On Oct 11, 2025, at 6:46 AM, Deb Cooley via Datatracker <[email protected]>
wrote:
> Section 10: Normally I would expect to see how the provision of symmetric
> keys
> (for keyed hashes, etc.) is accomplished. According to RFC 5880, keys are
> shipped across the network in the clear via the local/remote discriminator
> field.
The discriminator field has nothing to do with keys. From 5880, the local
discriminator field is defined 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.
i.e. is it an opaque token which is used to discriminate between different
sessions.
Other than identifying a particular session, the discriminator has no meaning
or interpretation.
Over time. one pair of peers can establish multiple sessions between them.
Each different session will have different discriminators. However, all of
those sessions will typically share the same secret key for authentication.
> This helps the attacker. Please address this issue here, or point back
> to the relevant section in RFC 5880 where the mitigation is outlined.
The keys are distributed offline. 5880 Section 6.7.3 says about MD5 methods:
In these methods of
authentication, one or more secret keys (with corresponding key IDs)
are configured in each system.
i.e. the administrator configures the keys out of band. RFC5880 makes no
provisions for exchanging key values in BFD.
Alan DeKok.
