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From: cdp@njit.edu (Chris Peckham)
Subject: comp.protocols.tcp-ip.domains Frequently Asked Questions (FAQ) (Part 2 of 2)
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Revision: 1.5 1995/05/12 18:50:41


This FAQ is edited and maintained by Chris Peckham, <cdp@njit.edu>. 
The latest version may always be found for anonymous ftp from

    ftp://rtfm.mit.edu/pub/usenet/news.answers/internet/tcp-ip/domains-faq
    ftp://ftp.njit.edu/pub/dns/Comp.protocols.tcp-ip.domains.FAQ

If you can contribute any answers for items in the TODO section, please do
so by sending e-mail to domain-faq@njit.edu !  If you know of any items that 
are not included and you feel that they should be,  send the relevant
information to domain-faq@njit.edu.


------------------------------

Date: Fri May 12 14:41:47 EDT 1995
Subject: Table of Contents

Table of Contents
=================
Part 1
------
   0. TO DO
   1. INTRODUCTION / MISCELLANEOUS
      1.1  What is this newsgroup ?
      1.2  More information
      1.3  What is BIND and where is the latest version of BIND ?
      1.4  How can I find the route between systems ?
      1.5  Finding the hostname if you have the tcp-ip address
      1.6  How to register a domain name
      1.7  Change of Domain name
      1.8  How memory and CPU does DNS use ?
      1.9  Other things to consider when planning your servers  
      1.10 Proper way to get NS and reverse IP records into DNS
      1.11 How to get my address assign from NIC?
      1.12 Is there a block of private IP addresses I can use?
      1.13 Cache failed lookups
      1.14 What does an NS record really do ?
      1.15 DNS ports
      1.16 Obtaining the latest cache file 
   2. UTILITIES
      2.1  Utilities to administer DNS zone files
      2.2  DIG - Domain Internet Groper
      2.3  DNS packet analyzer
      2.4  host 
      2.5  Programming with DNS
      2.6  A source of information relating to DNS
   3. DEFINITIONS
      3.1  TCP/IP Host Naming Conventions
      3.2  Slaves and servers with forwarders
      3.3  When is a server authoritative?
      3.4  Underscore in host-/domain names
      3.5  Lame delegation
      3.6  What does opt-class field do?
      3.7  Top level domains
      3.8  Classes of networks
      3.9  What is CIDR ?
      3.10 What is the rule for glue ?

Part 2
------
   4. CONFIGURATION
      4.1  Changing a Secondary server to a Primary
      4.2  How do I subnet a Class B Address ?
      4.3  Subnetted domain name service
      4.4  Recommended format/style of DNS files
      4.5  DNS on a system not connected to the Internet
      4.6  Multiple Domain configuration
      4.7  wildcard MX records
      4.8  How to identify a wildcard MX record
      4.9  Why are fully qualified domain names recommended ?
      4.10 Distributing load using named
      4.11 Order of returned records
      4.12 resolv.conf 
      4.13 Delegating authority 
      4.14 DNS instead of NIS on a Sun OS 4.1.x system
   5. PROBLEMS
      5.1  No address for root server
      5.2  Error - No Root Nameservers for Class XX
      5.3  Bind 4.9.x and MX querying?
      5.4  Some root nameservers don't know localhost
      5.5  MX records and CNAMES and separate A records for MX targets
      5.6  NS is a CNAME
      5.7  Nameserver forgets own A record
      5.8  General problems (core dumps !)
      5.9  malloc and DECstations
   6. ACKNOWLEDGEMENTS

------------------------------

Date: Fri Dec  2 15:31:06 EST 1994
Subject: Q4.1 - Changing a Secondary server to a Primary

Q: Do I need to do anything special when I change a server from a secondary 
   to a primary ?
 
A: For 4.8.3,  it's prudent to kill and restart following any changes to
   named.boot.
 
   In BIND 4.9.3, you only have to kill and restart named if you change
   a primary zone to a secondary or v-v, or if you delete a zone and
   remain authoritative for its parent.  Every other case should be
   taken care of by a HUP.  (Ed. note: 4.9.3b9 may still require you to
   kill and restart the server due to some bugs in the HUP code).

   You will also need to update the server information on the root servers.
   You can do this by filing a new domain registration form to inform 
   InterNIC of the change.  They will then update the root server's SOA
   records.  This process usually takes 10-12 business days after they
   receive the request.

-------------------------------

Date: Fri Apr 28 13:34:52 EDT 1995
Subject: Q4.2 - How do I subnet a Class B Address ?

Q: I just received a Class B internet address and I am wondering where to
   get an RFC or other information on how to properly to the TCP/IP
   sub-netting.
 
A: That you need to subnet at all is something of a misconception.  You
   can also think of a class B network as giving you 65,534 individual
   hosts, and such a network will work. You can also configure your
   class B as 16,384 networks of 2 hosts each.  That's obviously not
   very practical, but it needs to be made clear that you are not
   constrained by the size of an octet (remember that many older
   devices would not work in a network configured in this manner).
 
   So, the question is: why do you need to subnet?   One reason is that
   it is easier to manage a subnetted network, and in fact, you can
   delegate the responsibility for address space management to local
   administrators on the various subnets.  Also, IP based problems will
   end up localized rather than affecting your entire network.
   
   If your network is a large backbone with numerous segments
   individually branching off the backbone, that too suggests
   subnetting.

   Subnetting can also be used to improve routing conditions.

   You may wish to partition your network to disallow certain protocols 
   on certain segments of your net.  You can, for example, restrict IP or
   IPX to certain segments only by adding a router routing high level 
   protocols, and across the router you may have to subnet. 

   Finally, as far as how many subnets you need depends on the answer to
   the above question.  As far as subnet masks are concerned, the mask
   can be anything from 255.0.0.0 to 255.255.255.252.  You'll probably be
   looking at 9 or 10 bits for the subnet (last octet 128 or 192
   respectively).  RFC1219 discusses the issue of subnetting very well 
   and leaves the network administrator with a large amount of flexibility
   for future growth.


------------------------------
 
Date: Sun Nov 27 23:32:41 EST 1994
Subject: Q4.3 -Subnetted domain name service

Q: After doing some reading (DNS and BIND, Albitz&Liu), I don't really
   find any examples of handling subnetted class C networks as separate
   DNS domains.
 
A: This is possible, just messy.   You need to delegate down to the
   fourth octet, so you will have one domain per IP address !  Here is
   how you can subdelegate a in-addr.arpa address for non-byte aligned 
   subnet masks:

   Take as an example the net 192.1.1.x, and example subnet mask 
   255.255.255.240.
 
   We first define the domain for the class C net,
 
$origin  1.1.192.in-addr.arpa
@       SOA   (usual stuff)
@       ns  some.nameserver
        ns  some.other.nameserver
; delegate a subdomain
one     ns  one.nameserver
        ns  some.nameserver
; delegate another
two     ns  two.nameserver
        ns  some.nameserver
; CNAME pointers to subdomain one
0       CNAME 0.one
1       CNAME 1.one
;    through
15      CNAME 15.one
; CNAME pointers to subdomain two
16      CNAME 16.two
17      CNAME 17.two
31      CNAME 31.two
; CNAME as many as required.
 
 
   Now, in the delegated nameserver, one.nameserver
 
$origin one.1.1.192.in-addr.arpa
@       SOA (usual stuff)
        NS  one.nameserver
        NS  some.nameserver   ;  secondary for us
0       PTR  onenet.one.domain
1       PTR  onehost.one.domain
;   through
15      PTR  lasthost.one.domain

   And similar for the two.1.1.192.in-addr.arpa delegated domain.
 
 
------------------------------

Date: Sun Nov 27 23:32:41 EST 1994
Subject: Q4.4 - Recommended format/style of DNS files

Q:  Are there any suggestions for how to layout DNS configuration files
    (both forward and reverse)?
 
A: This answer is quoted from an article posted by Paul Vixie:
 
   I've gone back and forth on the question of whether the BOG should
   include a section on this topic.  I know what I myself prefer, but
   I'm wary of ramming my own stylistic preferences down the throat of
   every BOG reader.  But since you ask :-)...
 
   Create /var/named.  If your system is too old to have a /var, either
   create one or use /usr/local/adm/named instead.  Put your named.boot
   in it, and make /etc/named.boot a symlink to it.  If your system
   doesn't have symlinks, you're S-O-L (but you knew that).  In
   named.boot, put a "directory" directive that specifies your actual
   BIND working directory:
 
        directory       /var/named
 
   All relative pathnames used in "primary", "secondary", and "cache"
   directives will be evaluated relative to this directory.  Create two
   subdirectories, /var/named/pri and /var/named/sec.  Whenever you add
   a "primary" directive to your named.boot, use "pri/WHATEVER" as the
   path name.  And then put the primary zone file into "pri/WHATEVER".
   Likewise when you add "secondary" directives, use "sec/WHATEVER" and
   BIND (really named-xfer) will create the files in that
   subdirectory.
 
   (Variations: (1) make a midlevel directory "zones" and put "pri" and
   "sec" into it; (2) if you tend to pick up a lot of secondaries from
   a few hosts, group them together in their own subdirectories --
   something like /var/named/zones/uucp if you're a UUCP Project name
   server.)
 
   For your forward files, name them after the zone.  dec.com becomes
   "/var/named/zones/pri/dec.com".  For your reverse files, name them
   after the network number.  0.1.16.in-addr.arpa becomes
   "/var/named/zones/pri/16.1.0".

   When creating or maintaining primary zone files, try to use the same
   SOA values everywhere, except for the serial number which varies per
   zone.  Put a $ORIGIN directive at the top of the primary zone file,
   not because its needed (it's not since the default origin is the
   zone named in the "primary" directive) but because it make it easier
   to remember what you're working on when you have a lot of primary
   zones.  Put some comments up there indicating contact information
   for the real owner if you're proxying.  Use RCS and put the "Id"
   in a ";" comment near the top of the zone file.
 
   The SOA and other top level information should all be listed
   together.  But don't put IN on every line, it defaults nicely.  For
   example:
 
==============
@       IN      SOA     gw.home.vix.com. postmaster.vix.com. (
                        1994082501      ; serial
                        3600    ; refresh (1 hour)
                        1800    ; retry (30 mins)
                        604800  ; expire (7 days)
                        3600 )  ; minimum (1 hour)
 
                NS      gw.home.vix.com.
                NS      ns.uu.net.
                NS      uucp-gw-1.pa.dec.com.
                NS      uucp-gw-2.pa.dec.com.
 
                MX      10 gw.home.vix.com.
                MX      20 uucp-gw-1.pa.dec.com.
                MX      20 uucp-gw-1.pa.dec.com.
==============
 
   I don't necessarily recommend those SOA values.  Not every zone is
   as volatile as the example shown.  I do recommend that serial number
   format; it's in date format with a 2-digit per-day revision number.
   This format will last us until 2147 A.D. at which point I expect a
   better solution will have been found :-).  (Note that it would last
   until 4294 A.D. except that there are some old BINDs out there that
   use a signed quantity for representing serial number interally; I
   suppose that as long as none of these are still running after 2047
   A.D., that we can use the above serial number format until 4294
   A.D., at which point a better solution will HAVE to be found.)
 
   You'll note that I use a tab stop for "IN" even though I never again
   specify it.  This leaves room for names longer than 7 bytes without
   messing up the columns.  You might also note that I've put the MX
   priority and destination in the same tab stop; this is because both
   are part of the RRdata and both are very different from MX which is
   an RRtype.  Some folks seem to prefer to group "MX" and the priority
   together in one tab stop.  While this looks neat it's very confusing
   to newcomers and for them it violates the law of least
   astonishment.
 
   If you have a multi-level zone (one which contains names that have
   dots in them), you can use additional $ORIGIN statements but I
   recommend against it since there is no "back" operator.  That is,
   given the above example you can add:
 
=============
$ORIGIN home
gw              A       192.5.5.1
=============
 
   The problem with this is that subsequent RR's had better be
   somewhere under the "home.vix.com" name or else the $ORIGIN that
   introduces them will have to use a fully qualified name.  FQDN
   $ORIGIN's aren't bad and I won't be mad if you use them.
   Unqualified ones as shown above are real trouble.  I usually stay
   away from them and just put the whole name in:
 
=============
gw.home         A       192.5.5.1
=============
 
   In your reverse zones, you're usually in some good luck because the
   owner name is usually a single short token or sometimes two.
 
=============
$ORIGIN 5.5.192.in-addr.arpa.
@       IN      SOA     ...
                NS      ...
1               PTR     gw.home.vix.com.
=========================================
$ORIGIN 1.16.in-addr.arpa.
@       IN      SOA     ...
                NS      ...
2.0             PTR     gatekeeper.dec.com.
=============

   It is usually pretty hard to keep your forward and reverse zones in
   synch.  You can avoid that whole problem by just using "h2n" (see
   the ORA book, DNS and BIND, and its sample toolkit, included in the
   BIND distribution or on ftp.uu.net (use the QUOTE SITE EXEC INDEX
   command there to find this -- I never can remember where it's at).
   "h2n" and many tools like it can just read your old /etc/hosts file
   and churn it into DNS zone files.  (May I recommend
   contrib/decwrl/mkdb.pl from the BIND distribution?)  However, if you
   (like me) prefer to edit these things by hand, you need to follow
   the simple convention of making all of your holes consistent.  If
   you use 192.5.5.1 and 192.5.5.3 but not (yet) 192.5.5.2, then in
   your forward file you will have something like
 
=============
...
gw.home         A       192.5.5.1
;avail          A       192.5.5.2
pc.home         A       192.5.5.3
=============
 
   and in your reverse file you will have something like
 
=============
...
1               PTR     gw.home.vix.com.
;2              PTR     avail
3               PTR     pc.home.vix.com.
=============
 
   This convention will allow you to keep your sanity and make fewer
   errors.  Any kind of automation (h2n, mkdb, or your own
   perl/tcl/awk/python tools) will help you maintain a consistent
   universe even if it's also a complex one.  Editing by hand doesn't
   have to be deadly but you MUST take care.
 
------------------------------
 
Date: Sun Nov 27 23:32:41 EST 1994
Subject: Q4.5 - DNS on a system not connected to the Internet

 
Q: How do I use DNS on a system that is not connected to the Internet or
   set BIND up with an internal root server ?
 
A: You need to create your own root domain name server until you connect 
   to the internet.  Your roots need to delegate to mydomain.com and any
   in-addr.arpa subdomains you might have, and that's about it.  As
   soon as you're connected, rip out the fake roots and use the real
   ones.
 
   It does not actually have to be another server pretending to be the root.
   You can set up the name server so that it is primary for each domain
   above you and leave them empty (i.e. you are foo.bar.com - claim to be
   primary for bar.com and com)
 
Q: What if you connect intermittently and want DNS to work when you are
   connected, and "fail" when you are not ?
 
A: You can point the resolver at the name server at the remote site and
   if the connection (SLIP/PPP) isn't up, the resolver doesn't have a
   route to the remote server and since there's only one name server in
   resolv.conf, the resolver quickly backs off the using /etc/hosts.
   No problem.  You could do the same with multiple name server and a
   resolver that did configurable /etc/hosts fallback.
 
------------------------------
 
Date: Fri Dec  2 15:40:49 EST 1994
Subject: Q4.6 -Multiple Domain configuration

 
Q: I have seen sites that seem to have multiple domain names pointing to the
   same destination. I would like to implement this and have found no
   information explaining how to do it. What I would like to do is:
 
      ftp ftp.biff.com connects user to -> ftp.biff.com
      ftp ftp.fred.com connects user to -> ftp.biff.com
      ftp ftp.bowser.com connects user to -> ftp.biff.com
 
A: This is done through CNAME records:
 
      ftp.bowser.com.         IN      CNAME ftp.biff.com.

    You can also do the same thing with multiple A records.
   
 
------------------------------
 
Date: Sun Nov 27 23:32:41 EST 1994
Subject: Q4.7 - wildcard MX records

Q: Does BIND not understand wildcard MX records such as the following?
 
     *.foo.com       MX      0       mail.foo.com.
 
A: Explicit RR's at one level of specificity will, by design, "block" a
   wildcard at a lesser level of specificity. I suspect that you have
   an RR (an A RR, perhaps?) for "bar.foo.com" which is blocking the
   application of your "*.foo.com" wildcard. The initial MX query is
   thus failing (NOERROR but an answer count of 0), and the backup
   query finds the A RR for "bar.foo.com" and uses it to deliver the
   mail directly (which is what you DIDN'T want it to do).  Adding an
   explicit MX RR for the host is therefore the right way to handle
   this situation.
 
   See RFC 1034, Section 4.3.3 ("Wildcards") for more information on
   this "blocking" behavior, along with an illustrative example. See
   also RFC 974 for an explanation of standard mailer behavior in the
   face of an "empty" response to one's MX query.
 
   Basically, what it boils down to is, there is no point in trying to
   use a wildcard MX for a host which is otherwise listed in the DNS.
   It just doesn't work.
 
------------------------------

Date: Thu Dec  1 11:10:39 EST 1994
Subject: Q4.8 - How to identify a wildcard MX record


Q: How do you identify a wildcard MX record ?

A: You don't really need to "identify" a wildcard MX RR.  The precedence 
   for u@dom is:
 
        exact match MX
        exact match A
        wildcard MX
 
   One way to implement this is to query for ("dom",IN,MX) and if the
   answer name that comes back is "*." something, you know it's a
   wildcard, therefore you know there is no exact match MX, and you
   therefore query for ("dom",IN,A) and if you get something, use it.
   if you don't, use the previous wildcard response.
 
   RFC 974 explains this pretty well.
 
------------------------------

Date: Sun Nov 27 23:32:41 EST 1994
Subject: Q4.9 - Why are fully qualified domain names recommended ?

 
Q: Why are fully qualified domain names recommended ?
 
A: The documentation for BIND 4.9.2 says that the hostname should be set 
   to the full domain style name (i.e host.our.domain rather than
   host).  What advantages are there in this, and are there any adverse
   consequences if we don't?
 
A: Paul Vixie likes to do it :-)  He lists a few reasons -
 
   * Sendmail can be configured to just use Dj$w rather than
     Dj$w.mumble where "mumble" is something you have to edit in by
     hand.  Granted, most people use "mumble" elsewhere in their config
     files ("tack on local domain", etc) but why should it be a
     requirement ?
 
   * The real reason is that not doing it violates a very useful invariant:
 
    gethostbyname(gethostname) == gethostbyaddr(primary_interface_address)
 
     If you take an address and go "backwards" through the PTR's with
     it, you'll get a FQDN, and if you push that back through the A
     RR's, you get the same address.  Or you should.  Many multi-homed
     hosts violate this uncaringly.

     If you take a non-FQDN hostname and push it "forwards" through the
     A RR's, you get an address which, if you push it through the
     PTR's, comes back as a FQDN which is not the same as the hostname
     you started with.  Consider the fact that, absent NIS/YP, there is
     no "domainname" command analogous to the "hostname" command.
     (NIS/YP's doesn't count, of course, since it's
     sometimes-but-only-rarely the same as the Internet domain or
     subdomain above a given host's name.)  The "domain" keyword in
     resolv.conf doesn't specify the parent domain of the current host;
     it specifies the default domain of queries initiated on the
     current host, which can be a very different thing.  (As of RFC
     1535 and BIND 4.9.2's compliance with it, most people use "search"
     in resolv.conf, which overrides "domain", anyway.)
 
     What this means is that there is NO authoritative way to
     programmatically discover your host's FQDN unless it is set in the
     hostname, or unless every application is willing to grovel the
     "netstat -in" tables, find what it hopes is the primary address,
     and do a PTR query on it.
 
     FQDN /bin/hostnames are, intuitively or not, the simplest way to go.
 
------------------------------

Date: Wed Mar  1 11:04:43 EST 1995
Subject: Q4.10 - Distributing load using named
 
Q: If you attempt to distribute the load on a system using named, won't 
   the first response be cached, and then later queries use the cached
   value? (This would be for requests that come through the same
   server.)
 
A: Yes.  So it can be useful to use a lower TTL on records where this is
   important.  You can use values like 300 or 500 seconds.

   If your local caching server has ROUND_ROBIN, it does not matter
   what the authoritative servers have -- every response from the cache
   is rotated.

   But if it doesn't, and the authoritative server site is depending on
   this feature (or the old "shuffle-A") to do load balancing, then if
   one doesn't use small TTLs, one could conceivably end up with a
   really nasty situation, e.g., hundreds of workstations at a branch
   campus pounding on the same front end at the authoritative server's
   site during class registration.

   Not nice.

A: Paul Vixie has an example of the ROUND_ROBIN code in action.  Here is 
   something that he wrote regarding his example:

     >I want users to be distributed evenly among those 3 hosts.

     Believe it or not :-), BIND offers an ugly way to do this.  I offer
     for your collective amusement the following snippet from the
     ugly.vix.com zone file:

       hydra           cname        hydra1
                       cname        hydra2
                       cname        hydra3
       hydra1          a            10.1.0.1
                       a            10.1.0.2
                       a            10.1.0.3
       hydra2          a            10.2.0.1
                       a            10.2.0.2
                       a            10.2.0.3
       hydra3          a            10.3.0.1
                       a            10.3.0.2
                       a            10.3.0.3
       
      Note that having multiple CNAME RR's at a given name is
      meaningless according to the DNS RFCs but BIND doesn't mind (in
      fact it doesn't even complain).  If you call
      gethostbyname("hydra.ugly.vix.com") (try it!) you will get
      results like the following.  Note that there are two round robin
      rotations going on: one at ("hydra",CNAME) and one at each
      ("hydra1",A) et al.  I used a layer of CNAME's above the layer of
      A's to keep the response size down.  If you don't have nine
      addresses you probably don't care and would just use a pile of
      CNAME's pointing directly at real host names.

      {hydra.ugly.vix.com}
      name: hydra2.ugly.vix.com
      aliases: hydra.ugly.vix.com
      addresses: 10.2.0.2 10.2.0.3 10.2.0.1

      {hydra.ugly.vix.com}
      name: hydra3.ugly.vix.com
      aliases: hydra.ugly.vix.com
      addresses: 10.3.0.2 10.3.0.3 10.3.0.1

      {hydra.ugly.vix.com}
      name: hydra1.ugly.vix.com
      aliases: hydra.ugly.vix.com
      addresses: 10.1.0.2 10.1.0.3 10.1.0.1

      {hydra.ugly.vix.com}
      name: hydra2.ugly.vix.com
      aliases: hydra.ugly.vix.com
      addresses: 10.2.0.3 10.2.0.1 10.2.0.2

      {hydra.ugly.vix.com}
      name: hydra3.ugly.vix.com
      aliases: hydra.ugly.vix.com
      addresses: 10.3.0.3 10.3.0.1 10.3.0.2

 
------------------------------
 
Date: Sun Dec  4 22:12:32 EST 1994
Subject: Q4.11 - Order of returned records

Q: Is there any way to tell named to return records, specifically
   address records, in the order in which they are listed in the
   database?

   It would appear that named consistently applies a sorting algorithm
   to address records which seems to be virtually guaranteed to be
   pessimal for our routers, which have many A records.

A: Sorting, is the *resolver's* responsibility.  RFC 1123:

         6.1.3.4  Multihomed Hosts

            When the host name-to-address function encounters a host
            with multiple addresses, it SHOULD rank or sort the
            addresses using knowledge of the immediately connected
            network number(s) and any other applicable performance or
            history information.

            DISCUSSION:
                 The different addresses of a multihomed host generally
                 imply different Internet paths, and some paths may be
                 preferable to others in performance, reliability, or
                 administrative restrictions.  There is no general way
                 for the domain system to determine the best path.  A
                 recommended approach is to base this decision on local
                 configuration information set by the system
                 administrator.

   In BIND 4.9.x's resolver code, the "sortlist" directive in resolv.conf 
   can be used to configure this.

------------------------------

Date: Fri Feb 10 15:46:17 EST 1995
Subject: Q4.12 - resolv.conf


Q: Why should I use "real" IP addresses in /etc/resolv.conf and not 0.0.0.0 
   or 127.0.0.1.

A: Paul Vixie writes on the issue of the contents of resolv.conf:

   It's historical.  Some kernels can't unbind a UDP socket's source
   address, and some resolver versions (notably not including BIND
   4.9.2 or 4.9.3's) try to do this.  The result can be wide area
   network traffic with 127.0.0.1 as the source address.  Rather than
   giving out a long and detailed map of version/vendor combinations of
   kernels/BINDs that have/don't this problem, I just tell folks not to
   use 127.0.0.1 at all.
 
   0.0.0.0 is just an alias for the first interface address assigned
   after a system boot, and if that interface is a up-and-down point to
   point link (PPP, SLIP, whatever), there's no guarantee that you'll
   be able to reach yourself via 0.0.0.0 during the entire lifetime of
   any system instance.  On most kernels you can finesse this by adding
   static routes to 127.0.0.1 for each of your interface addresses, but
   some kernels don't like that trick and rather than give a detailed
   map of which ones work and which ones don't, I just globally
   recommend against 0.0.0.0.
 
   If you know enough to know that 127.0.0.1 or 0.0.0.0 is safe on your
   kernel and resolver, then feel free to use them.  If you don't know
   for sure that it is safe, don't use them.  I never use them (except
   on my laptop, whose hostname is "localhost" and whose 0.0.0.0 is
   127.0.0.1 since I ifconfig my lo0 before any other interface).  The
   operational advantage to using a real IP address rather than an
   wormhole like 0.0.0.0 or 127.0.0.1, is that you can then "rdist" or
   otherwise share identical copies of your resolv.conf on all the
   systems on any given subnet, not all of which will be servers.

A: The problem was with older versions of the resolver (4.8.X).  If you
   listed 127.0.0.1 as the first entry in resolv.conf, and for whatever
   reason the local name server wasn't running and the resolver fell
   back to the second name server listed, it would send queries to the
   name server with the source IP address set to 127.0.0.1 (as it was
   set when the resolver was trying to send to 127.0.0.1--you use the
   loopback address to send to the loopback address).

------------------------------

Date: Mon Jan  2 13:50:13 EST 1995
Subject: Q4.13 - Delegating authority 

Q: How do I delegate authority for domains within my domain ?

A: When you start having a very big domain that can be broken into logical 
   and separate entities that can look after their own DNS information,
   you will probably want to do this.  Maintain a central area for the
   things that everyone needs to see and delegate the authority for the
   other parts of the organization so that they can manage themselves.
    
   Another essential piece of information is that every domain that
   exists must have it NS records associated with it.  These NS records
   denote the name servers that are queried for information about that
   zone.  For your zone to be recognized by the outside world, the
   server responsible for the zone above you must have created a NS
   record for your machine in your domain.  For example, putting the
   computer club onto the network and giving them control over their
   own part of the domain space we have the following.
   
   The machine authorative for gu.uwa.edu.au is mackerel and the machine
   authorative for ucc.gu.uwa.edu.au is marlin.
    
   in mackerel's data for gu.uwa.edu.au we have the following
    
   @               IN      SOA ...
                   IN      A       130.95.100.3
                   IN      MX      mackerel.gu.uwa.edu.au.
                   IN      MX      uniwa.uwa.edu.au.
    
   marlin          IN      A       130.95.100.4
 
   ucc             IN      NS      marlin.gu.uwa.edu.au.
                   IN      NS      mackerel.gu.uwa.edu.au.

   Marlin is also given an IP in our domain as a convenience.  If they
   blow up their name serving there is less that can go wrong because
   people can still see that machine which is a start.  You could place
   "marlin.ucc" in the first column and leave the machine totally
   inside the ucc domain as well.
 
   The second NS line is because mackerel will be acting as secondary name
   server for the ucc.gu domain.  Do not include this line if you are not
   authorative for the information included in the sub-domain.


------------------------------

Date: Wed Mar  1 11:45:00 EST 1995
Subject: Q4.14 - DNS instead of NIS on a Sun OS 4.1.x system

Q: I would appreciate any comments on whether running bind 4.9.x will 
   enable sendmail, ftp, telnet and other TCP/IP services to bypass
   NIS and connect directly to named.
 
A: How to do this is documented quite well in the comp.sys.sun.admin FAQ in
   questions one and two.  You can get them from:

      ftp://thor.ece.uc.edu/pub/sun-faq/FAQs/sun-faq.general 
      http://www.cis.ohio-state.edu/hypertext/faq/usenet/comp-sys-sun-faq

   as well as from rtfm.mit.edu in the usual place, etc.
 

------------------------------

Date: Mon Jan  2 13:49:43 EST 1995
Subject: Q5.1 - No address for root server

 
Q: I've been getting the following messages lately from bind-4.9.2..
        ns_req: no address for root server
 
We are behind a firewall and have the following for our named.cache file -
 
        ; list of servers
        .               99999999    IN  NS  POBOX.FOOBAR.COM.
                        99999999    IN  NS  FOOHOST.FOOBAR.COM.
        foobar.com.     99999999    IN  NS  pobox.foobar.com.
 
A:  You can't do that.  Your nameserver contacts POBOX.FOOBAR.COM, gets the
    correct list of root servers from it, then tries again and fails
    because of your firewall.
 
    You will need a 'forwarder' definition, to ensure that all requests
    are forwarded to a host which can penetrate the firewall.  And
    it is unwise to put phony data into 'named.cache'.
 
------------------------------

Date: Sun Nov 27 23:32:41 EST 1994
Subject: Q5.2 - Error - No Root Nameservers for Class XX

Q: I've received errors before about "No root nameservers for class XX"
   but they've been because of network connectivity problems.
   I believe that Class 1 is Internet Class data.
   And I think I heard someone say that Class 4 is Hesiod??
   Does anyone know what the various Class numbers are?

A:  From RFC 1700:

       DOMAIN NAME SYSTEM PARAMETERS
       The Internet Domain Naming System (DOMAIN) includes several
       parameters.  These are documented in [RFC1034] and [RFC1035].  The
       CLASS parameter is listed here.  The per CLASS parameters are 
       defined in separate RFCs as indicated.

       Domain System Parameters:

       Decimal   Name                                          References
       --------  ----                                          ----------
              0  Reserved                                           [PM1]
              1  Internet (IN)                              [RFC1034,PM1]
              2  Unassigned                                         [PM1]
              3  Chaos (CH)                                         [PM1]
              4  Hesoid (HS)                                       [PM1]
        5-65534  Unassigned                                         [PM1]
          65535  Reserved                                           [PM1]

DNS information for RFC 1700 was taken from

        ftp://ftp.isi.edu/in-notes/iana/assignments/dns-parameters

   Hesiod is class 4, and there are no official root nameservers for class 
   4, so you can safely declare yourself one if you like.  You might want 
   to put up a packet filter so that no one outside your network is capable 
   of making Hesiod queries of your machines, if you define yourself to be 
   a root nameserver for class 4.

------------------------------
 
Date: Sun Nov 27 23:32:41 EST 1994
Subject: Q5.3 - Bind 4.9.x and MX querying?

 
Q: If I query a 4.9.x DNS server for MX records, a list of the MX records 
   as well as a list of the authorative nameservers is returned.  Why ?
 
A: Bind 4.9.2 returns the list of nameserver that are authorative
   for a domain in the response packet, along with their IP
   addresses in the additional section.
 
------------------------------

Date: Sat Sep  9 00:36:01 EDT 1995
Subject: Q5.4 - Some root nameservers don't know localhost

Q: Do I need to define an A record for localhost ?

   Where is the A record for 127.0.0.1 defined?  I see where
   the PTR record is defined pointing to localhost, but can't find
   where the A record is.  And is the A record supposed to be
   localhost.MY_DOMAIN or just localhost ?

A: Somewhere deep in the BOG (BIND Operations Guide) that came with
   4.9.3 (section 5.4.3), it says that you define this yourself 
   (if need be) in the same zone files as your "real" IP addresses 
   for your domain.  Quoting the BOG:

                                 ... As  implied by this PTR
         record, there should be a  ``localhost.my.dom.ain''
         A  record  (with address 127.0.0.1) in every domain
         that contains hosts.  ``localhost.'' will lose  its
         trailing dot when 1.0.0.127.in-addr.arpa is queried
         for;...

   The sample files in the BIND distribution show you what needs to be
   done (see the BOG).

   Some HP boxen (especially those running HP OpenView) will also need
   "loopback" defined with this IP address.   You may set it as a CNAME 
   record pointing to the "localhost." record.

------------------------------
 
Date: Sun Nov 27 23:32:41 EST 1994
Subject: Q5.5 - MX records and CNAMES and separate A records for MX targets

Q: The O'Reilly "DNS and Bind" book warns against using non-canonical
   names in MX records, however, this warning is given in the context
   of mail hubs that MX to each other for backup purposes.  I don't see
   how this applies to mail spokes.  RFC 974 has a similar warning, but
   I can not see where it specifically prohibits using an alias in an
   MX record.
 
A: Without the restrictions in the RFC, a MTA must request the A records 
   for every MX listed to determine if it is in the MX list then reduce
   the list. This introduces many more lookups than would other wise be
   required. If you are behind a 1200 bps link YOU DON'T WANT TO DO
   THIS. The addresses associated with CNAMES are not passed as
   additional data so you will force additional traffic to result even
   if you are running a caching server locally.
 
   There is also the problem of how does the MTA find all of it's
   IP addresses. This is not straight forward. You have to be able
   to do this is you allow CNAMEs (or extra A's) as MX targets.
 
   The letter of the law is that an MX record should point to an A record.
       
   There is no "real" reason to use CNAMEs for MX targets or separate
   As for nameservers any more. CNAMEs for services other than mail
   should be used because there is no specified method for locating the
   desired server yet.
 
   People don't care what the names of MX targets are.  They're
   invisible to the process anyway.  If you have mail for "mary"
   redirected to "sue" is totally irrelevant.  Having CNAMEs as the
   targets of MX's just needlessly complicates things, and is more work
   for the resolver.
 
   Having separate A's for nameservers like "ns.your.domain" is
   pointless too, since again nobody cares what the name of your
   nameserver is, since that too is invisible to the process.  If you
   move your nameserver from "mary.your.domain" to "sue.your.domain"
   nobody need care except you and your parent domain administrator
   (and the InterNIC).  Even less so for mail servers, since only you
   are affected.

Q: Given the example - 

     hello in cname     realname
     mailx in mx        0 hello

   Now, while reading the operating manual of bind it clearly states
   that this is *not* valid.  These two statements clearly contradict
   each other.  Is there some later rfc than 974 that overrides what is
   said in there with respect to MX and CNAMEs?  Anyone have the
   reference handy?

A: This isn't what the BOG says at all.  See below.  You can have a CNAME 
   that points to some other RR type; in fact, all CNAMEs have to point
   to other names (Canonical ones, hence the C in CNAME).  What you
   can't have is an MX that points to a CNAME.  MX RR's that point to
   names which have only CNAME RR's will not work in many cases, and
   RFC 974 intimates that it's a bad idea:

      Note that the algorithm to delete irrelevant RRs breaks if LOCAL has
      a alias and the alias is listed in the MX records for REMOTE.  (E.g.
      REMOTE has an MX of ALIAS, where ALIAS has a CNAME of LOCAL).  This
      can be avoided if aliases are never used in the data section of MX
      RRs.

   Here's the relevant BOG snippet:

         aliases    {ttl}   addr-class   CNAME   Canonical name
         ucbmonet           IN           CNAME   monet

         The  Canonical  Name resource record, CNAME, speci-
         fies an alias or  nickname  for  the  official,  or
         canonical,  host  name.   This record should be the
         only one associated with the alias name.  All other
         resource  records  should  be associated  with the
         canonical  name,  not  with  the   nickname.  Any
         resource  records  that  include  a  domain name as
         their value (e.g., NS or MX) must list the  canoni-
         cal name, not the nickname.

------------------------------
 
Date: Wed Mar  1 11:14:10 EST 1995
Subject: Q5.6 - NS is a CNAME

Q: Can I do this ?  Is it legal ?

   @                       SOA     (.........)
                           NS      ns.host.this.domain.
                           NS      second.host.another.domain.
   ns                      CNAME   third
   third           IN      A       xxx.xxx.xxx.xxx


A: No.  Only one RR type is allowed to refer, in its data field, to a
   CNAME, and that's CNAME itself.  So CNAMEs can refer to CNAMEs but 
   NSs and MXs cannot.

   BIND 4.9.3 (Beta11 and later) explicitly syslogs this case rather than 
   simply failing as pre-4.9 servers did.  Here's a current example:

    Dec  7 00:52:18 gw named[17561]: \
                   "foobar.com IN NS" points to a CNAME (foobar.foobar.com)

   Here is the reason why:

      Nameservers are not required to include CNAME records in the
      Additional Info section returned after a query.  It's partly an
      implementation decision and partly a part of the spec.  The
      algorithm described in RFC 1034 (pp24,25; info also in RFC 1035,
      section 3.3.11, p 18) says 'Put whatever addresses are available
      into the additional section, using glue RRs [if necessary]'.
      Since NS records are speced to contain only primary names of
      hosts, not CNAMEs, then there's no reason for algorithm to
      mention them. If, on the other hand, it's decided to allow CNAMEs
      in NS records (and indeed in other records) then there's no
      reason that CNAME records might not be included along with A
      records.  The Additional Info section is intended for any
      information that might be useful but which isn't strictly the
      answer to the DNS query processed.  It's an implementation
      decision in as much as some servers used to follow CNAMEs in 
      NS references.


------------------------------

Date: Fri Dec  2 16:17:31 EST 1994
Subject: Q5.7 - Nameserver forgets own A record

 
Q: Lately, I've been having trouble with named 4.9.2 and 4.9.3.  
   Periodically, the nameserver will seem to "forget" its own A record,
   although the other information stays intact.  One theory I had was
   that somehow a site that the nameserver was secondary for was
   "corrupting" the A record somehow.
 
A: This is invariably due to not removing ALL of the cached zones
   when you moved to 4.9.X. Remove ALL cached zones and restart
   your nameservers.
 
   You get "ignoreds" because the primaries for the relevant zones are
   running old versions of BIND which pass out more glue than is
   required. named-xfer trims off this extra glue.
 
------------------------------

Date: Sun Dec  4 22:21:22 EST 1994
Subject: Q5.8 - General problems (core dumps !)

Q: I am running bind 4.9.3b9p1 on a DEC alpha OSF/1 V3.0 and have had it 
   core dump while in debug mode.  The last lines printed to named.run 
   were [...]

A: Paul Vixie says:

   I'm always interested in hearing about cases where BIND dumps core.
   However, I need a stack trace.   Compile with -g and not -O (unless
   you are using gcc and know what you are doing) and then when it
   dumps core, get into dbx or gdb using the executable and the core
   file and use "bt" to get a stack trace.   Send it to me
   <paul@vix.com> along with specific circumstances leading to or
   surrounding the crash (test data, tail of the debug log, tail of the
   syslog... whatever matters) and ideally you should save your core
   dump for a day or so in case I have questions you can answer via
   gdb/dbx.

------------------------------

Date: Mon Jan  2 14:19:22 EST 1995
Subject: Q5.9 - malloc and DECstations

We have replaced malloc on our DECstations with a malloc that is more 
compact in memory usage, and this helped the operation of bind a lot.
The source is now available for anonymous ftp from

   ftp://ftp.cs.wisc.edu/pub/misc/malloc.tar.gz
 

------------------------------

Date: Fri Apr 28 13:56:32 EDT 1995
Subject: Q6 - Acknowledgements

Listed in e-mail address alphabetical order, the following people have 
contributed to this FAQ:

Benoit.Grange@inria.fr (Benoit.Grange)
D.T.Shield@csc.liv.ac.uk (Dave Shield)
adam@comptech.demon.co.uk (Adam Goodfellow)
andras@is.co.za (Andras Salamon)
barmar@nic.near.net (Barry Margolin)
barr@pop.psu.edu (David Barr)
bj@herbison.com (B.J. Herbison)
bje@cbr.fidonet.org (Ben Elliston)
brad@birch.ims.disa.mil (Brad Knowles)
ckd@kei.com (Christopher Davis)
cdp@hertz.njit.edu (Chris Peckham)
cricket@hp.com (Cricket Liu)
cudep@csv.warwick.ac.uk (Ian 'Vato' Dickinson [ID17])
dparter@cs.wisc.edu (David Parter)
e07@nikhef.nl (Eric Wassenaar)
fwp@CC.MsState.Edu (Frank Peters)
gah@cco.caltech.edu (Glen A. Herrmannsfeldt) 
glenn@popco.com (Glenn Fleishman)
harvey@indyvax.iupui.edu (James Harvey)
hubert@cac.washington.edu (Steve Hubert)
jmalcolm@uunet.uu.net (Joseph Malcolm)
jhawk@panix.com (John Hawkinson)
kevin@cfc.com (Kevin Darcy)
lamont@abstractsoft.com (Sean T. Lamont)
lavondes@tidtest.total.fr (Michel Lavondes)
mark@ucsalf.ac.uk (Mark Powell)
marka@syd.dms.CSIRO.AU (Mark Andrews)
mathias@unicorn.swi.com.sg (Mathias Koerber)
mjo@iao.ford.com (Mike O'Connor)
nick@flapjack.ieunet.ie (Nick Hilliard)
patrick@oes.amdahl.com (Patrick J. Horgan)
ph10@cus.cam.ac.uk (Philip Hazel)
rv@seins.Informatik.Uni-Dortmund.DE (Ruediger Volk)
shields@tembel.org (Michael Shields)
tanner@george.arc.nasa.gov (Rob Tanner)
vixie@vix.com (Paul A Vixie)
wag@swl.msd.ray.com (William Gianopoulos {84718})
whg@inel.gov (Bill Gray)
wolf@pasteur.fr (Christophe Wolfhugel)

Thank you !