[bind10-dev] #1534, IPV6_USE_MIN_MTU and similar

[JINMEI Tatuya / 神明達哉]

At Wed, 15 Feb 2012 12:17:39 +0100,
Michal 'vorner' Vaner <michal.vaner at nic.cz> wrote:

> > IMO using the minimum MTU for UDP/IPv6 is the most reasonable default
> > behavior (I don't know how a tftp could be an exception, but even if
> > it could be it seems to be very unlikely we have it in BIND 10), so it
> > makes more sense to do it by default.  If an application specifically
> > wants to perform PMTU discovery for UDP/IPv6 itself (IMO which will be
> > very, very unlikely), that specific application can then disable
> > USE_MIN_MTU, set IPV6_RECVPATHMTU and follow MTU change from ancillary
> > data, etc (again, only very, very few apps would bother to do that).
> 
> Well, I remember Shane telling us about dream where it would contain tftp also,
> so it could do netbooting completely (with assigning names, addresses, providing
> the correct kernels).
> 
> And tftp usually runs on one network (I don't think tftp is ever used for
> anything else but network booting), so the fragment size would not change on the
> path at all, and having larger packets would be better for performance.

I don't remember the dream, but in any case the "dream" sounds nearly
equal to "very, very, unlikely".  And, as far as I know (some?) Cisco
phones use tftp to reach a server in a remote network.

And, most important, the question in this context is which is the more
reasonable default, whether to use minimal MTU for UDP/IPv6.  Even if
we really have one minor example usage of UDP/IPv6 that doesn't need
it, that doesn't automatically support the argument of using it
optionally since we already have a very important usage that
requires it, i.e, DNS.

---
JINMEI, Tatuya
Internet Systems Consortium, Inc.