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Reverse DNS: Difference between revisions
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→3. in-addr.arpa or ip6.arpa Zone
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Because of the way DNS works, control is delegated at each level, so <code>my.firebrick.co.uk</code> is delegated so that the name servers for <code>co.uk</code> tell the name servers for <code>firebrick.co.uk</code> and so on. This is normally only at a couple of levels but it could be that at each level control of the domains below that level (i.e. with anything added to the start of the domain) is delegated to a new name server.
With IP addresses the control is delegated the other way, e.g. <code>217.''x.x.x''</code> is delegated to RIPE, and <code>217.169.0.''x''</code> is delegated to AAISP. To allow DNS to be used to turn IP addresses
To delegate your IP addresses to you we have to find a way to delegate within the block of 256 addresses we have received from RIPE. Few customers have a complete block of 256 addresses. Those that do can simply be set up so that their own name servers are used in the delegation from RIPE. For anyone with less than 256 addresses we have to find a way to give you some of the addresses within a block - which DNS does not allow.
<code>1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa</code>
==2. A+Reverse or AAAA+Reverse DNS records on a Domain We Host ==
Where you have a domain that we manage in our DNS, and want an IP we manage to refer to and from that name. To do this you can create an A+reverse record or an AAAA+Reverse in your domain DNS entries (instead of simply an A or AAAA record). This will automatically complete the corresponding reverse entry in our DNS mapping the IP address back to the name.This is usually the simplest way to handle reverse DNS when you also have a domain with us.
[[File:Reverse-dns-a-reverse.png|border]]
===
If you administer a domain that is not hosted with us, then '''we''' can add an entry into our control system specifying your choice of domain name (optionally including subdomains) specifically to then allow you to set up entries on our systems that will define a number of individual reverse lookup mappings from your AAISP addresses to individual names below your ‘base’ domain name. There is no charge for this
An example is given in the next section. On our systems you will define a number of records, one (or more) per address of yours, and we append your chosen domain name to each to form a reverse lookup (PTR) record that we define and publish for you. You can ask for several of your domain names to be set up on our systems. Such a domain name can include your choice of subdomain in your request.
===How to:===
For example, suppose you have an IP address from us such as <code>198.51.100.10</code> and you wish to define a PTR mapping (reverse lookup) to the name <code>fred-workstation.your-domain.example.com</code>.Important: If this domain is not hosted by us, you must first have asked staff to set up <code>your-domain.example.com</code> in our control system, but you only need to do so once. Then you would go into our control panel system, go to ''"Domains"'' and select the entry <code>your-domain.example.com</code> which we will have added for you following your request. Now for each individual reverse lookup entry you wish to define, enter for example the name <code>"fred-workstation"</code> into the first edit box. The value is not restricted to be just one single DNS label; it could contain dots for subdomains. Then enter the IP address in the edit box below, in this case <code>198.51.100.10</code>. You must remember to then click '''OK''' or '''Apply''' to create the record. You will see that a new record is now listed below.
Notice there is an option to select "ipv4 reverse" or "ipv6 reverse" lookup - IPv4 is correct in this example case. The procedure for IPv6 address reverse lookups is the same, just click the pop-out menu and select "ipv6 reverse".
You can also amend existing records or delete them by first clicking on one entry in the list of records below so that it becomes highlighted. You can then either alter the details of the record and then click '''Apply''', or you can click an ‘Erase’ button on the right.
==3. in-addr.arpa or ip6.arpa Zone==
[[File:Reverse-dns-inaddrarpa.png|border]]
<code>1.hosts.testing.me.uk</code>
<code>2.hosts.testing.me.uk</code>
etc.…
Contact support staff for this.
This setting is found on the control pages under the link to your Login. This will apply to IPv4 and [[IPv6]].
===1. Delegation by NS===
Delegation by NS works by putting your name server in our DNS for each of your addresses. e.g. if you had <code>217.169.0.0-3</code> then we would put your name servers for each entry <code>0.0.169.217.in-addr.arpa</code>, <code>1.0.169.217.in-addr.arpa</code>, <code>2.0.169.217.in-addr.arpa</code>, <code>3.0.169.217.in-addr.arpa</code>. This would mean you can create four separate zone files each of which has normal SOA records etc., and a single PTR record with the name for that IP address. This is logically the correct way of doing it as the reverse DNS zone is delegated at each level of control right down to the IP address level. It is rather tedious to set up lots of zone files though, especially if you have, say, 128 addresses.
Remember that you also have a WAN address which may be completely different from your other addresses, and the reverse DNS is also delegated to your name servers for this too.
===2. Delegation by CNAME ===
Delegation by CNAME is a way to delegate a block of addresses to you so that you only have one zone file to worry about. The way this works is that we put a CNAME record for each address indicating that the answer is found under a different name. We then delegate that different name to your name servers. There are several ways to do this, but we use the system of <code>''first''-''last''.''restofzone''.in-addr.arpa</code>. e.g. if you had <code>217.169.0.0</code>-<code>3</code> we would delegate a zone <code>0-3.0.169.217.in-addr.arpa</code> to your name server(s) and add CNAME entries for each IP, e.g. <code>1.0.169.217.in-addr.arpa</code> with CNAME to <code>1.0-3.0.169.217.in-addr.arpa</code>.
Your WAN address and any other single addresses are still individually delegated as their own zone as above.
===IPv6 Reverse Delegation===
IPv6 is delegated at /48 or lower by NS
===Reverse Delegation for /24 or larger===
If you have a block of 256 addresses or more, then reverse DNS delegation is done at the /24 level and setting CNAME or NS has the same effect. This means you are responsible for an entire reverse zone without the need for special CNAME entries, etc. Most people do not have such a large block of addresses.
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