Date: Wed, 7 May 2008 08:35:49 -0400 From: Bill Moran <wmoran@potentialtech.com> To: Christopher Key <cjk32@cam.ac.uk> Cc: questions@freebsd.org Subject: Re: Underscores in host names Message-ID: <20080507083549.2a4b1d3b.wmoran@potentialtech.com> In-Reply-To: <4821896B.60005@cam.ac.uk> References: <4821896B.60005@cam.ac.uk>
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In response to Christopher Key <cjk32@cam.ac.uk>: > 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. -- Bill Moran http://www.potentialtech.com
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