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Newsgroups: comp.protocols.tcp-ip.domains,comp.answers,news.answers Path: informatik.tu-muenchen.de!Germany.EU.net!main.Germany.EU.net!EU.net!howland.erols.net!news.sgi.com!rutgers!njitgw.njit.edu!hertz.njit.edu!cdp2582 From: cdp2582@hertz.njit.edu (Chris Peckham) Subject: comp.protocols.tcp-ip.domains Frequently Asked Questions (FAQ) (Part 2 of 2) Message-ID: <cptd-faq-2-844662719@njit.edu> Followup-To: comp.protocols.tcp-ip.domains Originator: cdp2582@hertz.njit.edu Keywords: BIND,DOMAIN,DNS Sender: news@njit.edu Supersedes: <cptd-faq-2-841897014@njit.edu> Nntp-Posting-Host: hertz.njit.edu X-Posting-Frequency: posted during the first week of each month Reply-To: domain-faq@njit.edu (comp.protocols.tcp-ip.domains FAQ comments) Organization: NJIT.EDU - New Jersey Institute of Technology, Newark, NJ, USA References: <cptd-faq-1-844662719@njit.edu> Date: Mon, 7 Oct 1996 04:32:08 GMT Approved: news-answers-request@MIT.EDU Expires: Mon 11 Nov 96 00:31:59 EDT Lines: 1352 Xref: informatik.tu-muenchen.de comp.protocols.tcp-ip.domains:14351 comp.answers:21516 news.answers:83577 Posted-By: auto-faq 3.1.1.2 Archive-name: internet/tcp-ip/domains-faq/part2 Revision: 1.11 1996/09/05 04:16:22 This FAQ is edited and maintained by Chris Peckham, <cdp@pfmc.net>. The latest version may always be found for anonymous ftp from ftp://rtfm.mit.edu/pub/usenet/news.answers/internet/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@pfmc.net ! If you know of any items that are not included and you feel that they should be, send the relevant information to domain-faq@pfmc.net. ------------------------------ Date: Wed Sep 4 23:45:28 EDT 1996 Subject: Table of Contents Table of Contents Subject: Table of Contents Table of Contents ================= Part 1 ------ 0. TO DO / UPDATES 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 IP of primary name server 1.8 Change of Domain name 1.9 How memory and CPU does DNS use ? 1.10 Other things to consider when planning your servers 1.11 Proper way to get NS and reverse IP records into DNS 1.12 How to get my address assigned from the NIC ? 1.13 Is there a block of private IP addresses I can use? 1.14 Cache failed lookups 1.15 What does an NS record really do ? 1.16 DNS ports 1.17 Obtaining the latest cache file 1.18 Selecting a nameserver/root cache 1.19 InterNIC and domain names 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 and moving 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 4.15 Patches to add functionality to BIND 4.16 How to serve multiple domains from one server 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 5.10 Can't resolve names without a "." 5.11 Err/TO errors being reported 5.12 Why does swapping kill BIND ? 6. ACKNOWLEDGEMENTS ------------------------------ Date: Fri Jul 5 23:54:35 EDT 1996 Subject: Q4.1 - Changing a Secondary server to a Primary and moving 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. Q: How do I move my primary nameserver from one server to another ? A: The usual solution is to move the primary to ns.newserver.com, and have ns.oldserver.com be configured as a secondary server until the change to the root servers takes place after the request has been made to the InterNIC. Q: I am currently moving to a diffrent ISP which will change my IP's. Now I have 26+ domains that I am Primary and Secondary name servers for. Is there a way to have a change of these domains name servers all at once on a specific day? Is there a recommened setting for the SOA that would minimize name servers using the old settings? A: Yes. Gradually lower the TTL value in your SOA (that's the last one of the five numbers) to always be equal to the time left until you change over. (assuming that none of your resource records have individual TTL's set, if so, do likewise witht them.) So, the day before, lower to 43200 seconds (12 hours). Then lower every few hours to be the time remaining until the change-over. So, an hour before the change, you may just want to lower it all the way to 60 seconds or so. That way no one can cache information past the change-over. After the change, start gradually incrementing the TTL value, because you'll probably be making changes to work out problems. Once everything stabilizes, move the TTL up to whatever your normal values are. To minimize name servers from using the "old settings", you can do the same thing with the "refresh" interval in the SOA (the second number of the SOA). That will tell the secondaries to refresh every X seconds. Lower that value as you approach the changeover date. You probably don't want to go much below an hour or you'll start the primary thrashing as all the secondaries perpetually refresh. ------------------------------- 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: Mon Aug 5 23:00:16 EDT 1996 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: See the Internet Draft draft-ietf-cidrd-classless-inaddr-01.txt for more information. This file is available for anonymous ftp at ftp://ds.internic.net/internet-drafts or other IETF mirror sites (ftp.is.ca.za [Africa], nic.nordu.net [Europe], munnari.oz.au [Pacific Rim], ds.internic.net [US East Coast], or ftp.isi.edu [US West Coast]). Details follow- 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. There is additional documentation and a perl script that may be used for this purpose available for anonymous ftp from: ftp://ftp.vix.com/pub/bind/gencidrzone . ------------------------------ 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: Sun May 5 23:10:41 EDT 1996 Subject: Q4.15 - Patches to add functionality to BIND There are others, but these are listed here: Q: When using the round robin DNS and assigning 3 IPs to a host (for example), anybody know of software or processes to guarantee that all 3 IPs are reachable? A: Look at http://www-leland.stanford.edu/~schemers/docs/lbnamed/lbnamed.html for precisely what you need. Q: Does anyone know where to find patches for BIND 4.9.3-P1 to support the IPv6 AAAA record format? A: The patches for 4.9.3-REL are at ftp://ftp.inria.fr/network/ipv6/ These patches will apply fairly cleanly for 4.9.3-P1. Q: How do I turn off forwarding of information from my server ? A: The patch for 4.9.3-REL may be found at ftp://ftp.vix.com/pub/bind/release/4.9.3/contrib/noforward.tar.gz. ------------------------------ Date: Wed Sep 4 23:46:35 EDT 1996 Subject: Q4.16 - How to serve multiple domains from one server Q: How do you serve more than one domain from a single server ? A: Most name server implementations allow information about multiple domains to be kept on one server, and questions about those domains to be answered by that one server. For instance, there are many large servers on the Internet that each serve information about more than 1000 different domains. To be completely accurate, a server contains information about zones, which are parts of domains that are kept as a single unit. [Ed note: for a definition of zones and domains, see Section 2: The Name Service in the "Name Server Operations Guide" included with the BIND 4.9.4 distribution.] In the configuration of the name server, the additional zones need to be specified. An important consideration is whether a particular server is primary or secondary for any specific zone--a secondary server maintains only a copy of the zone, periodically refreshing its copy from another, specified, server. In BIND, to set up a server as a secondary server for the x.y.z zone, to the configuration file /etc/named.boot add the line secondary x.y.z 10.0.0.1 db.x.y.z where 10.0.0.1 is the IP address of the server that the zone will be copied from, and db.x.y.z is a local filename that will contain the copy of the zone. ------------------------------ 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: Sun May 5 23:46:32 EDT 1996 Subject: Q5.10 - Can't resolve names without a "." Q: I am trying to debug a problem. I can not resolve fully qualified domain names unless I put a . at the end of the name. Any thoughts? A: (Answer written by Mark Andrews) You are not using a RFC1535 aware resolver. Depending upon the age of your resolver you could try adding a search directive to resolv.conf. e.g. domain <domain> search <domain> [<domain2> ...] If that doesn't work you can configure you server to serve the parent and grandparent domains as this is the default search list. "domain langley.af.mil" has an implicit "search langley.af.mil af.mil mil" in the old resolvers, and you are timing out trying to resolve the address with one of these domains tacked on. When resolving internic.net the following will be tried in order. internic.net.langley.af.mil internic.net.af.mil internic.net.mil internic.net. RFC1535 aware resolvers try qualified address first. internic.net. internic.net.langley.af.mil internic.net.af.mil internic.net.mil RFC1535 documents the problems associated with the old search algorithim, including security issues, and how to alleviate some of the problems. ------------------------------ Date: Sun May 5 23:46:32 EDT 1996 Subject: Q5.11 - Err/TO errors being reported Q: I am running the latest verison of named (4.9.3 + P1). Why are we seeing messages like: Apr 2 20:41:58 nameserver named[25846]: Err/TO getting serial# for "foobar.domain1.com" Apr 2 20:41:59 nameserver named[25846]: Err/TO getting serial# for "foobar.domain2.com" A: These generally indicate that there is one of the following problems: 1. A network problem between you and the primary, 2. A bad IP address in named.boot, 3. The primary is Lame for the zone. An external check to see if you can retrieve the SOA is the best way to work out which it is. ------------------------------ Date: Thu Jul 4 23:20:20 EDT 1996 Subject: Q5.12 - Why does swapping kill BIND ? Q: I've been diagnosing a problem with BIND 4.9.x (where x is usually 3BETA9 or 3REL) for several months now. I finally tracked it down to swap space utilization on the unix boxes. This happens under (at least) under Linux 1.2.9 & 1.2.13, SunOS 4.1.3U1, 4.1.1, and Solaris 2.5. The symptom is that if these machines get into swap at all bind quits resolving most, if not all queries. Mind you that these machines are not "swapping hard", but rather we're talking about a several hundred K TEMPORARY deficiency. I have noticed while digging through various archives that there is some referral to "bind thrashing itself to death". Is this what is happening ? A: Yes it is. Bind can't tolerate having even a few pages swapped out. The time required to send responses climbs to several seconds/request, and the request queue fills and overflows. It's possible to shrink memory consumption a lot by undefining STATS and XSTATS, and recompiling. You could nuke DEBUG too, which will cut the code size down some, but probably not the data size. If that doesn't do the job then it sounds like you'll need to move DNS onto a separate box. BIND tends to touch all of its resident pages all of the time with normal activity... if you look at the RSS verses the total process size, you will always see the RSS within, usually, 90% of the total size of the process. This means that *any* paging of named-owned pages will stall named. Thus, a machine running a heavily accessed named process cannot afford to swap *at all*. (Paul Vixie continues on this subject): I plan to try to get BIND to exhibit slightly better locality of reference in some future release. Of course, I can only do this if the query names also exhibit some kind of hot spots. If someone queries all your names often, BIND will have to touch all of its VM pool that often. (Right now, BIND touches everything pretty often even if you're just hammering on some hot spots -- that's the part I'd like to fix. Malloc isn't cooperating.) ------------------------------ Date: Thu Jul 4 23:29:40 EDT 1996 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) Todd.Aven@BankersTrust.Com 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) cdp2582@hertz.njit.edu (Chris Peckham) cricket@hp.com (Cricket Liu) cudep@csv.warwick.ac.uk (Ian 'Vato' Dickinson [ID17]) dillon@best.com (Matthew Dillon) dparter@cs.wisc.edu (David Parter) e07@nikhef.nl (Eric Wassenaar) fitz@think.com (Tom Fitzgerald) 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) ivanl@pacific.net.sg (Ivan Leong) 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) oppedahl@popserver.panix.com (Carl Oppedahl) patrick@oes.amdahl.com (Patrick J. Horgan) paul@software.com (Paul Wren) pb@fasterix.frmug.fr.net (Pierre Beyssac) ph10@cus.cam.ac.uk (Philip Hazel) phil@netpart.com (Phil Trubey) 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 !