Re: Speaking of DNS server software...

[William Herrin via NANOG <nanog () lists nanog org>]

On Sun, Aug 10, 2025 at 3:41 AM Etienne-Victor Depasquale
<edepa () ieee org> wrote:
> > Python is, well, Python. It makes as much sense to me to write a DNS
> > server in Perl or Javascript, which is to say: not much.
>
> I don't follow. What's the objection?

Howdy,

On the way in, DNS takes a data buffer delivered from the network
stack and imposes a strange and complex order on the bytes. On the way
back out, it takes complex data and arranges it back into the same
precise structure before passing a simple array of bytes down into the
network stack.

Some languages are well suited to this sort of task. In C, for
example, you mostly just "cast" a well designed data structure from
the pointer to the buffer of bytes. You haven't moved or interpreted
or copied around the data in the buffer, but viola - you can now
directly access the bits and bytes by mnemonic reference. C has
adapted itself to your precise data structure with minimal fuss.

Python doesn't work this way. Its memory management is abstracted away
from the programmer and the programmer does not control its precise
structure. For Python to access a DNS packet, the programmer must pack
and unpack an array of bytes using complex software of their own
devising. You can't just tell Python, "This is the complex data
structure these bytes contain, let me access the data without
unpacking it."

This makes Python code for network handling more complex and much
slower than comparable code for C needs to be. That's not a knock
against Python. Most high-level languages abstract away the exact
handling of data in memory so that programmers can focus on what their
data contains instead of how it's stored. For many programming tasks
that makes programming easier. But not for handling network packets
which differ from the language's internal structure.

Let me leave you with an example to make things more clear. Consider
the following data structures for accessing an IPv4 or IPv6 header in
C:

https://github.com/CAIDA/mrt-tools/blob/main/src/addresses.h

With these data structures you can:

header = (struct ipv4_header*) byte_buffer;
printf ("Don't fragment bit is: %s\n", header->dont_fragment?"set":"unset");

Not only is that code simple, the amount of work the CPU has to do to
execute that code is trivial.

Regards,
Bill Herrin

--
William Herrin
bill () herrin us
https://bill.herrin.us/
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