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What is LD/RD on bfd?


Hi All,


I am curious about explaination of LD/RD on BFD, Could someone explain it?


Any suggestion will be very appreciated, Thank you!

3 Replies 3




bfd.LocalDiscr :-

The local discriminator for this BFD session, used to uniquely
identify it. It MUST be unique across all BFD sessions on this
system, and nonzero. It SHOULD be set to a random (but still
unique) value to improve security. The value is otherwise outside
the scope of this specification.


bfd.RemoteDiscr :-

The remote discriminator for this BFD session. This is the
discriminator chosen by the remote system, and is totally opaque
to the local system. This MUST be initialized to zero. If a
period of a Detection Time passes without the receipt of a valid,
authenticated BFD packet from the remote system, this variable
MUST be set to zero.


Please mark as a solve and hit helpful button, if you got your answer.



Rohit Raj


Rohit Raj

Hi Rohit,


Thanks for your explaination, Where I can find this explaination? URL, docs or blog maybe?


Best Regards,


if we talk about the LD and RD- LD is "my discriminator" and RD is "your discriminator".
now To better understand how BFD is implemented, consider an example. Imagine two routers, each of which runs EIGRP, connected over a common medium. Both routers have just started up, so no BFD session has been established.

In each router, EIGRP informs the BFD process of the IP address of the neighbor that it needs to monitor. It is important to note that BFD does not discover its peers dynamically. It relies on the configured routing protocols to tell it which IP addresses to use and which peer relationships to form.

BFD on each router will form a BFD control packet. These packets are sent at a minimum of one-second intervals* until a BFD session is established. They may cross in transmission, although BFD is designed to adapt to this condition.

The initial packets from either side will be very similar: Vers, Diag, the H, D, P, and F bits will all be set to zero. My Discriminator will be set to a value which is unique on the transmitting router; Your Discriminator is set to zero, because the BFD session has yet to be established**. The values of the TX and RX timers will be set to the values found in the configuration of the device.

After the remote router receives a BFD control packet during the session initiation phase, it will copy the value of the "My Discriminator" field into its own "Your Discriminator" field and set the H ("I Hear You") bit for any subsequent BFD control packets it transmits. Once both systems see their own Discriminators in each other's control packets, the session is "officially" established. Both systems will continue to send at (at least) one-second intervals until they see the appropriate Discriminators in each other's BFD control packets.

The Discriminator values can also be used to multiplex/demultiplex sessions if there are multiple BFD connections between a pair of BFD peers, or to allow the changing of an IP address on a BFD interface without causing the BFD session to be reset.
 initial BFD session setup
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