krypted.com

Tiny Deathstars of Foulness

DNS is an integral service to most modern networks. The Domain Name System, or DNS is comprised of hierarchical and decentralized Domain Name Servers, or DNS Servers. This is how we connect to computers and the websites that reside on computers by their names, rather than having to memorize the IP addresses of every single computer out there. So you get to type krypted.com and come to my website instead of typing the IP address. Or more likely, Facebook.com, but just because my website is older, I’m not mad about that. No really…

So you have a macOS Server and you need to take your DNS records out of it and move them to another solution. Luckily, DNS on any operating system is one of the easiest to manage. So let’s start by dumping all of our DNS records:

/Applications/Server.app/Contents/ServerRoot/System/Library/PrivateFrameworks/DNSManager.framework/dnsconfig list

ACLs:
    com.apple.ServerAdmin.DNS.public
Options:
    directory: /Library/Server/named
    allow-recursion: com.apple.ServerAdmin.DNS.public 
    allow-transfer: none 
    forwarders: 8.8.8.8 4.4.4.4 
Views:
    com.apple.ServerAdmin.DNS.public
        Zones:
            test.com
                Options:
                    allow-transfer: none 
                    allow-update: none 
                Resource Recs:
                        testalias.test.com (CNAME)
                        test.com (SOA)
                        test.com (NS)
                        test.com (MX)
                        test.test.com (A)
                Resource Recs:
                    no resource recs
            0.0.127.in-addr.arpa
                Options:
                    allow-update: none 
                Resource Recs:
                        0.0.127.in-addr.arpa (SOA)
                        0.0.127.in-addr.arpa (NS)
                        1.0.0.127.in-addr.arpa (PTR)
            0.0.10.in-addr.arpa
                Options:
                    allow-transfer: none 
                    allow-update: none 
                Resource Recs:
                        1.0.0.10.in-addr.arpa (PTR)
                        0.0.10.in-addr.arpa (SOA)
                        0.0.10.in-addr.arpa (NS)

Now that we have our records, let’s think of how to use them in the new server. In the above example, we list test.com as a zone. And in that zone we have an A record for test.test.com and a CNAME for testalias.test.com that points to test.test.com – but we don’t know where test.test.com resolves to. Each of those domains has a corresponding file that starts with db. followed by the name of the domain in the /Library/Server/named directory. So we can cat the test.com file as follows:

cat /Library/Server/named/db.test.com

test.com.       10800 IN SOA test.com. admin.test.com. (
2018033001
3600
900
1209600
86400)
     10800 IN NS test.test.com.
     10800 IN MX 0 test.test.com.
test.test.com.       10800 IN A 10.0.0.1
testalias.test.com.       10800 IN CNAME test.test.com.

Now we know the IP address that each record points to and can start building them out in other systems. If you only have 5-20 records, this is pretty quick and easy. If you have hundreds, then you’re in luck, as those db files per domain are portable between hosts. Some of the settings to look out for from macOS Server include:
  • Primary Zone: The DNS “Domain”. For example, www.krypted.com would likely have a primary zone of krypted.com.
  • Machine Record: An A record for a computer, or a record that tells DNS to resolve whatever name is indicated in the “machine” record to an IP address, whether the IP address is reachable or not.
  • Name Server: NS record, indicates the authoritative DNS server for each zone. If you only have one DNS server then this should be the server itself.
  • Reverse Zone: Zone that maps each name that IP addresses within the zone answer with. Reverse Zones are comprised of Reverse Mappings and each octal change in an IP scheme that has records mapped represents a new Reverse Zone.
  • Reverse Mapping: PTR record, or a record that indicates the name that should respond for a given IP address. These are automatically created for the first IP address listed in a Machine Record.
  • Alias Record: A CNAME, or a name that points to another name.
  • Service Record: Records that can hold special types of data that describe where to look for services for a given zone. For example, iCal can leverage service records so that users can just type the username and password during the setup process.
  • Mail Exchanger Record (aka MX record): Mail Exchanger, points to the IP address of the mail server for a given domain (aka Primary or Secondary Zone).
  • Secondary Zone: A read only copy of a zone that is copied from the server where it’s a Primary Zone when created and routinely through what is known as a Zone Transfer.
The settings for the domains are as follows:
  • allow-transfer Takes one or more address match list entry. Address match list entries consist of any of these forms: IP addresses, Subnets or Keywords.
  • allow-recursion Takes one or more address match list entry.
  • allow-update Takes one or more address match list entry.
  • allow-query Takes one or more address match list entry.
  • allow-query-cache Takes one or more address match list entry.
  • forwarders Takes one or more IP addresses, e.g. 10.1.1.1
  • directory Takes a directory path
  • tkey-gssapi-credential Takes a kerberos service principal
  • tkey-domain Takes a kerberos realm
  • update-policy Takes one complete update-policy entry where you can grant or deny various matched objects and specify the dentity of the user/machine that is allowed/disallowed to update.. You can also identify match-type (Type of match to be used in evaulating the entry) and match-name (Name used to match) as well as rr-types (Resource record types that can be updated)
Now, let’s get to setting up the new server. We’ll open the Synology and then click on Package Center. Then we’ll click All in the sidebar and search for DNS, as you can see below.

Click Install and the service will be installed on your NAS. Once installed, use the menu item in the upper left corner of the screen to bring up DNS Manager. Here, you can create your first zone. We’ll recreate test.com. To get started, click on Create and then Master Zone.

At the Master Zone screen, select Forward Zone if you’re creating a zone with a name or Reverse Zone if you’re creating a zone for IP addresses to resolve back to names (or PTR records). Since test.com is a name, we’ll select Forward Zone and then enter test.com in the “Domain name” field. Enter the IP address of the NAS in the “Master DNS server” field and leave the serial format as-is unless you have a good reason not to.

There are some options to secure connectivity to the service as well: 
  • Limit zone transfer: Restrict this option only to slave servers for each zone.
  • Limit source IP service: Restrict this option only to hosts that should be able to lookup records for the zone (which is usually everyone so this isn’t often used).
  • Enable slave zone notification: Identify all the slave servers so they get a notification about changes to zone files and can update their files based on those on the server.
  • Limit zone update: Only specify other servers that are allowed to update the zone files on your server.
Click OK when you’ve configured the zone as you’d like.

Double-click the zone to load a list of records and create new ones. 

Click Create to see a list of record types:

Record types include the following:
  • A Type: Resolve a name to an IPv4 address
  • AAAA Type: Resolve a name to an IPv6 address
  • CNAME: Resolve a name to a name
  • MX: Define the mail server for a domain
  • NS: Define DNS servers for a domain
  • SPF: Define what mail servers are allowed to send mail from a domain
  • SRV: Service records (e.g. the Active Directory or Exchange server for a domain)
  • TXT: Text records
  • CAA: Define the Certificate Authorities (CAs) for a domain
Click A Type to create that test.test.com record.

At the record screen, provide the hostname, along with the IP address that the name should resolve to. Notice that the TTL is a number of seconds. This is how many seconds before another DNS server expires their record. So when they cache them, they aren’t looking the records up against your server every time a client needs to resolve the address. I like the number provided, but when I’m about to move a service I’ll usually come back and reduce that a few days before the move. The nice thing about a high number of seconds before the next refresh though, is it can save on your bandwidth and on the bandwidth of the servers looking to yours to refresh their records. Once you’ve configured the record, click OK.

Click on Create and then CNAME. Enter the name that you’re pointing to another record (in this case CNAMEtest) in the Name: field and then the name that it’s pointing to (in this case test.test.com) in the Cononical Name: field. Click OK.

Now let’s get that MX record created. Click Create and select MX. Enter the name of the server you want to get mail (in this case test.test.com will be our mail server. Then provide a TTL (I usually use lower numbers for mail servers), the priority (if this is the only server I usually use 0 but if there’s a backup then I’ll use a number like 20), and finally the name of the domain. Click OK.

 
You’ll you can see all of your records. I know that Apple was always tinkering with the Server app to make DNS records display differently, trying to hide the complexity. But to be honest, I always considered this type of view (which is standard amongst most network appliances) to be much more logical. That might be because I’m just used to looking at db files back in the pre-GUI days. But it makes sense to me. 

Notice in the sidebar, you have an option for Resolution. This is if the server is going to be used to resolve addresses upstream. What are those upstream servers. This is where you configure them. Don’t enable this option if the DNS server is only used by external clients to resolve names hosted on the server. Do use this if there will be clients on your network attempting to resolve against your server.

Use the Views option to configure bind views. We’ll cover this at some point, but since this article is getting a bit long, let’s just say that this is where you configure different zone files for different subnets based on the source of the subnet. Useful if you want to use the same DNS server to host external and internal addressing, and you want the internals to point to LAN addresses and the externals to point to WAN addresses.

Finally, if this DNS server will be providing services to external hosts, then point port 53 to the new server and set the name server record to the IP address on the WAN with the registrar.

March 31st, 2018

Posted In: Mac OS X Server, Synology

Tags: , , , , , , , ,