Re: resolvers using non-ephemeral ports

["D. J. Bernstein" <djb@cr.yp.to>]

Mark.Andrews@nominum.com writes:
> don't send a query from echo.

That's a pointless restriction. Forging a DNS packet from an echo server
is no worse than forging a DNS packet from a DNS server.

Neither situation creates a loop as long as servers (1) always set the
response bit in their outgoing packets and (2) never respond to incoming
packets with the response bit set.

Of course, cross-protocol loops are still theoretically possible. The
real problem is that UDP doesn't distinguish clients from servers. One
workaround is to design protocols so that outgoing packets are always
after incoming packets in lexicographic order.

---Dan