Cisco Viptela SDWAN: Bidirectional Forwarding Detection

You may heard about BFD protocol in past as well and we would like to discuss this in Cisco Viptela SDWAN environment. We would go through in brief about BFD first

What is BFD ?
BFD (Bidirectional Forwarding Detection) is a protocol that is able to detect link failures quickly.

BFD in Cisco Viptela devices
With the IPSEC tunnels between the sites/vEdges/cEdges, BFD detects the failures inside the tunnel and is a part of high availability solution. BFD is enabled by default on all Cisco Viptela vEdge routers. There is no way you can disable it.

Fig 1.1- BFD Sessions between vEdges

Note⭐ : Path liveliness and quality measurement detection protocol. It will detects Up/Down, loss/latency/jitter, IPSec tunnel.

Note ⭐ : Runs between all vEdges and with the cEdges or mix devices if they are in one fabric. Operates in echo mode and automatically invoked at IPSec tunnel establishment.

Note ⭐ : BFD Uses hello (up/down) interval and for poll (app-aware) interval and multiplier for detection

Understand the show bfd sessions Command
Generally we used the command "show bfd sessions" on vEdges and "show sdwan bfd sessions" on cEdges. Let's understand this command

vEdges " show bfd sessions"

cEdges " show sdwan bfd sessions"

  • System IP: Peers system-ip
  • Source and remote TLOC Color: This is useful to know what TLOC you are expecting to receive and send.
  • Source IP: It is the private source IP. If you are behind a NAT, this information won't be displayed here (it can be seen with the use of show control local-properties 
  • DST Public IP: It is the destination that the vEdge is using to form the Data Plane tunnel regardless if it is behind NAT or not.
  • DST Public Port: Public NAT-ed port that the vEdge uses in order to form the Data Plane tunnel to the remote vEdge.
  • Transitions: Number of times the BFD session has changed its status, from NA to UP