Automatically calculate the values for options 58 and 59
name: Automatically calculate the values for options 58 and 59 about: This is a request to have it be possible for Kea to calculate and send the values for renew-timer and rebind-timer (T1 and T2) using 0.5 * duration_of_lease, and 0.875 * duration_of_lease, respectively
Some initial questions This is a request from a customer, per ticket #13977
At the moment, ISC Kea defaults to not sending T1 and T2, although they can be specified explicitly using optional renew-timer and rebind-timer. What is being requested is another option in which we ask Kea to automate this - i.e. to calculate them based on the lease time being offered using the default behaviour that clients should be adopting as noted above.
The reason for requesting this is that: a) Other DHCP servers (e.g. Nominum) do this by default (even though ISC DHCP does not) b) It is a potential mitigation for clients that are not fully RFC-compliant
Describe the solution you'd like In it's simplest form, a blanket option to request that Kea calculate the timers and send them for any lease offer, calculations being appropriate to that specific offer.
More flexibility might be appreciated however - for example being able to set this per subnet, pool or shared-network to override a global setting which might be different.
For full flexibility, the option could perhaps also have an alternative syntax in which it accepts the percentages as an override to the default of .5 and .875 - although this might be overkill - would anyone want these to be different? (Perhaps leading up to a pool/servers migration maybe?)
Describe alternatives you've considered Currently, the only way to ensure that ISC Kea sends the values of T1 and T2 that are wanted is to configure them explicitly, it's not possible to have them sent automatically
Additional context Note that this may be regarded as a compatibility issue by anyone migrating to ISC Kea from another DHCP server implementation that does automatically send T1 and T2.