[PLUG] How many ways to write a FQDN???

Frank Hunt linux at frankhunt.com
Sat Jun 9 10:42:02 UTC 2007


How about co.washington.or.us. ?

You are correct in that the maximum permitted length of an FQDN is 255 
bytes, with an additional restriction to 63 bytes for each label within 
the domain name.  So, yes - it does include the periods (4 * 63 +3 = 255)

someone wrote:
> How many ways can a fully qualified DNS domain name be written that
> are resolveable?
> 
> I know of only this one:
> 
> some.name.com
> 
> Are there other possibilities that are common in SMTP email headers?
> 
> On the subject, what is the maximum nth level subdomain for DNS names?
> I know it's possibly to get to 4 levels.  For example.
> 
> For some.name.com, it has a first level of the root domain, a second  
> level of the .com sub domain, a third level of the .name subdomain,  
> and fourth level
> of the some. host name.
> 
> If I know the longest name that DNS can do, that makes it potentially
> possible to avoid doing unnecessary DNS searches on bogus FQDN strings.
> 
> RFC 1035 suggest 255 octets which means, I think, that a fully qualified
> domain name can have up to 255 characters in it.  Whether that includes
> the
> periods or not, I'm not sure.
> 
>       Michael C. Robinson
> 
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> 

-- 
frank hunt
PLUG member-in-absentia
confused linux admin
part time windows(r) washer
rochester hills, mi



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