Posted on May 29, 2020 12:07 am
 |  Asked by Ravicharan Kallem
 |  134 views
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Hello,

We are implementing bfd between Arista to Arista and Arista to Juniper for BGP. We see abnormal behavior with Your Disc and My Disc parameters.

So looking at the bfd neighbors out put. If devices running 4.17.5M, the Your/My Disc numbers are small. If Devices are running 4.20.10M or 4.23.3M then the numbers are very high.

What do those numbers indicate ?

1
Posted by Mark Berly
Answered on May 29, 2020 12:30 am

My Discriminator (My Disc) value is a unique, nonzero discriminator value generated by the transmitting system, used to demultiplex multiple BFD sessions between the same pair of systems.

Your Discriminator (Your Disc) is the discriminator received from the corresponding remote system. This field reflects back the received value of My Discriminator, or is zero if that value is unknown.

Each system MUST choose an opaque discriminator value that identifies each session, and which MUST be unique among all BFD sessions on the system. The local discriminator is sent in the My Discriminator field in the BFD Control packet, and is echoed back in the Your Discriminator field of packets sent from the remote end.

In short they are just a number to allow the identification of multiple BFD sessions.

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

1
Posted by Vikram
Answered on May 29, 2020 12:45 am

Hi Ravicharan,

As per rfc5880 the fields are "My Discriminator" and "Your Discriminator".

 

Quoting the RFC the fields are described as

=====

My Discriminator
A unique, nonzero discriminator value generated by the transmitting system, used to demultiplex multiple BFD sessions between the same pair of systems.

Your Discriminator
The discriminator received from the corresponding remote system. This field reflects back the received value of My Discriminator, or is zero if that value is unknown.

=====

Simply put my understanding is that its a number that uniquely identifies the local and remote endpoint for that respective BFD session and the reason for that is because it is possible that there might be multiple BFD sessions between 2 devices hence there needs to be a way to to uniquely identify the session.

HTH

0
Posted by Ravicharan Kallem
Answered on June 1, 2020 5:10 pm

Thank you Vikram and Mark.

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