Barry Margolin writes:

> When a refresh occurs due to the Refresh timer going off, it will check
> each master serially, and pull a transfer from one if it has a higher
> serial number than the local copy. It doesn't try them both
> concurrently.

it will try them all, transfer only from a master offering the best currently
available serial number. this is tricky given "sequence number arithmetic"
and 32-bit rounding.
Paul Vixie