community – How does macOS confirm and replace cached Path MTU for a particular connection

I am investigating how the OS determines and verifies the cached Path MTU (PMTU) for a particular connection. Utilizing netstat -r, I can see the routing tables, and including -l supplies further particulars per connection, together with the PMTU subject.

Here is the way it’s proven:

Vacation spot        Gateway            RT_IFA             Flags        Refs      Use    Mtu          Netif Expire
34.98.77.231       192.168.1.1.       192.168.3.1        UGScg         223        3   1500          en0       

My important questions are:

1. How does the OS confirm that the cached MTU continues to be appropriate?
2. Does the PMTU supported for UDP connections as effectively ?
3. Does the OS periodically implement PMTU discovery by setting the Do not Fragment (DF) bit on outgoing packets to validate the MTU?
4. In that case, below what situations does this verification occur? For instance, is it triggered after a sure time, after a community change, or primarily based on some heuristics?

Thanks!