Controversial SOA values ?

[Kevin Darcy]

wwebb at adni.net wrote:

> > Michael Milligan - Acme Byte & Wire LLC - milli at acmebw.com
>
> > > Likewise, with "notify" updates, why not have a refresh of 1D ?
> >
> > Because NOTIFYs can get dropped, they are just UDP packets. If
> > your zone changes more often than once a day, the refresh needs to
> > be shorter than 1D.
>
> I would be grateful if you could elaborate on "notifys can get dropped, they are just UDP packets." I see no such explanation in the DNS & BIND book.

The _DNS_and_BIND_ book assumes familiarity with TCP/IP networking. UDP is "unreliable"; it has no acknowledgement/retry mechanism built into the protocol (although it is of course possible to layer such a mechanism on top of UDP, as I believe ONC RPC does). So there is a chance of dropped NOTIFY packets and missed updates. The overhead for checking SOA serials is rather small, so why not provide
that extra layer of redundancy?

                                                                                                                        - Kevin