From owner-freebsd-questions@FreeBSD.ORG Wed May 7 13:05:04 2008 Return-Path: Delivered-To: questions@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 128FA106564A for ; Wed, 7 May 2008 13:05:04 +0000 (UTC) (envelope-from m.seaman@infracaninophile.co.uk) Received: from smtp.infracaninophile.co.uk (gate6.infracaninophile.co.uk [IPv6:2001:8b0:151:1::1]) by mx1.freebsd.org (Postfix) with ESMTP id 7F9638FC16 for ; Wed, 7 May 2008 13:05:03 +0000 (UTC) (envelope-from m.seaman@infracaninophile.co.uk) Received: from lack-of-gravitas.thebunker.net (gateway.ash.thebunker.net [213.129.64.4]) (authenticated bits=0) by smtp.infracaninophile.co.uk (8.14.2/8.14.2) with ESMTP id m47D4l95005889 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Wed, 7 May 2008 14:04:54 +0100 (BST) (envelope-from m.seaman@infracaninophile.co.uk) X-DKIM: Sendmail DKIM Filter v2.5.5 smtp.infracaninophile.co.uk m47D4l95005889 DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=infracaninophile.co.uk; s=200708; t=1210165494; bh=EMkCBG898BsxYE K4CadjFgEIgpNNQJ6i2aBNzEWfvIE=; h=Message-ID:Date:From:MIME-Version: To:CC:Subject:References:In-Reply-To:Content-Type: Content-Transfer-Encoding:Cc:Content-Type:Date:From:In-Reply-To: Message-ID:Mime-Version:References:To; z=Message-ID:=20<4821A8EE.8 030704@infracaninophile.co.uk>|Date:=20Wed,=2007=20May=202008=2014: 04:46=20+0100|From:=20Matthew=20Seaman=20|Organization:=20Infracaninophile|User-Agent:=20Thunderbird= 202.0.0.14=20(X11/20080506)|MIME-Version:=201.0|To:=20Bill=20Moran= 20|CC:=20Christopher=20Key=20,=20questions@freebsd.org|Subject:=20Re:=20Underscores=20in=20 host=20names|References:=20<4821896B.60005@cam.ac.uk>=20<2008050708 3549.2a4b1d3b.wmoran@potentialtech.com>|In-Reply-To:=20<20080507083 549.2a4b1d3b.wmoran@potentialtech.com>|X-Enigmail-Version:=200.95.0 |Content-Type:=20text/plain=3B=20charset=3DUTF-8|Content-Transfer-E ncoding:=207bit; b=xcNuzZmYthg36VBBb56vVtAJa8GjsxWZrCYzqHKnc8VXKBOb sSC1RohW41hWkpYAB4IlKKHivmgdx/AmMXyf5DD0W5ZPBA84THNw2Y0wt/I4+aDAKn5 62OP4NvEZXlT66Dy/GSWC6Z+MvoemKEFcDSfyb92TMGl2gw4ZFGEOM7Y= Message-ID: <4821A8EE.8030704@infracaninophile.co.uk> Date: Wed, 07 May 2008 14:04:46 +0100 From: Matthew Seaman Organization: Infracaninophile User-Agent: Thunderbird 2.0.0.14 (X11/20080506) MIME-Version: 1.0 To: Bill Moran References: <4821896B.60005@cam.ac.uk> <20080507083549.2a4b1d3b.wmoran@potentialtech.com> In-Reply-To: <20080507083549.2a4b1d3b.wmoran@potentialtech.com> X-Enigmail-Version: 0.95.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.0 (smtp.infracaninophile.co.uk [81.187.76.162]); Wed, 07 May 2008 14:04:54 +0100 (BST) X-Virus-Scanned: ClamAV version 0.93, clamav-milter version 0.93 on happy-idiot-talk.infracaninophile.co.uk X-Virus-Status: Clean X-Spam-Status: No, score=-2.6 required=5.0 tests=AWL,BAYES_00,DKIM_SIGNED, DKIM_VERIFIED,SPF_FAIL autolearn=no version=3.2.4 X-Spam-Checker-Version: SpamAssassin 3.2.4 (2008-01-01) on happy-idiot-talk.infracaninophile.co.uk Cc: questions@freebsd.org, Christopher Key Subject: Re: Underscores in host names X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 07 May 2008 13:05:04 -0000 -----BEGIN PGP SIGNED MESSAGE----- Hash: RIPEMD160 Bill Moran wrote: > In response to Christopher Key : > >> 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. Cheers, Matthew - -- Dr Matthew J Seaman MA, D.Phil. Flat 3 7 Priory Courtyard PGP: http://www.infracaninophile.co.uk/pgpkey Ramsgate Kent, CT11 9PW, UK -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.9 (FreeBSD) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iEYEAREDAAYFAkghqO4ACgkQ3jDkPpsZ+VZBewCdHQWo8t2uUoAktf84NdTG6CKX FIwAoIBMMlu9k6+8N1Wypz0Wm33v7VuD =fU7u -----END PGP SIGNATURE-----