Friday, October 29, 2010
Bassic Setting DNS Domain Server
1:54 PM | 
Posted by
bospetro
The Domain Name System is the software that lets you have name to number mappings on your computers. The name decel.ecel.uwa.edu.au is the number 130.95.4.2 and vice versa. This is achieved through the DNS. The DNS is a heirarchy. There are a small number of root domain name servers that are responsible for tracking the top level domains and who is under them. The root domain servers between them know about all the people who have name servers that are authoritive for domains under the root.
Being authoritive means that if a server is asked about something in that domain, it can say with no ambiguity whether or not a given piece of information is true. For example. We have domains x.z and y.z. There are by definition authoritive name servers for both of these domains and we shall assume that the name server in both of these cases is a machine called nic.x.z and nic.y.z but that really makes no difference.
If someone asks nic.x.z whether there is a machine called a.x.z, then nic.x.z can authoritively say, yes or no because it is the authoritive name server for that domain. If someone asks nic.x.z whether there is a machine called a.y.z then nic.x.z asks nic.y.z whether such a machine exists (and caches this for future requests). It asks nic.y.z because nic.y.z is the authoritive name server for the domain y.z. The information about authoritive name servers is stored in the DNS itself and as long as you have a pointer to a name server who is more knowledgable than yourself then you are set.
When a change is made, it propogates slowly out through the internet to eventually reach all machines. The following was supplied by Mark Andrews Mark.Andrews@syd.dms.csiro.au.
If both the primary and all secondaries are up and talking when a zone update occurs and for the refresh period after the update the old data will live for max(refresh + mininum) average (refresh/2 +mininum) for the zone. New information will be available from all servers after refresh.
So with a refresh of 3 hours and a minimum of a day, you can expect everything to be working a day after it is changed. If you have a longer minimum, it may take a couple of days before things return to normal.
There is also a difference between a zone and a domain. The domain is the entire set of machines that are contained within an organisational domain name. For example, the domain uwa.edu.au contains all the machines at the University of Western Australia. A Zone is the area of the DNS for which a server is responsible. The University of Western Australia is a large organisation and trying to track all changes to machines at a central location would be difficult. The authoritive name server for the zone uwa.edu.au delegates the authority for the zone ecel.uwa.edu.au to decel.ecel.uwa.edu.au. Machine foo.ecel.uwa.edu.au is in the zone that decel is authoritive for. Machine bar.uwa.edu.au is in the zone that uniwa.uwa.edu.au is authoritive for.
2 Installing the DNS:
First I'll assume you already have a copy of the Domain Name Server software. It is probably called named or in.named depending on your flavour of unix. I never had to get a copy, but if anyone thinks that information should be here then by all means tell me and I'll put it in. If you intend on using the package called BIND, then you should be sure that you get version 4.9.x, which is the most recent version at this point in time.
For more information on the latest version of BIND you should take a look at Internet Software Consortium which sponsors the development of BIND. - Kavli
2.1 The Boot File:
First step is to create the file named.boot. This describes to named (we'll dispense with the in.named. Take them to be the same) where the information that it requires can be found. This file is normally found in /etc/named.boot and I personally tend to leave it there because then I know where to find it. If you don't want to leave it there but place it in a directory with the rest of your named files, then there is usually an option on named to specify the location of the boot file.
An alternative is of course to make a symbolic link from /etc/named.boot to the wanted directory. - Kavli
Your typical boot file will look like this if you are an unimportant leaf node and there are other name servers at your site.
directory /etc/namedfiles
cache . root.cache
primary ecel.uwa.edu.au ecel.uwa.domain
primary 0.0.127.in-addr.arpa 0.0.127.domain
primary 4.95.130.in-addr.arpa 4.95.130.domain
forwarders 130.95.128.1
Here is an alternative layout used by Christophe Wolfhugel <Christophe.Wolfhugel@grasp.insa-lyon.fr> He finds this easier because of the large number of domains he has. The structure is essentially the same, but the file names use the domain name rather than the IP subnet to describe the contents.
directory /usr/local/etc/bind
cache . p/root
forwarders 134.214.100.1 192.93.2.4
;
; Primary servers
;
primary fr.net p/fr.net
primary frmug.fr.net p/frmug.fr.net
primary 127.in-addr.arpa p/127
;
; Secondary servers
;
secondary ensta.fr 147.250.1.1 s/ensta.fr
secondary gatelink.fr.net 134.214.100.1 s/gatelink.fr.net
secondary insa-lyon.fr 134.214.100.1 s/insa-lyon.fr
secondary loesje.org 145.18.226.21 s/loesje.org
secondary nl.loesje.org 145.18.226.21 s/nl.loesje.org
secondary pcl.ac.uk 161.74.160.5 s/pcl.ac.uk
secondary univ-lyon1.fr 134.214.100.1 s/univ-lyon1.fr
secondary wmin.ac.uk 161.74.160.5 s/wmin.ac.uk
secondary westminster.ac.uk 161.74.160.5 s/westminster.ac.uk
;
;
; Secondary for addresses
;
secondary 74.161.in-addr.arpa 161.74.160.5 s/161.74
secondary 214.134.in-addr.arpa 134.214.100.1 s/134.214
secondary 250.147.in-addr.arpa 147.250.1.1 s/147.250
;
; Classes C
;
secondary 56.44.192.in-addr.arpa 147.250.1.1 s/192.44.56
secondary 57.44.192.in-addr.arpa 147.250.1.1 s/192.44.57
The lines in the named.boot file have the following meanings.
directory
This is the path that named will place in front of all file names referenced from here on. If no directory is specified, it looks for files relative to /etc.
cache
This is the information that named uses to get started. Named must know the IP number of some other name servers at least to get started. Information in the cache is treated differently depending on your version of named. Some versions of named use the information included in the cache permenantly and others retain but ignore the cache information once up and running.
Be sure you get an up-to-date cache-file. An obsolete cache file is a good source of problems. - Kavli
primary
This is one of the domains for which this machine is authorative for. You put the entire domain name in. You need forwards and reverse lookups. The first value is the domain to append to every name included in that file. (There are some exceptions, but they will be explained later) The name at the end of the line is the name of the file (relative to /etc of the directory if you specified one). The filename can have slashes in it to refer to subdirectories so if you have a lot of domains you may want to split it up.
BE VERY CAREFUL TO PUT THE NUMBERS BACK TO FRONT FOR THE REVERSE LOOK UP FILE. The example given above is for the subnet ecel.uwa.edu.au whose IP address is 130.95.4.*. The reverse name must be 4.95.130.in-addr.arpa. It must be backwards and it must end with .in-addr.arpa. If your reverse name lookups don't work, check this. If they still don't work, check this again.
forwarders
This is a list of IP numbers for forward requests for sites about which we are unsure. A good choice here is the name server which is authoritive for the zone above you.
secondary (This line is not in the example, but is worth mentioning.)
A secondary line indicates that you wish to be a secondary name server for this domain. You do not need to do this usually. All it does is help make the DNS more robust. You should have at least one secondary server for your site, but you do not need to be a secondary server for anyone else. You can by all means, but you don't need to be. If you want to be a secondary server for another domain, then place the line
secondary gu.uwa.edu.au 130.95.100.3 130.95.128.1 sec/gu.uwa.edu.au
in your named.boot. This will make your named try the servers on both of the machines specified to see if it can obtain the information about those domains. You can specify a number of IP addresses for the machines to query that probably depends on your machine. Your copy of named will upon startup go and query all the information it can get about the domain in question and remember it and act as though it were authoritive for that domain.
Next you will want to start creating the data files that contain the name definitions.
2.2 The cache file:
You should always use the latest cache file. The simplest way to do this is by using dig(1) this way:
dig @ns.internic.net . ns > root.cache
You can also get a copy of the cache file by ftp'ing FTP.RS.INTERNIC.NET.
An example of a cache file is located in Appendix A.
2.3 The Forward Mapping file:
The file ecel.uwa.edu.au. will be used for the example with a couple of machines left in for the purpose of the exercise. Here is a copy of what the file looks like with explanations following.
; Authoritative data for ecel.uwa.edu.au
;
@ IN SOA decel.ecel.uwa.edu.au. postmaster.ecel.uwa.edu.au. (
93071200 ; Serial (yymmddxx)
10800 ; Refresh 3 hours
3600 ; Retry 1 hour
3600000 ; Expire 1000 hours
86400 ) ; Minimum 24 hours
IN A 130.95.4.2
IN MX 100 decel
IN MX 150 uniwa.uwa.edu.au.
IN MX 200 relay1.uu.net.
IN MX 200 relay2.uu.net.
localhost IN A 127.0.0.1
decel IN A 130.95.4.2
IN HINFO SUN4/110 UNIX
IN MX 100 decel
IN MX 150 uniwa.uwa.edu.au.
IN MX 200 relay1.uu.net
IN MX 200 relay2.uu.net
gopher IN CNAME decel.ecel.uwa.edu.au.
accfin IN A 130.95.4.3
IN HINFO SUN4/110 UNIX
IN MX 100 decel
IN MX 150 uniwa.uwa.edu.au.
IN MX 200 relay1.uu.net
IN MX 200 relay2.uu.net
chris-mac IN A 130.95.4.5
IN HINFO MAC-II MACOS
The comment character is ';' so the first two lines are just comments indicating the contents of the file.
All values from here on have IN in them. This indicates that the value is an InterNet record. There are a couple of other types, but all you need concern yourself with is internet ones.
The IN type is default and can safely be omitted. It looks better without them I think.
- Kavli
The SOA record is the Start Of Authority record. It contains the information that other nameservers will learn about this domain and how to treat the information they are given about it. The '@' as the first character in the line indicates that you wish to define things about the domain for which this file is responsible. The domain name is found in the named.boot file in the corresponding line to this filename. All information listed refers to the most recent machine/domain name so all records from the '@' until 'localhost' refer to the '@'. The SOA record has 5 magic numbers. First magic number is the serial number. If you change the file, change the serial number. If you don't, no other name servers will update their information. The old information will sit around for a very long time.
Refresh is the time between refreshing information about the SOA. Retry is the frequency of retrying if an authorative server cannot be contacted. Expire is how long a secondary name server will keep information about a zone without successfully updating it or confirming that the data is up to date. This is to help the information withstand fairly lengthy downtimes of machines or connections in the network without having to recollect all the information. Minimum is the default time to live value handed out by a nameserver for all records in a zone without an explicit TTL value. This is how long the data will live after being handed out. The two pieces of information before the 5 magic numbers are the machine that is considered the origin of all of this information. Generally the machine that is running your named is a good one for here. The second is an email address for someone who can fix any problems that may occur with the DNS. Good ones here are postmaster, hostmaster or root. NOTE: You use dots and not '@' for the email address.
eg: root.decel.ecel.uwa.edu.au is correct
and
root@decel.ecel.uwa.edu.au is incorrect.
If your name contains a dot: E.g. Ronny.Kavli@mailhost.somedomain.there. - you must escape the dot -> Ronny\.Kavli.mailhost.somedomain.there. - But, if possible, you should create a mailalias instead. That way, related mail can go to more than one person. - Kavli
We now have an address to map ecel.uwa.edu.au to. The address is 130.95.4.2 which happens to be decel, our main machine. If you try to find an IP number for the domain ecel.uwa.edu.au it will get you the machine decel.ecel.uwa.edu.au's IP number. This is a nicety which means that people who have non-MX record mailers can still mail fred@ecel.uwa.edu.au and don't have to find the name of a machine name under the domain to mail.
Now we have a couple of MX records for the domain itself. The MX records specify where to send mail destined for the machine/domain that the MX record is for. In this case we would prefer if all mail for fred@ecel.uwa.edu.au is sent to decel.ecel.uwa.edu.au. If that does not work, we would like it to go to uniwa.uwa.edu.au because there are a number of machines that might have no idea how to get to us, but may be able to get to uniwa. And failing that, try the site relay1.uu.net. A small number indicates that this site should be tried first. The larger the number the further down the list of sites to try the site is. NOTE: Not all machines have mailers that pay attention to MX records. Some only pay attention to IP numbers, which is really stupid. All machines are required to have MX-capable Mail Transfer Agents (MTA) as there are many addresses that can only be reached via this means.
Do not point an MX record to a CNAME record. A lot of mailers don't handle this. Add another A-record to it instead, but let the reverse table point to the real name. In other words: Don't add a PTR record to it. - Kavli
There is an entry for localhost now. Note that this is somewhat of a kludge and should probably be handled far more elegantly. By placing localhost here, a machine comes into existance called localhost.ecel.uwa.edu.au. If you finger it, or telnet to it, you get your own machine, because the name lookup returns 127.0.0.1 which is the special case for your own machine. I have used a couple of different DNS packages. The old BSD one let you put things into the cache which would always work, but would not be exported to other nameservers. In the newer Sun one, they are left in the cache and are mostly ignored once named is up and running. This isn't a bad solution, its just not a good one.
Decel is the main machine in our domain. It has the IP number 130.95.4.2 and that is what this next line shows. It also has a HINFO entry. HINFO is Host Info which is meant to be some sort of an indication of what the machine is and what it runs. The values are two white space seperated values. First being the hardware and second being the software. HINFO is not compulsory, its just nice to have sometimes. We also have some MX records so that mail destined for decel has some other avenues before it bounces back to the sender if undeliverable.
It is a good idea to give all machines capable of handling mail an MX record because this can be cached on remote machines and will help to reduce the load on the network.
gopher.ecel.uwa.edu.au is the gopher server in our division. Now because we are cheapskates and don't want to go and splurge on a seperate machine just for handling gopher requests we have made it a CNAME to our main machine. While it may seem pointless it does have one main advantage. When we discover that our placing terrabytes of popular quicktime movies on our gopher server (no we haven't and we don't intend to) causes an unbearable load on our main machine, we can quickly move the CNAME to point at a new machine by changing the name mentioned in the CNAME. Then the slime of the world can continue to get their essential movies with a minimal interuption to the network. Other good CNAMEs to maintain are things like ftp, mailhost, netfind, archie, whois, and even dns (though the most obvious use for this fails). It also makes it easier for people to find these services in your domain.
Regarding CNAME from dns: NS records must point to A records. Same for MX records. - Kavli
We should probably start using WKS records for things like gopher and whois rather than making DNS names for them. The tools are not in wide circulation for this to work though. (Plus all those comments in many DNS implementation of "Not implemented" next to the WKS record)
WKS == Well Known Services. - The different services a host is providing
- Kavli
Finally we have a macintosh which belongs to my boss. All it needs is an IP number, and we have included the HINFO so that you can see that it is in fact a macII running a Mac System. To get the list of preferred values, you should get a copy of RFC 1340. It lists lots of useful information such as /etc/services values, ethernet manufacturer hardware addresses, HINFO defualts and many others. I will include the list as it stands at the moment, but if any RFC superceeds 1340, then it will have a more complete list. See Appendix B for that list.
NOTE: If Chris had a very high profile and wanted his mac to appear like a fully connected unix machine as far as internet services were concerned, he could simply place an MX record such as
IN MX 100 decel
after his machine and any mail sent to chris@chris-mac.ecel.uwa.edu.au would be automatically rerouted to decel.
2.4 The Reverse Mapping File
The reverse name lookup is handled in a most bizarre fashion. Well it all makes sense, but it is not immediately obvious.
All of the reverse name lookups are done by finding the PTR record associated with the name w.x.y.z.in-addr.arpa. So to find the name associated with the IP number 1.2.3.4, we look for information stored in the DNS under the name 4.3.2.1.in-addr.arpa. They are organised this way so that when you are allocated a B class subnet for example, you get all of the IP numbers in the domain 130.95. Now to turn that into a reverse name lookup domain, you have to invert the numbers or your registered domains will be spread all over the place. It is a mess and you need not understand the finer points of it all. All you need to know is that you put the reverse name lookup files back to front.
Here is the sample reverse name lookup files to go with our example.
0.0.127.in-addr.arpa
--
; Reverse mapping of domain names 0.0.127.in-addr.arpa
; Nobody pays attention to this, it is only so 127.0.0.1 -> localhost.
@ IN SOA decel.ecel.uwa.edu.au. postmaster.ecel.uwa.edu.au. (
91061801 ; Serial (yymmddxx)
10800 ; Refresh 3 hours
3600 ; Retry 1 hour
3600000 ; Expire 1000 hours
86400 ) ; Minimum 24 hours
;
1 IN PTR localhost.ecel.uwa.edu.au.
--
4.95.130.in-addr.arpa
--
; reverse mapping of domain names 4.95.130.in-addr.arpa
;
@ IN SOA decel.ecel.uwa.edu.au. postmaster.ecel.uwa.edu.au. (
92050300 ; Serial (yymmddxx format)
10800 ; Refresh 3hHours
3600 ; Retry 1 hour
3600000 ; Expire 1000 hours
86400 ) ; Minimum 24 hours
2 IN PTR decel.ecel.uwa.edu.au.
3 IN PTR accfin.ecel.uwa.edu.au.
5 IN PTR chris-mac.ecel.uwa.edu.au.
--
It is important to remember that you must have a second start of authority record for the reverse name lookups. Each reverse name lookup file must have its own SOA record. The reverse name lookup on the 127 domain is debatable seeing as there is likely to be only one number in the file and it is blatantly obvious what it is going to map to.
In general: Each primary file pointed to in named.boot should have one - and only one - SOA record.
- Kavli
The SOA details are the same as in the forward mapping.
Each of the numbers listed down the left hand side indicates that the line contains information for that number of the subnet. Each of the subnets must be the more significant digits. eg the 130.95.4 of an IP number 130.95.4.2 is implicit for all numbers mentioned in the file.
The PTR must point to a machine that can be found in the DNS. If the name is not in the DNS, some versions of named just bomb out at this point.
Reverse name lookups are not compulsory, but nice to have. It means that when people log into machines, they get names indicating where they are logged in from. It makes it easier for you to spot things that are wrong and it is far less cryptic than having lots of numbers everywhere. Also if you do not have a name for your machine, some brain dead protocols such as talk will not allow you to connect.
Since I had this I had one suggestion of an alternative way to do the localhost entry. I think it is a matter of personal opinion so I'll include it here in case anyone things that this is a more appropriate method.
The following is courtesy of jep@convex.nl (JEP de Bie)
The way I did it was:
1) add in /etc/named.boot:
primary . localhost primary 127.in-addr.ARPA. IP127
(Craig: It has been suggested by Mark Andrews that this is a bad practice particularly if you have upgraded to Bind 4.9. You also run the risk of polluting the root name servers. This comes down to a battle of idealogy and practicality. Think twice before declaring yourself authorative for the root domain.)
So I not only declare myself (falsely? - probably, but nobody is going to listen anyway most likely [CPR]:-) athorative in the 127.in-addr.ARPA domain but also in the . (root) domain.
2) the file localhost has:
$ORIGIN .
localhost IN A 127.0.0.1
3) and the file IP127:
$ORIGIN 127.in-addr.ARPA.
1.0.0 IN PTR localhost.
4) and I have in my own domain file (convex.nl) the line:
$ORIGIN convex.nl.
localhost IN CNAME localhost.
The advantage (elegancy?) is that a query (A) of localhost. gives the reverse of the query of 1.0.0.127.in-addr.ARPA. And it also shows that localhost.convex.nl is only a nickname to something more absolute. (While the notion of localhost is of course relative :-)).
And I also think there is a subtle difference between the lines
primary 127.in-addr.ARPA. IP127
and
primary 0.0.127.in-addr.ARPA. 4.95.130.domain
=============
JEP de Bie
jep@convex.nl
=============
3 Delegating authority for domains within your domain
When you start having a very big domain that can be broken into logical and seperate 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 organisation so that they can manage themselves.
Another essential piece of information is that every domain that exists must have its 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 recognised 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.
4 Troubleshooting your named:
4.1 Named doesn't work! What is wrong?
Step 1: Run nslookup and see what nameserver it tries to connect you to. If nslookup connects you to the wrong nameserver, create a /etc/resolv.conf file that points your machine at the correct nameserver. If there is no resolv.conf file, the the resolver uses the nameserver on the local machine.
Step 2: Make sure that named is actually running.
Step 3: Restart named and see if you get any error messages on the console and in also check /usr/adm/messages.
Step 4: If named is running, nslookup connects to the appropriate nameserver and nslookup can answer simple questions, but other programs such as 'ping' do not work with names, then you need to install resolv+ most likely.
4.2 Local has noticed change, but nobody else has new info
I changed my named database and my local machine has noticed, but nobody else has the new information?
Change the serial number in the SOA for any domains that you modified and restart named. Wait an hour and check again. The information propogates out. It won't change immediately.
4.3 I can see their info, but they can't see mine
My local machine knows about all the name server information, but no other sites know about me?
Find an upstream nameserver (one that has an SOA for something in your domain) and ask them to be a secondary name server for you. eg if you are ecel.uwa.edu.au, ask someone who has an SOA for the domain uwa.edu.au. Get NS records (and glue) added to your parent zone for your zone. This is called delegating. It should be done formally like this or you will get inconsistant answers out of the DNS. ALL NAMSERVERS FOR YOUR ZONE SHOULD BE LISTED IN THIS MANNER.
4.4 Forward domain works, but not backwards
My forward domain names work, but the backward names do not?
Make sure the numbers are back to front and have the in-addr.arpa on the end.
Make sure your reverse zone is registered. For Class C nets this can be done by mailing to hostmaster@internic.net. For class A & B nets make sure that you are registeres with the primary for your net and that the net itself is registered with hostmaster@internic.net.
5 How to get useful information from nslookup:
Nslookup is a very useful program but I'm sure there are less than 20 people worldwide who know how to use it to its full usefulness. I'm most certainly not one of them. If you don't like using nslookup, there is at least one other program called dig, that has most/all(?) of the functionality of nslookup and is a hell of a lot easier to use.
I won't go into dig much here except to say that it is a lot easier to get this information out of. I won't bother because nslookup ships with almost all machines that come with network software.
To run nslookup, you usually just type nslookup. It will tell you the server it connects to. You can specify a different server if you want. This is useful when you want to tell if your named information is consistent with other servers.
5.1 Getting name to number mappings
Type the name of the machine. Typing 'decel' is enough if the machine is local.
(Once you have run nslookup successfully)
> decel
Server: ecel.uwa.edu.au
Address: 130.95.4.2
Name: decel.ecel.uwa.edu.au
Address: 130.95.4.2
>
One curious quirk of some name resolvers is that if you type a machine name, they will try a number of permutations. For example if my machine is in the domain ecel.uwa.edu.au and I try to find a machine called fred, the resolver will try the following.
fred.ecel.uwa.edu.au.
fred.uwa.edu.au.
fred.edu.au.
fred.au.
fred.
This can be useful, but more often than not, you would simply prefer a good way to make aliases for machines that are commonly referenced. If you are running resolv+, you should just be able to put common machines into the host file.
DIG: dig <machine name>
5.2 Getting number to name mappings
Nslookup defaults to finding you the Address of the name specified. For reverse lookups you already have the address and you want to find the name that goes with it. If you read and understood the bit above where it describes how to create the number to name mapping file, you would guess that you need to find the PTR record instead of the A record. So you do the following.
> set type=ptr
> 2.4.95.130.in-addr.arpa
Server: decel.ecel.uwa.edu.au
Address: 130.95.4.2
2.4.95.130.in-addr.arpa host name = decel.ecel.uwa.edu.au
>
nslookup tells you that the ptr for the machine name 2.4.95.130.in-addr.arpa points to the host decel.ecel.uwa.edu.au.
DIG: dig -x <machine number>
5.3 Finding where mail goes when a machine has no IP number
When a machine is not IP connected, it needs to specify to the world, where to send the mail so that it can dial up and collect it every now and then. This is accomplished by setting up an MX record for the site and not giving it an IP number. To get the information out of nslookup as to where the mail goes, do the following.
> set type=mx
> dialix.oz.au
Server: decel.ecel.uwa.oz.au
Address: 130.95.4.2
Non-authoritative answer:
dialix.oz.au preference = 100, mail exchanger = uniwa.uwa.OZ.AU
dialix.oz.au preference = 200, mail exchanger = munnari.OZ.AU
Authoritative answers can be found from:
uniwa.uwa.OZ.AU inet address = 130.95.128.1
munnari.OZ.AU inet address = 128.250.1.21
munnari.OZ.AU inet address = 192.43.207.1
mulga.cs.mu.OZ.AU inet address = 128.250.35.21
mulga.cs.mu.OZ.AU inet address = 192.43.207.2
dmssyd.syd.dms.CSIRO.AU inet address = 130.155.16.1
ns.UU.NET inet address = 137.39.1.3
You tell nslookup that you want to search for mx records and then you give it the name of the machine. It tells you the preference for the mail (small means more preferable), and who the mail should be sent to. It also includes sites that are authorative (have this name in their named database files) for this MX record. There are multiple sites as a backup. As can be seen, our local public internet access company dialix would like all of their mail to be sent to uniwa, where they collect it from. If uniwa is not up, send it to munnari and munnari will get it to uniwa eventually.
NOTE: For historical reasons Australia used to be .oz which was changed to .oz.au to move to the ISO standard extensions upon the advent of IP. We are now moving to a more normal heirarchy which is where the .edu.au comes from. Pity, I liked having oz.
DIG: dig <zone> mx
5.4 Getting a list of machines in a domain from nslookup
Find a server that is authorative for the domain or just generally all knowing. To find a good server, find all the SOA records for a given domain. To do this, you set type=soa and enter the domain just like in the two previous examples.
Once you have a server type
> ls gu.uwa.edu.au.
[uniwa.uwa.edu.au]
Host or domain name Internet address
gu server = mackerel.gu.uwa.edu.au
gu server = uniwa.uwa.edu.au
gu 130.95.100.3
snuffle-upagus 130.95.100.131
mullet 130.95.100.2
mackerel 130.95.100.3
marlin 130.95.100.4
gugate 130.95.100.1
gugate 130.95.100.129
helpdesk 130.95.100.180
lan 130.95.100.0
big-bird 130.95.100.130
To get a list of all the machines in the domain.
If you wanted to find a list of all of the MX records for the domain, you can put a -m flag in the ls command.
> ls -m gu.uwa.edu.au.
[uniwa.uwa.edu.au]
Host or domain name Metric Host
gu 100 mackerel.gu.uwa.edu.au
gu 200 uniwa.uwa.edu.au
This only works for a limited selection of the different types.
DIG: dig axfr <zone> @<server>
6 Appendicies
6.2 Appendix B
An Excerpt from
RFC 1340 Assigned Numbers July 1992
MACHINE NAMES
These are the Official Machine Names as they appear in the Domain Name
System HINFO records and the NIC Host Table. Their use is described in
RFC-952 [53].
A machine name or CPU type may be up to 40 characters taken from the
set of uppercase letters, digits, and the two punctuation characters
hyphen and slash. It must start with a letter, and end with a letter
or digit.
ALTO DEC-1080
ALTOS-6800 DEC-1090
AMDAHL-V7 DEC-1090B
APOLLO DEC-1090T
ATARI-104ST DEC-2020T
ATT-3B1 DEC-2040
ATT-3B2 DEC-2040T
ATT-3B20 DEC-2050T
ATT-7300 DEC-2060
BBN-C/60 DEC-2060T
BURROUGHS-B/29 DEC-2065
BURROUGHS-B/4800 DEC-FALCON
BUTTERFLY DEC-KS10
C/30 DEC-VAX-11730
C/70 DORADO
CADLINC DPS8/70M
CADR ELXSI-6400
CDC-170 EVEREX-386
CDC-170/750 FOONLY-F2
CDC-173 FOONLY-F3
CELERITY-1200 FOONLY-F4
CLUB-386 GOULD
COMPAQ-386/20 GOULD-6050
COMTEN-3690 GOULD-6080
CP8040 GOULD-9050
CRAY-1 GOULD-9080
CRAY-X/MP H-316
CRAY-2 H-60/68
CTIWS-117 H-68
DANDELION H-68/80
DEC-10 H-89
DEC-1050 HONEYWELL-DPS-6
DEC-1077 HONEYWELL-DPS-8/70
HP3000 ONYX-Z8000
HP3000/64 PDP-11
IBM-158 PDP-11/3
IBM-360/67 PDP-11/23
IBM-370/3033 PDP-11/24
IBM-3081 PDP-11/34
IBM-3084QX PDP-11/40
IBM-3101 PDP-11/44
IBM-4331 PDP-11/45
IBM-4341 PDP-11/50
IBM-4361 PDP-11/70
IBM-4381 PDP-11/73
IBM-4956 PE-7/32
IBM-6152 PE-3205
IBM-PC PERQ
IBM-PC/AT PLEXUS-P/60
IBM-PC/RT PLI
IBM-PC/XT PLURIBUS
IBM-SERIES/1 PRIME-2350
IMAGEN PRIME-2450
IMAGEN-8/300 PRIME-2755
IMSAI PRIME-9655
INTEGRATED-SOLUTIONS PRIME-9755
INTEGRATED-SOLUTIONS-68K PRIME-9955II
INTEGRATED-SOLUTIONS-CREATOR PRIME-2250
INTEGRATED-SOLUTIONS-CREATOR-8 PRIME-2655
INTEL-386 PRIME-9955
INTEL-IPSC PRIME-9950
IS-1 PRIME-9650
IS-68010 PRIME-9750
LMI PRIME-2250
LSI-11 PRIME-750
LSI-11/2 PRIME-850
LSI-11/23 PRIME-550II
LSI-11/73 PYRAMID-90
M68000 PYRAMID-90MX
MAC-II PYRAMID-90X
MASSCOMP RIDGE
MC500 RIDGE-32
MC68000 RIDGE-32C
MICROPORT ROLM-1666
MICROVAX S1-MKIIA
MICROVAX-I SMI
MV/8000 SEQUENT-BALANCE-8000
NAS3-5 SIEMENS
NCR-COMTEN-3690 SILICON-GRAPHICS
NEXT/N1000-316 SILICON-GRAPHICS-IRIS
NOW SGI-IRIS-2400
SGI-IRIS-2500 SUN-3/50
SGI-IRIS-3010 SUN-3/60
SGI-IRIS-3020 SUN-3/75
SGI-IRIS-3030 SUN-3/80
SGI-IRIS-3110 SUN-3/110
SGI-IRIS-3115 SUN-3/140
SGI-IRIS-3120 SUN-3/150
SGI-IRIS-3130 SUN-3/160
SGI-IRIS-4D/20 SUN-3/180
SGI-IRIS-4D/20G SUN-3/200
SGI-IRIS-4D/25 SUN-3/260
SGI-IRIS-4D/25G SUN-3/280
SGI-IRIS-4D/25S SUN-3/470
SGI-IRIS-4D/50 SUN-3/480
SGI-IRIS-4D/50G SUN-4/60
SGI-IRIS-4D/50GT SUN-4/110
SGI-IRIS-4D/60 SUN-4/150
SGI-IRIS-4D/60G SUN-4/200
SGI-IRIS-4D/60T SUN-4/260
SGI-IRIS-4D/60GT SUN-4/280
SGI-IRIS-4D/70 SUN-4/330
SGI-IRIS-4D/70G SUN-4/370
SGI-IRIS-4D/70GT SUN-4/390
SGI-IRIS-4D/80GT SUN-50
SGI-IRIS-4D/80S SUN-100
SGI-IRIS-4D/120GTX SUN-120
SGI-IRIS-4D/120S SUN-130
SGI-IRIS-4D/210GTX SUN-150
SGI-IRIS-4D/210S SUN-170
SGI-IRIS-4D/220GTX SUN-386i/250
SGI-IRIS-4D/220S SUN-68000
SGI-IRIS-4D/240GTX SYMBOLICS-3600
SGI-IRIS-4D/240S SYMBOLICS-3670
SGI-IRIS-4D/280GTX SYMMETRIC-375
SGI-IRIS-4D/280S SYMULT
SGI-IRIS-CS/12 TANDEM-TXP
SGI-IRIS-4SERVER-8 TANDY-6000
SPERRY-DCP/10 TEK-6130
SUN TI-EXPLORER
SUN-2 TP-4000
SUN-2/50 TRS-80
SUN-2/100 UNIVAC-1100
SUN-2/120 UNIVAC-1100/60
SUN-2/130 UNIVAC-1100/62
SUN-2/140 UNIVAC-1100/63
SUN-2/150 UNIVAC-1100/64
SUN-2/160 UNIVAC-1100/70
SUN-2/170 UNIVAC-1160
UNKNOWN
VAX-11/725
VAX-11/730
VAX-11/750
VAX-11/780
VAX-11/785
VAX-11/790
VAX-11/8600
VAX-8600
WANG-PC002
WANG-VS100
WANG-VS400
WYSE-386
XEROX-1108
XEROX-8010
ZENITH-148
SYSTEM NAMES
These are the Official System Names as they appear in the Domain Name
System HINFO records and the NIC Host Table. Their use is described
in RFC-952 [53].
A system name may be up to 40 characters taken from the set of upper-
case letters, digits, and the three punctuation characters hyphen,
period, and slash. It must start with a letter, and end with a
letter or digit.
AEGIS LISP SUN OS 3.5
APOLLO LISPM SUN OS 4.0
AIX/370 LOCUS SWIFT
AIX-PS/2 MACOS TAC
BS-2000 MINOS TANDEM
CEDAR MOS TENEX
CGW MPE5 TOPS10
CHORUS MSDOS TOPS20
CHRYSALIS MULTICS TOS
CMOS MUSIC TP3010
CMS MUSIC/SP TRSDOS
COS MVS ULTRIX
CPIX MVS/SP UNIX
CTOS NEXUS UNIX-BSD
CTSS NMS UNIX-V1AT
DCN NONSTOP UNIX-V
DDNOS NOS-2 UNIX-V.1
DOMAIN NTOS UNIX-V.2
DOS OS/DDP UNIX-V.3
EDX OS/2 UNIX-PC
ELF OS4 UNKNOWN
EMBOS OS86 UT2D
EMMOS OSX V
EPOS PCDOS VM
FOONEX PERQ/OS VM/370
FUZZ PLI VM/CMS
GCOS PSDOS/MIT VM/SP
GPOS PRIMOS VMS
HDOS RMX/RDOS VMS/EUNICE
IMAGEN ROS VRTX
INTERCOM RSX11M WAITS
IMPRESS RTE-A WANG
INTERLISP SATOPS WIN32
IOS SCO-XENIX/386 X11R3
IRIX SCS XDE
ISI-68020 SIMP XENIX
ITS SUN
6.3 Appendix C
Appendix C Installing DNS on a Sun when running NIS
====================
2) How to get DNS to be used when running NIS ?
First setup the appropriate /etc/resolv.conf file.
Something like this should do the "trick".
;
; Data file for a client.
;
domain local domain
nameserver address of primary domain nameserver
nameserver address of secondary domain nameserver
where: "local domain" is the domain part of the hostnames.
For example, if your hostname is "thor.ece.uc.edu"
your "local domain" is "ece.uc.edu".
You will need to put a copy of this resolv.conf on
all NIS(YP) servers including slaves.
Under SunOS 4.1 and greater, change the "B=" at the top
of the /var/yp/Makefile to "B=-b" and setup NIS in the
usual fashion.
You will need reboot or restart ypserv for these changes
to take affect.
Under 4.0.x, edit the Makefile or apply the following "diff":
*** Makefile.orig Wed Jan 10 13:22:11 1990
--- Makefile Wed Jan 10 13:22:01 1990
***************
*** 63 ****
! | $(MAKEDBM) - $(YPDBDIR)/$(DOM)/hosts.byname; \
--- 63 ----
! | $(MAKEDBM) -b - $(YPDBDIR)/$(DOM)/hosts.byname; \
***************
*** 66 ****
! | $(MAKEDBM) - $(YPDBDIR)/$(DOM)/hosts.byaddr; \
--- 66 ----
! | $(MAKEDBM) -b - $(YPDBDIR)/$(DOM)/hosts.byaddr; \
====================
--
Craig Richmond. Computer Officer - Dept of Economics (morning) 380 3860
University of Western Australia Dept of Education (afternoon) 2368
craig@ecel.uwa.edu.au Dvorak Keyboards RULE! "Messes are only acceptable
if users make them. Applications aren't allowed this freedom" I.M.VI 2-4
Being authoritive means that if a server is asked about something in that domain, it can say with no ambiguity whether or not a given piece of information is true. For example. We have domains x.z and y.z. There are by definition authoritive name servers for both of these domains and we shall assume that the name server in both of these cases is a machine called nic.x.z and nic.y.z but that really makes no difference.
If someone asks nic.x.z whether there is a machine called a.x.z, then nic.x.z can authoritively say, yes or no because it is the authoritive name server for that domain. If someone asks nic.x.z whether there is a machine called a.y.z then nic.x.z asks nic.y.z whether such a machine exists (and caches this for future requests). It asks nic.y.z because nic.y.z is the authoritive name server for the domain y.z. The information about authoritive name servers is stored in the DNS itself and as long as you have a pointer to a name server who is more knowledgable than yourself then you are set.
When a change is made, it propogates slowly out through the internet to eventually reach all machines. The following was supplied by Mark Andrews Mark.Andrews@syd.dms.csiro.au.
If both the primary and all secondaries are up and talking when a zone update occurs and for the refresh period after the update the old data will live for max(refresh + mininum) average (refresh/2 +mininum) for the zone. New information will be available from all servers after refresh.
So with a refresh of 3 hours and a minimum of a day, you can expect everything to be working a day after it is changed. If you have a longer minimum, it may take a couple of days before things return to normal.
There is also a difference between a zone and a domain. The domain is the entire set of machines that are contained within an organisational domain name. For example, the domain uwa.edu.au contains all the machines at the University of Western Australia. A Zone is the area of the DNS for which a server is responsible. The University of Western Australia is a large organisation and trying to track all changes to machines at a central location would be difficult. The authoritive name server for the zone uwa.edu.au delegates the authority for the zone ecel.uwa.edu.au to decel.ecel.uwa.edu.au. Machine foo.ecel.uwa.edu.au is in the zone that decel is authoritive for. Machine bar.uwa.edu.au is in the zone that uniwa.uwa.edu.au is authoritive for.
2 Installing the DNS:
First I'll assume you already have a copy of the Domain Name Server software. It is probably called named or in.named depending on your flavour of unix. I never had to get a copy, but if anyone thinks that information should be here then by all means tell me and I'll put it in. If you intend on using the package called BIND, then you should be sure that you get version 4.9.x, which is the most recent version at this point in time.
For more information on the latest version of BIND you should take a look at Internet Software Consortium which sponsors the development of BIND. - Kavli
2.1 The Boot File:
First step is to create the file named.boot. This describes to named (we'll dispense with the in.named. Take them to be the same) where the information that it requires can be found. This file is normally found in /etc/named.boot and I personally tend to leave it there because then I know where to find it. If you don't want to leave it there but place it in a directory with the rest of your named files, then there is usually an option on named to specify the location of the boot file.
An alternative is of course to make a symbolic link from /etc/named.boot to the wanted directory. - Kavli
Your typical boot file will look like this if you are an unimportant leaf node and there are other name servers at your site.
directory /etc/namedfiles
cache . root.cache
primary ecel.uwa.edu.au ecel.uwa.domain
primary 0.0.127.in-addr.arpa 0.0.127.domain
primary 4.95.130.in-addr.arpa 4.95.130.domain
forwarders 130.95.128.1
Here is an alternative layout used by Christophe Wolfhugel <Christophe.Wolfhugel@grasp.insa-lyon.fr> He finds this easier because of the large number of domains he has. The structure is essentially the same, but the file names use the domain name rather than the IP subnet to describe the contents.
directory /usr/local/etc/bind
cache . p/root
forwarders 134.214.100.1 192.93.2.4
;
; Primary servers
;
primary fr.net p/fr.net
primary frmug.fr.net p/frmug.fr.net
primary 127.in-addr.arpa p/127
;
; Secondary servers
;
secondary ensta.fr 147.250.1.1 s/ensta.fr
secondary gatelink.fr.net 134.214.100.1 s/gatelink.fr.net
secondary insa-lyon.fr 134.214.100.1 s/insa-lyon.fr
secondary loesje.org 145.18.226.21 s/loesje.org
secondary nl.loesje.org 145.18.226.21 s/nl.loesje.org
secondary pcl.ac.uk 161.74.160.5 s/pcl.ac.uk
secondary univ-lyon1.fr 134.214.100.1 s/univ-lyon1.fr
secondary wmin.ac.uk 161.74.160.5 s/wmin.ac.uk
secondary westminster.ac.uk 161.74.160.5 s/westminster.ac.uk
;
;
; Secondary for addresses
;
secondary 74.161.in-addr.arpa 161.74.160.5 s/161.74
secondary 214.134.in-addr.arpa 134.214.100.1 s/134.214
secondary 250.147.in-addr.arpa 147.250.1.1 s/147.250
;
; Classes C
;
secondary 56.44.192.in-addr.arpa 147.250.1.1 s/192.44.56
secondary 57.44.192.in-addr.arpa 147.250.1.1 s/192.44.57
The lines in the named.boot file have the following meanings.
directory
This is the path that named will place in front of all file names referenced from here on. If no directory is specified, it looks for files relative to /etc.
cache
This is the information that named uses to get started. Named must know the IP number of some other name servers at least to get started. Information in the cache is treated differently depending on your version of named. Some versions of named use the information included in the cache permenantly and others retain but ignore the cache information once up and running.
Be sure you get an up-to-date cache-file. An obsolete cache file is a good source of problems. - Kavli
primary
This is one of the domains for which this machine is authorative for. You put the entire domain name in. You need forwards and reverse lookups. The first value is the domain to append to every name included in that file. (There are some exceptions, but they will be explained later) The name at the end of the line is the name of the file (relative to /etc of the directory if you specified one). The filename can have slashes in it to refer to subdirectories so if you have a lot of domains you may want to split it up.
BE VERY CAREFUL TO PUT THE NUMBERS BACK TO FRONT FOR THE REVERSE LOOK UP FILE. The example given above is for the subnet ecel.uwa.edu.au whose IP address is 130.95.4.*. The reverse name must be 4.95.130.in-addr.arpa. It must be backwards and it must end with .in-addr.arpa. If your reverse name lookups don't work, check this. If they still don't work, check this again.
forwarders
This is a list of IP numbers for forward requests for sites about which we are unsure. A good choice here is the name server which is authoritive for the zone above you.
secondary (This line is not in the example, but is worth mentioning.)
A secondary line indicates that you wish to be a secondary name server for this domain. You do not need to do this usually. All it does is help make the DNS more robust. You should have at least one secondary server for your site, but you do not need to be a secondary server for anyone else. You can by all means, but you don't need to be. If you want to be a secondary server for another domain, then place the line
secondary gu.uwa.edu.au 130.95.100.3 130.95.128.1 sec/gu.uwa.edu.au
in your named.boot. This will make your named try the servers on both of the machines specified to see if it can obtain the information about those domains. You can specify a number of IP addresses for the machines to query that probably depends on your machine. Your copy of named will upon startup go and query all the information it can get about the domain in question and remember it and act as though it were authoritive for that domain.
Next you will want to start creating the data files that contain the name definitions.
2.2 The cache file:
You should always use the latest cache file. The simplest way to do this is by using dig(1) this way:
dig @ns.internic.net . ns > root.cache
You can also get a copy of the cache file by ftp'ing FTP.RS.INTERNIC.NET.
An example of a cache file is located in Appendix A.
2.3 The Forward Mapping file:
The file ecel.uwa.edu.au. will be used for the example with a couple of machines left in for the purpose of the exercise. Here is a copy of what the file looks like with explanations following.
; Authoritative data for ecel.uwa.edu.au
;
@ IN SOA decel.ecel.uwa.edu.au. postmaster.ecel.uwa.edu.au. (
93071200 ; Serial (yymmddxx)
10800 ; Refresh 3 hours
3600 ; Retry 1 hour
3600000 ; Expire 1000 hours
86400 ) ; Minimum 24 hours
IN A 130.95.4.2
IN MX 100 decel
IN MX 150 uniwa.uwa.edu.au.
IN MX 200 relay1.uu.net.
IN MX 200 relay2.uu.net.
localhost IN A 127.0.0.1
decel IN A 130.95.4.2
IN HINFO SUN4/110 UNIX
IN MX 100 decel
IN MX 150 uniwa.uwa.edu.au.
IN MX 200 relay1.uu.net
IN MX 200 relay2.uu.net
gopher IN CNAME decel.ecel.uwa.edu.au.
accfin IN A 130.95.4.3
IN HINFO SUN4/110 UNIX
IN MX 100 decel
IN MX 150 uniwa.uwa.edu.au.
IN MX 200 relay1.uu.net
IN MX 200 relay2.uu.net
chris-mac IN A 130.95.4.5
IN HINFO MAC-II MACOS
The comment character is ';' so the first two lines are just comments indicating the contents of the file.
All values from here on have IN in them. This indicates that the value is an InterNet record. There are a couple of other types, but all you need concern yourself with is internet ones.
The IN type is default and can safely be omitted. It looks better without them I think.
- Kavli
The SOA record is the Start Of Authority record. It contains the information that other nameservers will learn about this domain and how to treat the information they are given about it. The '@' as the first character in the line indicates that you wish to define things about the domain for which this file is responsible. The domain name is found in the named.boot file in the corresponding line to this filename. All information listed refers to the most recent machine/domain name so all records from the '@' until 'localhost' refer to the '@'. The SOA record has 5 magic numbers. First magic number is the serial number. If you change the file, change the serial number. If you don't, no other name servers will update their information. The old information will sit around for a very long time.
Refresh is the time between refreshing information about the SOA. Retry is the frequency of retrying if an authorative server cannot be contacted. Expire is how long a secondary name server will keep information about a zone without successfully updating it or confirming that the data is up to date. This is to help the information withstand fairly lengthy downtimes of machines or connections in the network without having to recollect all the information. Minimum is the default time to live value handed out by a nameserver for all records in a zone without an explicit TTL value. This is how long the data will live after being handed out. The two pieces of information before the 5 magic numbers are the machine that is considered the origin of all of this information. Generally the machine that is running your named is a good one for here. The second is an email address for someone who can fix any problems that may occur with the DNS. Good ones here are postmaster, hostmaster or root. NOTE: You use dots and not '@' for the email address.
eg: root.decel.ecel.uwa.edu.au is correct
and
root@decel.ecel.uwa.edu.au is incorrect.
If your name contains a dot: E.g. Ronny.Kavli@mailhost.somedomain.there. - you must escape the dot -> Ronny\.Kavli.mailhost.somedomain.there. - But, if possible, you should create a mailalias instead. That way, related mail can go to more than one person. - Kavli
We now have an address to map ecel.uwa.edu.au to. The address is 130.95.4.2 which happens to be decel, our main machine. If you try to find an IP number for the domain ecel.uwa.edu.au it will get you the machine decel.ecel.uwa.edu.au's IP number. This is a nicety which means that people who have non-MX record mailers can still mail fred@ecel.uwa.edu.au and don't have to find the name of a machine name under the domain to mail.
Now we have a couple of MX records for the domain itself. The MX records specify where to send mail destined for the machine/domain that the MX record is for. In this case we would prefer if all mail for fred@ecel.uwa.edu.au is sent to decel.ecel.uwa.edu.au. If that does not work, we would like it to go to uniwa.uwa.edu.au because there are a number of machines that might have no idea how to get to us, but may be able to get to uniwa. And failing that, try the site relay1.uu.net. A small number indicates that this site should be tried first. The larger the number the further down the list of sites to try the site is. NOTE: Not all machines have mailers that pay attention to MX records. Some only pay attention to IP numbers, which is really stupid. All machines are required to have MX-capable Mail Transfer Agents (MTA) as there are many addresses that can only be reached via this means.
Do not point an MX record to a CNAME record. A lot of mailers don't handle this. Add another A-record to it instead, but let the reverse table point to the real name. In other words: Don't add a PTR record to it. - Kavli
There is an entry for localhost now. Note that this is somewhat of a kludge and should probably be handled far more elegantly. By placing localhost here, a machine comes into existance called localhost.ecel.uwa.edu.au. If you finger it, or telnet to it, you get your own machine, because the name lookup returns 127.0.0.1 which is the special case for your own machine. I have used a couple of different DNS packages. The old BSD one let you put things into the cache which would always work, but would not be exported to other nameservers. In the newer Sun one, they are left in the cache and are mostly ignored once named is up and running. This isn't a bad solution, its just not a good one.
Decel is the main machine in our domain. It has the IP number 130.95.4.2 and that is what this next line shows. It also has a HINFO entry. HINFO is Host Info which is meant to be some sort of an indication of what the machine is and what it runs. The values are two white space seperated values. First being the hardware and second being the software. HINFO is not compulsory, its just nice to have sometimes. We also have some MX records so that mail destined for decel has some other avenues before it bounces back to the sender if undeliverable.
It is a good idea to give all machines capable of handling mail an MX record because this can be cached on remote machines and will help to reduce the load on the network.
gopher.ecel.uwa.edu.au is the gopher server in our division. Now because we are cheapskates and don't want to go and splurge on a seperate machine just for handling gopher requests we have made it a CNAME to our main machine. While it may seem pointless it does have one main advantage. When we discover that our placing terrabytes of popular quicktime movies on our gopher server (no we haven't and we don't intend to) causes an unbearable load on our main machine, we can quickly move the CNAME to point at a new machine by changing the name mentioned in the CNAME. Then the slime of the world can continue to get their essential movies with a minimal interuption to the network. Other good CNAMEs to maintain are things like ftp, mailhost, netfind, archie, whois, and even dns (though the most obvious use for this fails). It also makes it easier for people to find these services in your domain.
Regarding CNAME from dns: NS records must point to A records. Same for MX records. - Kavli
We should probably start using WKS records for things like gopher and whois rather than making DNS names for them. The tools are not in wide circulation for this to work though. (Plus all those comments in many DNS implementation of "Not implemented" next to the WKS record)
WKS == Well Known Services. - The different services a host is providing
- Kavli
Finally we have a macintosh which belongs to my boss. All it needs is an IP number, and we have included the HINFO so that you can see that it is in fact a macII running a Mac System. To get the list of preferred values, you should get a copy of RFC 1340. It lists lots of useful information such as /etc/services values, ethernet manufacturer hardware addresses, HINFO defualts and many others. I will include the list as it stands at the moment, but if any RFC superceeds 1340, then it will have a more complete list. See Appendix B for that list.
NOTE: If Chris had a very high profile and wanted his mac to appear like a fully connected unix machine as far as internet services were concerned, he could simply place an MX record such as
IN MX 100 decel
after his machine and any mail sent to chris@chris-mac.ecel.uwa.edu.au would be automatically rerouted to decel.
2.4 The Reverse Mapping File
The reverse name lookup is handled in a most bizarre fashion. Well it all makes sense, but it is not immediately obvious.
All of the reverse name lookups are done by finding the PTR record associated with the name w.x.y.z.in-addr.arpa. So to find the name associated with the IP number 1.2.3.4, we look for information stored in the DNS under the name 4.3.2.1.in-addr.arpa. They are organised this way so that when you are allocated a B class subnet for example, you get all of the IP numbers in the domain 130.95. Now to turn that into a reverse name lookup domain, you have to invert the numbers or your registered domains will be spread all over the place. It is a mess and you need not understand the finer points of it all. All you need to know is that you put the reverse name lookup files back to front.
Here is the sample reverse name lookup files to go with our example.
0.0.127.in-addr.arpa
--
; Reverse mapping of domain names 0.0.127.in-addr.arpa
; Nobody pays attention to this, it is only so 127.0.0.1 -> localhost.
@ IN SOA decel.ecel.uwa.edu.au. postmaster.ecel.uwa.edu.au. (
91061801 ; Serial (yymmddxx)
10800 ; Refresh 3 hours
3600 ; Retry 1 hour
3600000 ; Expire 1000 hours
86400 ) ; Minimum 24 hours
;
1 IN PTR localhost.ecel.uwa.edu.au.
--
4.95.130.in-addr.arpa
--
; reverse mapping of domain names 4.95.130.in-addr.arpa
;
@ IN SOA decel.ecel.uwa.edu.au. postmaster.ecel.uwa.edu.au. (
92050300 ; Serial (yymmddxx format)
10800 ; Refresh 3hHours
3600 ; Retry 1 hour
3600000 ; Expire 1000 hours
86400 ) ; Minimum 24 hours
2 IN PTR decel.ecel.uwa.edu.au.
3 IN PTR accfin.ecel.uwa.edu.au.
5 IN PTR chris-mac.ecel.uwa.edu.au.
--
It is important to remember that you must have a second start of authority record for the reverse name lookups. Each reverse name lookup file must have its own SOA record. The reverse name lookup on the 127 domain is debatable seeing as there is likely to be only one number in the file and it is blatantly obvious what it is going to map to.
In general: Each primary file pointed to in named.boot should have one - and only one - SOA record.
- Kavli
The SOA details are the same as in the forward mapping.
Each of the numbers listed down the left hand side indicates that the line contains information for that number of the subnet. Each of the subnets must be the more significant digits. eg the 130.95.4 of an IP number 130.95.4.2 is implicit for all numbers mentioned in the file.
The PTR must point to a machine that can be found in the DNS. If the name is not in the DNS, some versions of named just bomb out at this point.
Reverse name lookups are not compulsory, but nice to have. It means that when people log into machines, they get names indicating where they are logged in from. It makes it easier for you to spot things that are wrong and it is far less cryptic than having lots of numbers everywhere. Also if you do not have a name for your machine, some brain dead protocols such as talk will not allow you to connect.
Since I had this I had one suggestion of an alternative way to do the localhost entry. I think it is a matter of personal opinion so I'll include it here in case anyone things that this is a more appropriate method.
The following is courtesy of jep@convex.nl (JEP de Bie)
The way I did it was:
1) add in /etc/named.boot:
primary . localhost primary 127.in-addr.ARPA. IP127
(Craig: It has been suggested by Mark Andrews that this is a bad practice particularly if you have upgraded to Bind 4.9. You also run the risk of polluting the root name servers. This comes down to a battle of idealogy and practicality. Think twice before declaring yourself authorative for the root domain.)
So I not only declare myself (falsely? - probably, but nobody is going to listen anyway most likely [CPR]:-) athorative in the 127.in-addr.ARPA domain but also in the . (root) domain.
2) the file localhost has:
$ORIGIN .
localhost IN A 127.0.0.1
3) and the file IP127:
$ORIGIN 127.in-addr.ARPA.
1.0.0 IN PTR localhost.
4) and I have in my own domain file (convex.nl) the line:
$ORIGIN convex.nl.
localhost IN CNAME localhost.
The advantage (elegancy?) is that a query (A) of localhost. gives the reverse of the query of 1.0.0.127.in-addr.ARPA. And it also shows that localhost.convex.nl is only a nickname to something more absolute. (While the notion of localhost is of course relative :-)).
And I also think there is a subtle difference between the lines
primary 127.in-addr.ARPA. IP127
and
primary 0.0.127.in-addr.ARPA. 4.95.130.domain
=============
JEP de Bie
jep@convex.nl
=============
3 Delegating authority for domains within your domain
When you start having a very big domain that can be broken into logical and seperate 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 organisation so that they can manage themselves.
Another essential piece of information is that every domain that exists must have its 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 recognised 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.
4 Troubleshooting your named:
4.1 Named doesn't work! What is wrong?
Step 1: Run nslookup and see what nameserver it tries to connect you to. If nslookup connects you to the wrong nameserver, create a /etc/resolv.conf file that points your machine at the correct nameserver. If there is no resolv.conf file, the the resolver uses the nameserver on the local machine.
Step 2: Make sure that named is actually running.
Step 3: Restart named and see if you get any error messages on the console and in also check /usr/adm/messages.
Step 4: If named is running, nslookup connects to the appropriate nameserver and nslookup can answer simple questions, but other programs such as 'ping' do not work with names, then you need to install resolv+ most likely.
4.2 Local has noticed change, but nobody else has new info
I changed my named database and my local machine has noticed, but nobody else has the new information?
Change the serial number in the SOA for any domains that you modified and restart named. Wait an hour and check again. The information propogates out. It won't change immediately.
4.3 I can see their info, but they can't see mine
My local machine knows about all the name server information, but no other sites know about me?
Find an upstream nameserver (one that has an SOA for something in your domain) and ask them to be a secondary name server for you. eg if you are ecel.uwa.edu.au, ask someone who has an SOA for the domain uwa.edu.au. Get NS records (and glue) added to your parent zone for your zone. This is called delegating. It should be done formally like this or you will get inconsistant answers out of the DNS. ALL NAMSERVERS FOR YOUR ZONE SHOULD BE LISTED IN THIS MANNER.
4.4 Forward domain works, but not backwards
My forward domain names work, but the backward names do not?
Make sure the numbers are back to front and have the in-addr.arpa on the end.
Make sure your reverse zone is registered. For Class C nets this can be done by mailing to hostmaster@internic.net. For class A & B nets make sure that you are registeres with the primary for your net and that the net itself is registered with hostmaster@internic.net.
5 How to get useful information from nslookup:
Nslookup is a very useful program but I'm sure there are less than 20 people worldwide who know how to use it to its full usefulness. I'm most certainly not one of them. If you don't like using nslookup, there is at least one other program called dig, that has most/all(?) of the functionality of nslookup and is a hell of a lot easier to use.
I won't go into dig much here except to say that it is a lot easier to get this information out of. I won't bother because nslookup ships with almost all machines that come with network software.
To run nslookup, you usually just type nslookup. It will tell you the server it connects to. You can specify a different server if you want. This is useful when you want to tell if your named information is consistent with other servers.
5.1 Getting name to number mappings
Type the name of the machine. Typing 'decel' is enough if the machine is local.
(Once you have run nslookup successfully)
> decel
Server: ecel.uwa.edu.au
Address: 130.95.4.2
Name: decel.ecel.uwa.edu.au
Address: 130.95.4.2
>
One curious quirk of some name resolvers is that if you type a machine name, they will try a number of permutations. For example if my machine is in the domain ecel.uwa.edu.au and I try to find a machine called fred, the resolver will try the following.
fred.ecel.uwa.edu.au.
fred.uwa.edu.au.
fred.edu.au.
fred.au.
fred.
This can be useful, but more often than not, you would simply prefer a good way to make aliases for machines that are commonly referenced. If you are running resolv+, you should just be able to put common machines into the host file.
DIG: dig <machine name>
5.2 Getting number to name mappings
Nslookup defaults to finding you the Address of the name specified. For reverse lookups you already have the address and you want to find the name that goes with it. If you read and understood the bit above where it describes how to create the number to name mapping file, you would guess that you need to find the PTR record instead of the A record. So you do the following.
> set type=ptr
> 2.4.95.130.in-addr.arpa
Server: decel.ecel.uwa.edu.au
Address: 130.95.4.2
2.4.95.130.in-addr.arpa host name = decel.ecel.uwa.edu.au
>
nslookup tells you that the ptr for the machine name 2.4.95.130.in-addr.arpa points to the host decel.ecel.uwa.edu.au.
DIG: dig -x <machine number>
5.3 Finding where mail goes when a machine has no IP number
When a machine is not IP connected, it needs to specify to the world, where to send the mail so that it can dial up and collect it every now and then. This is accomplished by setting up an MX record for the site and not giving it an IP number. To get the information out of nslookup as to where the mail goes, do the following.
> set type=mx
> dialix.oz.au
Server: decel.ecel.uwa.oz.au
Address: 130.95.4.2
Non-authoritative answer:
dialix.oz.au preference = 100, mail exchanger = uniwa.uwa.OZ.AU
dialix.oz.au preference = 200, mail exchanger = munnari.OZ.AU
Authoritative answers can be found from:
uniwa.uwa.OZ.AU inet address = 130.95.128.1
munnari.OZ.AU inet address = 128.250.1.21
munnari.OZ.AU inet address = 192.43.207.1
mulga.cs.mu.OZ.AU inet address = 128.250.35.21
mulga.cs.mu.OZ.AU inet address = 192.43.207.2
dmssyd.syd.dms.CSIRO.AU inet address = 130.155.16.1
ns.UU.NET inet address = 137.39.1.3
You tell nslookup that you want to search for mx records and then you give it the name of the machine. It tells you the preference for the mail (small means more preferable), and who the mail should be sent to. It also includes sites that are authorative (have this name in their named database files) for this MX record. There are multiple sites as a backup. As can be seen, our local public internet access company dialix would like all of their mail to be sent to uniwa, where they collect it from. If uniwa is not up, send it to munnari and munnari will get it to uniwa eventually.
NOTE: For historical reasons Australia used to be .oz which was changed to .oz.au to move to the ISO standard extensions upon the advent of IP. We are now moving to a more normal heirarchy which is where the .edu.au comes from. Pity, I liked having oz.
DIG: dig <zone> mx
5.4 Getting a list of machines in a domain from nslookup
Find a server that is authorative for the domain or just generally all knowing. To find a good server, find all the SOA records for a given domain. To do this, you set type=soa and enter the domain just like in the two previous examples.
Once you have a server type
> ls gu.uwa.edu.au.
[uniwa.uwa.edu.au]
Host or domain name Internet address
gu server = mackerel.gu.uwa.edu.au
gu server = uniwa.uwa.edu.au
gu 130.95.100.3
snuffle-upagus 130.95.100.131
mullet 130.95.100.2
mackerel 130.95.100.3
marlin 130.95.100.4
gugate 130.95.100.1
gugate 130.95.100.129
helpdesk 130.95.100.180
lan 130.95.100.0
big-bird 130.95.100.130
To get a list of all the machines in the domain.
If you wanted to find a list of all of the MX records for the domain, you can put a -m flag in the ls command.
> ls -m gu.uwa.edu.au.
[uniwa.uwa.edu.au]
Host or domain name Metric Host
gu 100 mackerel.gu.uwa.edu.au
gu 200 uniwa.uwa.edu.au
This only works for a limited selection of the different types.
DIG: dig axfr <zone> @<server>
6 Appendicies
6.2 Appendix B
An Excerpt from
RFC 1340 Assigned Numbers July 1992
MACHINE NAMES
These are the Official Machine Names as they appear in the Domain Name
System HINFO records and the NIC Host Table. Their use is described in
RFC-952 [53].
A machine name or CPU type may be up to 40 characters taken from the
set of uppercase letters, digits, and the two punctuation characters
hyphen and slash. It must start with a letter, and end with a letter
or digit.
ALTO DEC-1080
ALTOS-6800 DEC-1090
AMDAHL-V7 DEC-1090B
APOLLO DEC-1090T
ATARI-104ST DEC-2020T
ATT-3B1 DEC-2040
ATT-3B2 DEC-2040T
ATT-3B20 DEC-2050T
ATT-7300 DEC-2060
BBN-C/60 DEC-2060T
BURROUGHS-B/29 DEC-2065
BURROUGHS-B/4800 DEC-FALCON
BUTTERFLY DEC-KS10
C/30 DEC-VAX-11730
C/70 DORADO
CADLINC DPS8/70M
CADR ELXSI-6400
CDC-170 EVEREX-386
CDC-170/750 FOONLY-F2
CDC-173 FOONLY-F3
CELERITY-1200 FOONLY-F4
CLUB-386 GOULD
COMPAQ-386/20 GOULD-6050
COMTEN-3690 GOULD-6080
CP8040 GOULD-9050
CRAY-1 GOULD-9080
CRAY-X/MP H-316
CRAY-2 H-60/68
CTIWS-117 H-68
DANDELION H-68/80
DEC-10 H-89
DEC-1050 HONEYWELL-DPS-6
DEC-1077 HONEYWELL-DPS-8/70
HP3000 ONYX-Z8000
HP3000/64 PDP-11
IBM-158 PDP-11/3
IBM-360/67 PDP-11/23
IBM-370/3033 PDP-11/24
IBM-3081 PDP-11/34
IBM-3084QX PDP-11/40
IBM-3101 PDP-11/44
IBM-4331 PDP-11/45
IBM-4341 PDP-11/50
IBM-4361 PDP-11/70
IBM-4381 PDP-11/73
IBM-4956 PE-7/32
IBM-6152 PE-3205
IBM-PC PERQ
IBM-PC/AT PLEXUS-P/60
IBM-PC/RT PLI
IBM-PC/XT PLURIBUS
IBM-SERIES/1 PRIME-2350
IMAGEN PRIME-2450
IMAGEN-8/300 PRIME-2755
IMSAI PRIME-9655
INTEGRATED-SOLUTIONS PRIME-9755
INTEGRATED-SOLUTIONS-68K PRIME-9955II
INTEGRATED-SOLUTIONS-CREATOR PRIME-2250
INTEGRATED-SOLUTIONS-CREATOR-8 PRIME-2655
INTEL-386 PRIME-9955
INTEL-IPSC PRIME-9950
IS-1 PRIME-9650
IS-68010 PRIME-9750
LMI PRIME-2250
LSI-11 PRIME-750
LSI-11/2 PRIME-850
LSI-11/23 PRIME-550II
LSI-11/73 PYRAMID-90
M68000 PYRAMID-90MX
MAC-II PYRAMID-90X
MASSCOMP RIDGE
MC500 RIDGE-32
MC68000 RIDGE-32C
MICROPORT ROLM-1666
MICROVAX S1-MKIIA
MICROVAX-I SMI
MV/8000 SEQUENT-BALANCE-8000
NAS3-5 SIEMENS
NCR-COMTEN-3690 SILICON-GRAPHICS
NEXT/N1000-316 SILICON-GRAPHICS-IRIS
NOW SGI-IRIS-2400
SGI-IRIS-2500 SUN-3/50
SGI-IRIS-3010 SUN-3/60
SGI-IRIS-3020 SUN-3/75
SGI-IRIS-3030 SUN-3/80
SGI-IRIS-3110 SUN-3/110
SGI-IRIS-3115 SUN-3/140
SGI-IRIS-3120 SUN-3/150
SGI-IRIS-3130 SUN-3/160
SGI-IRIS-4D/20 SUN-3/180
SGI-IRIS-4D/20G SUN-3/200
SGI-IRIS-4D/25 SUN-3/260
SGI-IRIS-4D/25G SUN-3/280
SGI-IRIS-4D/25S SUN-3/470
SGI-IRIS-4D/50 SUN-3/480
SGI-IRIS-4D/50G SUN-4/60
SGI-IRIS-4D/50GT SUN-4/110
SGI-IRIS-4D/60 SUN-4/150
SGI-IRIS-4D/60G SUN-4/200
SGI-IRIS-4D/60T SUN-4/260
SGI-IRIS-4D/60GT SUN-4/280
SGI-IRIS-4D/70 SUN-4/330
SGI-IRIS-4D/70G SUN-4/370
SGI-IRIS-4D/70GT SUN-4/390
SGI-IRIS-4D/80GT SUN-50
SGI-IRIS-4D/80S SUN-100
SGI-IRIS-4D/120GTX SUN-120
SGI-IRIS-4D/120S SUN-130
SGI-IRIS-4D/210GTX SUN-150
SGI-IRIS-4D/210S SUN-170
SGI-IRIS-4D/220GTX SUN-386i/250
SGI-IRIS-4D/220S SUN-68000
SGI-IRIS-4D/240GTX SYMBOLICS-3600
SGI-IRIS-4D/240S SYMBOLICS-3670
SGI-IRIS-4D/280GTX SYMMETRIC-375
SGI-IRIS-4D/280S SYMULT
SGI-IRIS-CS/12 TANDEM-TXP
SGI-IRIS-4SERVER-8 TANDY-6000
SPERRY-DCP/10 TEK-6130
SUN TI-EXPLORER
SUN-2 TP-4000
SUN-2/50 TRS-80
SUN-2/100 UNIVAC-1100
SUN-2/120 UNIVAC-1100/60
SUN-2/130 UNIVAC-1100/62
SUN-2/140 UNIVAC-1100/63
SUN-2/150 UNIVAC-1100/64
SUN-2/160 UNIVAC-1100/70
SUN-2/170 UNIVAC-1160
UNKNOWN
VAX-11/725
VAX-11/730
VAX-11/750
VAX-11/780
VAX-11/785
VAX-11/790
VAX-11/8600
VAX-8600
WANG-PC002
WANG-VS100
WANG-VS400
WYSE-386
XEROX-1108
XEROX-8010
ZENITH-148
SYSTEM NAMES
These are the Official System Names as they appear in the Domain Name
System HINFO records and the NIC Host Table. Their use is described
in RFC-952 [53].
A system name may be up to 40 characters taken from the set of upper-
case letters, digits, and the three punctuation characters hyphen,
period, and slash. It must start with a letter, and end with a
letter or digit.
AEGIS LISP SUN OS 3.5
APOLLO LISPM SUN OS 4.0
AIX/370 LOCUS SWIFT
AIX-PS/2 MACOS TAC
BS-2000 MINOS TANDEM
CEDAR MOS TENEX
CGW MPE5 TOPS10
CHORUS MSDOS TOPS20
CHRYSALIS MULTICS TOS
CMOS MUSIC TP3010
CMS MUSIC/SP TRSDOS
COS MVS ULTRIX
CPIX MVS/SP UNIX
CTOS NEXUS UNIX-BSD
CTSS NMS UNIX-V1AT
DCN NONSTOP UNIX-V
DDNOS NOS-2 UNIX-V.1
DOMAIN NTOS UNIX-V.2
DOS OS/DDP UNIX-V.3
EDX OS/2 UNIX-PC
ELF OS4 UNKNOWN
EMBOS OS86 UT2D
EMMOS OSX V
EPOS PCDOS VM
FOONEX PERQ/OS VM/370
FUZZ PLI VM/CMS
GCOS PSDOS/MIT VM/SP
GPOS PRIMOS VMS
HDOS RMX/RDOS VMS/EUNICE
IMAGEN ROS VRTX
INTERCOM RSX11M WAITS
IMPRESS RTE-A WANG
INTERLISP SATOPS WIN32
IOS SCO-XENIX/386 X11R3
IRIX SCS XDE
ISI-68020 SIMP XENIX
ITS SUN
6.3 Appendix C
Appendix C Installing DNS on a Sun when running NIS
====================
2) How to get DNS to be used when running NIS ?
First setup the appropriate /etc/resolv.conf file.
Something like this should do the "trick".
;
; Data file for a client.
;
domain local domain
nameserver address of primary domain nameserver
nameserver address of secondary domain nameserver
where: "local domain" is the domain part of the hostnames.
For example, if your hostname is "thor.ece.uc.edu"
your "local domain" is "ece.uc.edu".
You will need to put a copy of this resolv.conf on
all NIS(YP) servers including slaves.
Under SunOS 4.1 and greater, change the "B=" at the top
of the /var/yp/Makefile to "B=-b" and setup NIS in the
usual fashion.
You will need reboot or restart ypserv for these changes
to take affect.
Under 4.0.x, edit the Makefile or apply the following "diff":
*** Makefile.orig Wed Jan 10 13:22:11 1990
--- Makefile Wed Jan 10 13:22:01 1990
***************
*** 63 ****
! | $(MAKEDBM) - $(YPDBDIR)/$(DOM)/hosts.byname; \
--- 63 ----
! | $(MAKEDBM) -b - $(YPDBDIR)/$(DOM)/hosts.byname; \
***************
*** 66 ****
! | $(MAKEDBM) - $(YPDBDIR)/$(DOM)/hosts.byaddr; \
--- 66 ----
! | $(MAKEDBM) -b - $(YPDBDIR)/$(DOM)/hosts.byaddr; \
====================
--
Craig Richmond. Computer Officer - Dept of Economics (morning) 380 3860
University of Western Australia Dept of Education (afternoon) 2368
craig@ecel.uwa.edu.au Dvorak Keyboards RULE! "Messes are only acceptable
if users make them. Applications aren't allowed this freedom" I.M.VI 2-4
0 comments:
Post a Comment