Bidirectional Forwarding Detection (BFD)

Bidirectional Forwarding Detection (BFD) is a network protocol used to detect link failure between two nodes. This is great features used for link detection as it even detect failure for you on Layer-1 where mostly detection is not possible like on VC, tunnels, MPLS-LSP, Ethernet etc.

When BFD session is establishes between two nodes, & if there are more than twlo links exists b/w that two nodes so BFD can be used to monitor the session for these two nodes. BFD does not have a discovery mechanism, sessions must be explicitly configured between endpoints. For example, on Huawei NE40E, we can do like:

bfd to-NameOfNode-001 bind peer-ip default-ip interface GigabitEthernet1/1/1
discriminator local 809
discriminator remote 908
min-tx-interval 60
min-rx-interval 60
process-interface-status
commit

BFD may &/or can be used on many different transport mechanisms and layers. For this it needs to be encapsulated by whatever transport it uses. For example, MPLS-LSP, OSPF, IS-IS Protocols that support some form of adjacency setup.

BFD can be used in either asynchronous mode and demand mode.

I hope this will be informative for you.

Cheers :)

BFD Session status Changes to Down & Up

While working on DataCom Network (composed of hundreds of NE routers, configured with MPLS, IS-IS, QoS, MPLS-VPN, MPLS-TE, BGP and list goes on and on……..!, I saw this alarm “BFD Session status Changes to down” and “BFD Session status changes to up”. After doing some research, studying and help, I came to know about the root cause and main reason for this alarm.

There can be different reason for alarm to appear:

1. The status of the interface goes down on which the BFD session is established between the two peers.

2. The BFD peer session is deleted or shutdown explicitly.

3. The link is not able to forward packets because of congestion or may be the link status is down.

In my case it was NSA (Non-Service Affecting) and I just need to confirm the status so for that we need to remember few commands which are:


display interface [interface name]

display bfd session all

There are bundle of more commands, if you need any help regarding that please feel free to reach me.

Note: If you are not familiar about BFD? Wait for my next blog on BFD

I Hope this will be informative for you :)