Maximum number of DNS servers

[Shane Kerr]

I made a quick scan of the ARIN database, and here are the counts of
number of hosts for networks:

0 hosts = 343044
1 host  = 359
2 hosts = 26630
3 hosts = 5646
4 hosts = 2042
5 hosts = 641
6 hosts = 165
7 hosts = 10
8 hosts = 1

(Not sure about those 359 entries with one host.  There's not much we can
do about those entries, except perhaps contact the adminstrators and ask
for clean up.)

Currently the list of host handles must fit in a fixed-size field of the
database, so the number of hosts is limited, but it depends on the actual
handles of the host records (that is, A-HST and B-HST might fit where
SOMEOTHER-HST might not).

Choosing the smaller limit does save us a couple of Kbyte of space, but
what I'm really thinking there are perhaps user interface designs that are
practicable with sets of 10 that aren't really feasable with sets of 100.
The reason the number 10 came up is that it's handy in an SQL database,
but the advantage lies in dealing with the group.  If we have a smallish
limit, we can build HTML forms and such around that limit.  If there is no
such limit, then a more sophisticated (and possibly cumbersome and
confusing) interface needs to be designed:

     +--------------------------------+
  1. | NS.FOO.BAR.COM                 |
     +--------------------------------+
     +--------------------------------+
  2. | NS2.FOO.BAR.NET                |
     +--------------------------------+
     +--------------------------------+
  3. | NS3.FOO.BAR.ORG_               |
     +--------------------------------+
  
       +------------+   +------+
       | Add Server |   | Done |
       +------------+   +------+

The user would either need to run a fairly complicated JavaScript program
or send an HTML form to the server multiple times to build a list.  Not
that this is necessarily so bad, but there it is.  Of course, the
interfaces can have limits that the database itself does not.

>From a programmers perspective, there are only 3 numbers: 0, 1, and many.
:)

--
Shane Kerr <kerr at arin.net>
Senior Software Engineer
American Registry for Internet Numbers (ARIN)
+1 703-227-9877

On Wed, 26 Apr 2000, Danny McPherson wrote:

> I agree.  If choosing the larger value doesn't impose any additional
> constraint then it would certainly be the optimal solution.  It's not
> as if you're attempting to reduce protocol overhead or the like.
> 
> -danny
> 
> > I'm not certain if any studies have been made regarding any "ceilings of
> > effectiveness" for NS delegation.  Barring any such technical difficulty
> > or BCP quoting a number beyond which it becomes stupid to add more, I'm
> > stunned that such an arbitrary limit would even be considered.  Should I
> > ask why the database system case how many digits [character
> > representations] there are rather than a true value [bit-size of the
> > actual value].  
> > 
> > Just because I can't think of a need for more than 5-7 for a given
> > netblock doesn't mean someone else won't.  If you have to make this kind
> > of arbitrary, display-oriented (rather than value-oriented) cutoff,
> > Internet experience dictates to go with the larger of your choices.  
> > 
> > Cheers,
> > 
> > Joe
> > --
> > Joe Provo                                            Voice  508.486.7471
> > Director, Internet Planning & Design                 Fax    508.229.2375
> > Network Deployment & Management, RCN                 <joe.provo at rcn.com>