised retransmit interval is 0 milliseconds
  ND router advertisements sent: 115 rcvd: 114
  ND router advertisements are sent every 10 seconds
  Neighbor address(s):
  inet6 fe80::4638:39ff:fe00:5b/128
../../../_images/ptmctl.png

BFD - https://tools.ietf.org/html/rfc5880

LLDP - https://en.wikipedia.org/wiki/Link_Layer_Discovery_Protocol