As described in Section 18.2. - Client Behavior of DHCP - RFC 8415 a client uses the Solicit message to discover DHCP servers configured to assign leases or return other configuration parameters on the link to which the client is attached.
As part of the Solicit message a client uses IA_NA (Identity Association for Non-temporary Addresses) options (see Section 21.4) to request the assignment of non-temporary addresses (Section 18.2.1).
The Identity Association for Non-temporary Addresses Option includes two time intervals:
T1 - The time interval after which the client should contact the server from which the addresses in the IA_NA were obtained to extend the lifetimes of the addresses assigned to the IA_NA; T1 is a time duration relative to the current time expressed in units of seconds. A 4-octet field containing an unsigned integer.
T2 - The time interval after which the client should contact any available server to extend the lifetimes of the addresses assigned to the IA_NA; T2 is a time duration relative to the current time expressed in units of seconds. A 4-octet field containing an unsigned integer.
Although i understand what the times T1/T2 represent, i could not find any information on either default values or an algorithm to set reasonable initial values. Section 14.2. describes cases in which the value could be 0, but only on reception of an IA_NA option and not for an initial Solicit message.
