Recursive DNS serving

# Using MaraDNS as a recursive DNS server

This document is a step-by-step guide to setting up MaraDNS as a recursive DNS server. It assumes that MaraDNS is already compiled and installed.

## Table of contents

- Basic configuration
- Using MaraDNS on a slow network
- Using other recursive DNS servers
- Using different root servers
- Having private host names
- Using authoritative records for private names
- Private names with custom root servers
- Customizing the resolution of some names

## Basic configuration

Once MaraDNS is installed, the `mararc` file needs to be set up before MaraDNS will function as a recursive DNS server. This file only needs to be three lines long:

    ipv4_bind_addresses = "127.0.0.1"
    chroot_dir = "/etc/maradns"
    recursive_acl = "127.0.0.1"

This three-line file needs to be called `/etc/mararc`.

The first line is the IP address or addresses MaraDNS will use. Here, it has the address 127.0.0.1, which means that only the machine running MaraDNS will be able to access the MaraDNS server--other machines will not be able to see it.

If the machine running MaraDNS will be accessed by other machines, this IP needs to be changed to an IP that the machine running MaraDNS has.

It is possible to have MaraDNS run on multiple IP addresses:

    ipv4_bind_addresses = "10.1.3.2, 192.168.0.1, 127.0.0.1"

The second line, `chroot_dir` is the directory MaraDNS will be run from. When MaraDNS is being used as a recursive DNS server, this just has to be an empty directory, ideally owned by the root user.

The third line, `recursive_acl`, determines the range of IPs that can access the recursive DNS server. This is in IP/netmask format. For example, if one has an office which uses IPs in the form 192.168.1.1, 192.168.1.2, etc., and wishes to have only 192.168.1.any be allowed to make recursive queries:

    recursive_acl = "192.168.1.0/24"

Here the "/24" indicates that we ignore the fourth number in an IP when determining who can contact MaraDNS.

Once this is done, other machines can contact the MaraDNS server to perform DNS queries. For example, MaraDNS is now a DNS server which Windows 98 can use in "Control Panel -> Network -> TCP/IP -> DNS configuration", or a UNIX system can point to from `/etc/resolv.conf`.

## Using MaraDNS on a slow network

MaraDNS, on a slow network, may time out. MaraDNS normally only waits two seconds for a reply from a remote DNS server. This is not enough time to process queries on some slow networks. This can be changed by increasing the `timeout_seconds` value.

Here is a mararc file which waits six seconds (instead of the default two) for a reply from a remote DNS server:

    ipv4_bind_addresses = "127.0.0.1"
    chroot_dir = "/etc/maradns"
    recursive_acl = "127.0.0.1"
    timeout_seconds = 6

## Using other recursive DNS servers

It is possible to have MaraDNS contact other recursive name servers, instead of contacting the actual root servers to process recursive queries by using the variable `upstream_servers` in the mararc file.

In other words, one can use one's, say, ISP's DNS servers to resolve the names, and have MaraDNS act as a cache for the ISP's DNS servers. Supposing that the ISP name servers have the IPs 10.66.77.88 and 10.99.11.22, the mararc file will look like this:

    ipv4_bind_addresses = "127.0.0.1"
    chroot_dir = "/etc/maradns"
    recursive_acl = "127.0.0.1"
    upstream_servers = {}
    upstream_servers["."] = "10.66.77.88, 10.99.11.22"

## Using different root servers

MaraDNS, by default, uses the ICANN name servers as the root name servers. The reason for this default is practical: In my experience, the ICANN root name servers are the ones which least frequently change their IP addresses. They are the best name servers for simple "set and forget" recursive environments.

It is possible, however, to change the root DNS servers used by setting the `root_servers` variable in the mararc file. Here is what such a recursive configuration (this example uses the ICANN root servers; change this example to use another set of root servers as needed) looks like:

    ipv4_bind_addresses = "127.0.0.1"
    chroot_dir = "/etc/maradns"
    recursive_acl = "127.0.0.1"
    ipv4_alias = {}
    ipv4_alias["icann"]  = "198.41.0.4,"
    ipv4_alias["icann"] += "192.228.79.201,"
    ipv4_alias["icann"] += "192.33.4.12,"
    ipv4_alias["icann"] += "128.8.10.90,"
    ipv4_alias["icann"] += "192.203.230.10,"
    ipv4_alias["icann"] += "192.5.5.241,"
    ipv4_alias["icann"] += "192.112.36.4,"
    ipv4_alias["icann"] += "128.63.2.53,"
    ipv4_alias["icann"] += "192.36.148.17,"
    ipv4_alias["icann"] += "192.58.128.30,"
    ipv4_alias["icann"] += "193.0.14.129,"
    ipv4_alias["icann"] += "199.7.83.42,"
    ipv4_alias["icann"] += "202.12.27.33"
    root_servers["."] = "icann"

This file will do the exact same thing as the following `mararc` file:

    ipv4_bind_addresses = "127.0.0.1"
    chroot_dir = "/etc/maradns"
    recursive_acl = "127.0.0.1"

The ICANN servers listed above are the ones that MaraDNS uses when no root servers are specified.

As an aside, the `ipv4_alias` variable is a general purpose way of giving names to any set of IPs in a `mararc` file. We can use shortcuts like this, in fact:

    ipv4_alias = {}
    ipv4_alias["localhost"] = "127.0.0.1"
    ipv4_bind_addresses = "localhost"
    chroot_dir = "/etc/maradns"
    recursive_acl = "localhost"
    ipv4_alias["icann-a"] = "198.41.0.4"
    ipv4_alias["icann-b"] = "192.228.79.201"
    ipv4_alias["icann-c"] = "192.33.4.12"
    ipv4_alias["icann-d"] = "128.8.10.90"
    ipv4_alias["icann-e"] = "192.203.230.10"
    ipv4_alias["icann-f"] = "192.5.5.241"
    ipv4_alias["icann-g"] = "192.112.36.4"
    ipv4_alias["icann-h"] = "128.63.2.53"
    ipv4_alias["icann-i"] = "192.36.148.17"
    ipv4_alias["icann-j"] = "192.58.128.30"
    ipv4_alias["icann-k"] = "193.0.14.129"
    ipv4_alias["icann-l"] = "199.7.83.42"
    ipv4_alias["icann-m"] = "202.12.27.33"
    ipv4_alias["icann"] = "icann-a,icann-b,icann-c,icann-d,icann-e,icann-f,"
    ipv4_alias["icann"] += "icann-g,icann-h,icann-i,icann-j,icann-k,icann-l,"
    ipv4_alias["icann"] += "icann-m"
    root_servers["."] = "icann"

This works the same as the above two examples. The reason why we don't have commas in any of the aliases besides icann is because the comma before the quote is only needed on a line before a line that uses the `+=` operator.

Here is what a configuration file which uses OpenNIC's glue root servers as the root servers. This list is current as of February 22, 2006; note that OpenNIC frequently changes these IPs and you need to verify that these IPs are current at http://www.opennic.unrated.net/. A number of alternate root server organizations no longer exist; please make sure these people still exist before using this list.

    ipv4_bind_addresses = "127.0.0.1"
    chroot_dir = "/etc/maradns"
    recursive_acl = "127.0.0.1"
    ipv4_alias = {}
    # This ends with a comma because the next line is a += line
    ipv4_alias["opennic"]  = "131.161.247.232,"
    ipv4_alias["opennic"] += "208.185.249.250,"
    ipv4_alias["opennic"] += "66.227.42.140,"
    ipv4_alias["opennic"] += "66.227.42.149,"
    ipv4_alias["opennic"] += "64.81.44.251,"
    ipv4_alais["opennic"] += "216.87.84.214,"
    ipv4_alias["opennic"] += "208.185.249.251,"
    ipv4_alias["opennic"] += "131.161.247.231,"
    # This is the last line, so no comma at the end
    ipv4_alias["opennic"] += "65.243.92.254"
    # Considering how often alternate root DNS server lists change or disappear,
    # we will have the ICANN list on hand as a backup.
    ipv4_alias["icann"]  = "198.41.0.4,"
    ipv4_alias["icann"] += "192.228.79.201,"
    ipv4_alias["icann"] += "192.33.4.12,"
    ipv4_alias["icann"] += "128.8.10.90,"
    ipv4_alias["icann"] += "192.203.230.10,"
    ipv4_alias["icann"] += "192.5.5.241,"
    ipv4_alias["icann"] += "192.112.36.4,"
    ipv4_alias["icann"] += "128.63.2.53,"
    ipv4_alias["icann"] += "192.36.148.17,"
    ipv4_alias["icann"] += "192.58.128.30,"
    ipv4_alias["icann"] += "193.0.14.129,"
    ipv4_alias["icann"] += "198.32.64.12,"
    ipv4_alias["icann"] += "202.12.27.33"
    # Now, set the root servers; chance this to icann if you want to use the
    # icann servers instead.
    root_servers["."] = "opennic"

## Having private host names

One may wish to have private host names when running MaraDNS as a recursive name server. These are names that are not attached to the root servers, but will resolve on the recursive name server. For example, it might make sense to have "router.office." resolve to the IP of a router in an office.

There are two ways to do this with MaraDNS: By using a custom root server for only names that end in "office", or by having the authoritative half of MaraDNS handle custom name resolutions.

## Using authoritative records for private names

We can have local names by taking advantage of the fact that MaraDNS can act as both a recursive and authoritative name server on the same IP. MaraDNS first looks up authoritative names before performing recursion. For example, if `www.google.com` is defined in a MaraDNS zone file, MaraDNS will use the value in the zone file instead of contacting nameservers on the internet to get the IP for `www.google.com`.

The procedure to do this is as follows:

- Have an authoritative and recursive DNS server share the same IP. Make sure this DNS server is not accessible from the public internet.
- For this authoritative server, have zone files for the zones which one wants to have non-public information. Recursive queries will be resolved as usual (since the authoritative server is also a recursive server); authoritative queries for the special zones will get the special data.
- The maradns man page has a section on firewall configuration which describes how to set up an IP filter to allow MaraDNS to send packets. Basically, don't allow outside IPs to hit this combined server on port 53 (UDP); instead allow UDP connections to ports 15000-19095.

Here is how the configuration may look:

    ipv4_bind_addresses = "192.168.0.1"
    chroot_dir = "/etc/maradns"
    recursive_acl = "192.168.0.0/24"
    csv2 = {}
    csv2["office."] = "db.office"

Replace 192.168.0.1 with the IP of the machine running the recursive MaraDNS; replace 192.168.0.0/24 (This means "anything that begins with 192.168.0") with the IP range allowed to access the recursive DNS server.

The file "db.example.com." will be a csv2 zone file with records for the bogus example.com domain, such as router.example.com.

If you want to have some of these private names be CNAMES for hostnames on the internet (e.g. "google.example.com. CNAME www.google.com."), please read the dangling CNAME document.

More information on having host names for an internal network is available in the network section of the authoritative document.

## Private names with custom root servers

MaraDNS, starting with version 1.3.02, can have custom root name servers that only resolve names in a subtree of the DNS space. In other words, we can tell MaraDNS to have 192.168.0.7 resolve all names ending in `office` by having a line like this in one's mararc file:

    root_servers["office."] = "192.168.0.7"

Here is how a configuration may look on 192.168.0.1, the recursive server:

    ipv4_bind_addresses = "192.168.0.1"
    chroot_dir = "/etc/maradns"
    recursive_acl = "192.168.0.0/24"
    root_servers = {}
    root_servers["office."] = "192.168.0.7"

And the configuration on 192.168.0.7, the authoritative server:

    ipv4_bind_addresses = "192.168.0.7"
    chroot_dir = "/etc/maradns"
    csv2 = {}
    csv2["office."] = "db.office"

## Customizing the resolution of some names

One may wish to customize the resolution of certain names when using MaraDNS as both an authoritative and recursive name server. For example, if a high-profile domain is hijacked (such as what happened with panix.com in January of 2005), it may be desirable to have the correct name for the domain be temporarily locally set. This is also useful for a list of blocked sites (so the user gets a friendly "this site is blocked" instead of just being unable to connect to the site in question), and for setups where some machines need special DNS resolution for names that other machines do not need DNS resolution for.

The procedure for doing this is almost identical to the procedure for having private host names as described above. Here is an example relevant `mararc` file:

    ipv4_bind_addresses = "192.168.0.1"
    chroot_dir = "/etc/maradns"
    recursive_acl = "192.168.0.0/24"
    csv2 = {}
    csv2["example.com."] = "db.example.com"

The only things that need to be changed in this mararc file are the `ipv4_bind_addresses` and the `recursive_acl` parameters. The `csv2["example.com."]` is not changed.

Now, let us suppose we want to have the A records for "www.phishsite.foo" and "phishsite.foo" resolve to an IP address that we control the web site for. We would add the following records (lines) to the file `/etc/maradns/db.example.com`

    www.phishsite.foo. 192.168.0.2
    phishsite.foo. 192.168.0.2

We can also add a star record:

    *.phishsite.foo. 192.168.0.2