FQDN

[John Hascall]

> phaniraj ranganath wrote:
> >
> > I want to know why the FQDN cann't be more than 256 characters
> > & the name at any node in Internet Domain name space cann't be more
> > than 63 characters?
> 
> The length limit is 255 not 256 I believe.
> 
> The reason is that rfc1034 says so, read the rfc's for more background,
> but it says "to ease implementation".
> 
> > Is there any restriction in the number of levels
> > in Internet i.e. from root servers how many levels can the structure
> > of internet span?
> 
> As far as I know only the implied limit from the length restrictions
> which I make 128 labels of one character.
> 
> However you would need to check the resolution algorithms to see if this
> would break the resolvers in common use, as I suspect some might give up
> before they had got to resolving a name involving substantially more
> levels than possible. It is possible one of the RFCs implies a lower limit.

Experimentally, stupidly long names seem to work in at least some cases:

% nslookup
> a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a
Server:  netreg-1.ait.iastate.edu
Address:  129.186.1.16

Name:    a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a.a
Address:  129.186.1.16


Why somebody would want to actually use such a thing escapges me though,
as the whole point of DNS is that names are easier than numbers.

John