Hash: RIPEMD160

Bill Moran wrote:
> In response to Christopher Key <[EMAIL PROTECTED]>:
>> Hello,
>> I've a host on the network called "GC100_000C1E00AC3F_GlobalCache", and 
>> I'm getting interesting behaviour when I try to do DNS lookups on it.
>> Under FreeBSD, ping fails with 'Unknown server error'(distinct from the 
>> standard 'Unknown host'), and nslookup succeeds.  OSX and Windows 
>> machines will do a DNS lookup on it quite happily
>> The best explanation I can manage is that ping etc. are using different 
>> code from nslookup, and only nslookup is allowing the underscores within 
>> the hostname.
>> Is this behaviour by design?  My understanding is that underscores are 
>> not strictly permitted, but that most implementations choose to allow 
>> them unless there's a specific reason not to.
> I had this discussion with some colleagues a short time back.  Our
> conclusion (based on some research and experimentation):
> 1) Underscores are not valid in domain names.
> 2) _most_ DNS systems will work with them anyway.
> 3) Just enough DNS systems don't work with _, that it's a really bad
>    idea to use them in domain names.

DNS is perfectly happy with underscores in RRs generally -- it's just forbidden
for them to appear in hostnames in the DNS specifically.  This is to distinguish
between hostnames and other data such as SRV records.



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