Path: csiph.com!x330-a1.tempe.blueboxinc.net!usenet.pasdenom.info!news.lightlink.com!newsfeed.hal-mli.net!feeder1.hal-mli.net!border3.nntp.dca.giganews.com!Xl.tags.giganews.com!border1.nntp.dca.giganews.com!nntp.giganews.com!local2.nntp.dca.giganews.com!nntp.supernews.com!news.supernews.com.POSTED!not-for-mail NNTP-Posting-Date: Sat, 15 Oct 2011 07:59:17 -0500 Newsgroups: comp.os.linux.networking,alt.os.linux.slackware Subject: Re: Only some IPs accessable? References: <2hpim8x384.ln2@news.roaima.co.uk> From: floyd@apaflo.com (Floyd L. Davidson) Organization: __________ Date: Sat, 15 Oct 2011 04:59:08 -0800 Message-ID: <87ty7av2ar.fld@apaflo.com> User-Agent: gnus 5.10.6/XEmacs 21.4.15/Linux 2.6.27 Cancel-Lock: sha1:FQt5idFEKBmIl5qYmnoFnlCopJQ= MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Lines: 52 X-Trace: sv3-M50bOHJlgYYef+/3tB9qfnEuihRf9SbQF5RyitHMA5R7e7JLosCNRURZUVvgfIOrekZi6UOghwG1AOl!TPZS2al6aEXbkA+EXFFSygFRuPiA/lvg2C9jReyKk5B3OS+a9mPqL4TYUEJ/nQ== X-Complaints-To: www.supernews.com/docs/abuse.html X-DMCA-Complaints-To: www.supernews.com/docs/dmca.html X-Abuse-and-DMCA-Info: Please be sure to forward a copy of ALL headers X-Abuse-and-DMCA-Info: Otherwise we will be unable to process your complaint properly X-Postfilter: 1.3.40 X-Original-Bytes: 3501 Xref: x330-a1.tempe.blueboxinc.net comp.os.linux.networking:701 Henrik Carlqvist wrote: >"NoHtmlMailsPlease" wrote: >> and then I'd like to understand how/why/where linux puts the DNS-IPs >> given by the ISP, and how they are then used. > >The answer is really simple. The DNS servers used are those listed in >/etc/resolv.conf > >How they are used might be a little bit more complicated. Having more than >one DNS server listed in /etc/resolv.conf might be good for redundancy, >but it might also slow things down. For some reason it seems as if the >system waits for all servers to answer even if the first server gives a >correct answer. That should not happen. This quote is from the RESOLV.CONF(5) man page: "On a normally configured system this file should not be necessary. The only name server to be queried will be on the local machine; the domain name is determined from the hostname and the domain search path is constructed from the domain name. The different configuration options are: nameserver Name server IP address Internet address (in dot notation) of a name server that the resolver should query. Up to MAXNS (currently 3, see ) name servers may be listed, one per keyword. If there are multiple servers, the resolver library queries them in the order listed. If no nameserver entries are present, the default is to use the name server on the local machine. (The algorithm used is to try a name server, and if the query times out, try the next, until out of name servers, then repeat trying all the name servers until a maximum number of retries are made.)" The gist is that there is no point in listing more than 3 name servers. But in any event the first one is the only one that will ever be queried if the first query is successful, which also assumes that either there is no local DNS server or that it has failed. The reason for more than one server to be listed is so that a single server need not have 100% availability for DNS to be 100% available. -- Floyd L. Davidson Ukpeagvik (Barrow, Alaska) floyd@apaflo.com