BIND: Konfigurasi sebagai private DNS
Install BIND
install BIND
sudo su apt update apt install bind9 bind9utils bind9-doc
Setup hanya untuk IPv4 (-4) jika dibutuhkan
vi /etc/default/bind9
Tambahkan (-4)
OPTIONS="-4 -u bind"
Konfigurasi Primary DNS Server
Edit
sudo vi /etc/bind/named.conf.options
Jika dibutuhkan kita bisa menambahkan trusted client
acl "trusted" {
10.128.10.11; # ns1 - can be set to localhost
10.128.20.12; # ns2
10.128.100.101; # host1
10.128.200.102; # host2
};
Ubah ns1 IP address yang benar, misalnya,
options {
directory "/var/cache/bind";
recursion yes; # enables resursive queries
allow-recursion { trusted; }; # allows recursive queries from "trusted" clients
listen-on { 10.128.10.11; }; # ns1 private IP address - listen on private network only
allow-transfer { none; }; # disable zone transfers by default
forwarders {
8.8.8.8;
8.8.4.4;
};
...
};
Konfigurasi Local File
Edit
sudo vi /etc/bind/named.conf.local
Di file ini kita bisa tambahkan forward dan revese zone dari sebuah domain, contoh
zone "nyc3.example.com" {
type master;
file "/etc/bind/zones/db.nyc3.example.com"; # zone file path
allow-transfer { 10.128.20.12; }; # ns2 private IP address - secondary
};
Asumsi private subnet 10.128.0.0/16, reverse zone- adalah,
zone "128.10.in-addr.arpa" {
type master;
file "/etc/bind/zones/db.10.128"; # 10.128.0.0/16 subnet
allow-transfer { 10.128.20.12; }; # ns2 private IP address - secondary
};
Buat Forward Zone File
Buat dan edit
sudo mkdir /etc/bind/zones cd /etc/bind/zones sudo cp ../db.local ./db.nyc3.example.com sudo vi /etc/bind/zones/db.nyc3.example.com
Isi awalnya kira-kira
$TTL 604800
@ IN SOA localhost. root.localhost. (
2 ; Serial
604800 ; Refresh
86400 ; Retry
2419200 ; Expire
604800 ) ; Negative Cache TTL
;
@ IN NS localhost. ; delete this line
@ IN A 127.0.0.1 ; delete this line
@ IN AAAA ::1 ; delete this line
Dapat kita ubah menjadi, misalnya,
$TTL 604800
@ IN SOA ns1.nyc3.example.com. admin.nyc3.example.com. (
3 ; Serial
604800 ; Refresh
86400 ; Retry
2419200 ; Expire
604800 ) ; Negative Cache TTL
;
; name servers - NS records
IN NS ns1.nyc3.example.com.
IN NS ns2.nyc3.example.com.
; name servers - A records
ns1.nyc3.example.com. IN A 10.128.10.11
ns2.nyc3.example.com. IN A 10.128.20.12
; 10.128.0.0/16 - A records
host1.nyc3.example.com. IN A 10.128.100.101
host2.nyc3.example.com. IN A 10.128.200.102
Create Reverse Zone File(s)
Reverse zone file are where we define DNS PTR records for reverse DNS lookups. That is, when the DNS receives a query by IP address, "10.128.100.101" for example, it will look in the reverse zone file(s) to resolve the corresponding FQDN, "host1.nyc3.example.com" in this case.
On ns1, for each reverse zone specified in the named.conf.local file, create a reverse zone file. We will base our reverse zone file(s) on the sample db.127 zone file. Copy it to the proper location with the following commands (substituting the destination filename so it matches your reverse zone definition):
cd /etc/bind/zones sudo cp ../db.127 ./db.10.128
Edit the reverse zone file that corresponds to the reverse zone(s) defined in named.conf.local:
sudo vi /etc/bind/zones/db.10.128
Initially, it will look something like the following: /etc/bind/zones/db.10.128 — original
$TTL 604800 @ IN SOA localhost. root.localhost. (
1 ; Serial
604800 ; Refresh
86400 ; Retry
2419200 ; Expire
604800 ) ; Negative Cache TTL
@ IN NS localhost. ; delete this line 1.0.0 IN PTR localhost. ; delete this line
In the same manner as the forward zone file, you will want to edit the SOA record and increment the serial value. It should look something like this: /etc/bind/zones/db.10.128 — updated 1 of 3
@ IN SOA ns1.nyc3.example.com. admin.nyc3.example.com. (
3 ; Serial
Now delete the two records at the end of the file (after the SOA record). If you're not sure which lines to delete, they are marked with a "delete this line" comment above.
At the end of the file, add your nameserver records with the following lines (replace the names with your own). Note that the second column specifies that these are "NS" records: /etc/bind/zones/db.10.128 — updated 2 of 3
- name servers - NS records
IN NS ns1.nyc3.example.com.
IN NS ns2.nyc3.example.com.
Then add PTR records for all of your servers whose IP addresses are on the subnet of the zone file that you are editing. In our example, this includes all of our hosts because they are all on the 10.128.0.0/16 subnet. Note that the first column consists of the last two octets of your servers' private IP addresses in reversed order. Be sure to substitute names and private IP addresses to match your servers: /etc/bind/zones/db.10.128 — updated 3 of 3
- PTR Records
11.10 IN PTR ns1.nyc3.example.com. ; 10.128.10.11 12.20 IN PTR ns2.nyc3.example.com. ; 10.128.20.12 101.100 IN PTR host1.nyc3.example.com. ; 10.128.100.101 102.200 IN PTR host2.nyc3.example.com. ; 10.128.200.102
Save and exit the reverse zone file (repeat this section if you need to add more reverse zone files).
Our final example reverse zone file looks like the following: /etc/bind/zones/db.10.128 — updated
$TTL 604800 @ IN SOA nyc3.example.com. admin.nyc3.example.com. (
3 ; Serial
604800 ; Refresh
86400 ; Retry
2419200 ; Expire
604800 ) ; Negative Cache TTL
- name servers
IN NS ns1.nyc3.example.com.
IN NS ns2.nyc3.example.com.
- PTR Records
11.10 IN PTR ns1.nyc3.example.com. ; 10.128.10.11 12.20 IN PTR ns2.nyc3.example.com. ; 10.128.20.12 101.100 IN PTR host1.nyc3.example.com. ; 10.128.100.101 102.200 IN PTR host2.nyc3.example.com. ; 10.128.200.102
Check BIND Configuration Syntax
Run the following command to check the syntax of the named.conf* files:
sudo named-checkconf
If your named configuration files have no syntax errors, you will return to your shell prompt and see no error messages. If there are problems with your configuration files, review the error message and the Configure Primary DNS Server section, then try named-checkconf again.
The named-checkzone command can be used to check the correctness of your zone files. Its first argument specifies a zone name, and the second argument specifies the corresponding zone file, which are both defined in named.conf.local.
For example, to check the "nyc3.example.com" forward zone configuration, run the following command (change the names to match your forward zone and file):
sudo named-checkzone nyc3.example.com db.nyc3.example.com
And to check the "128.10.in-addr.arpa" reverse zone configuration, run the following command (change the numbers to match your reverse zone and file):
sudo named-checkzone 128.10.in-addr.arpa /etc/bind/zones/db.10.128
When all of your configuration and zone files have no errors in them, you should be ready to restart the BIND service. Restart BIND
Restart BIND:
sudo service bind9 restart
Your primary DNS server is now setup and ready to respond to DNS queries. Let's move on to creating the secondary DNS server. Configure Secondary DNS Server
In most environments, it is a good idea to set up a secondary DNS server that will respond to requests if the primary becomes unavailable. Luckily, the secondary DNS server is much easier to configure.
On ns2, edit the named.conf.options file:
sudo vi /etc/bind/named.conf.options
At the top of the file, add the ACL with the private IP addresses of all of your trusted servers: /etc/bind/named.conf.options — updated 1 of 2 (secondary)
acl "trusted" {
10.128.10.11; # ns1
10.128.20.12; # ns2 - can be set to localhost
10.128.100.101; # host1
10.128.200.102; # host2
};
Below the directory directive, add the following lines: /etc/bind/named.conf.options — updated 2 of 2 (secondary)
recursion yes;
allow-recursion { trusted; };
listen-on { 10.128.20.12; }; # ns2 private IP address
allow-transfer { none; }; # disable zone transfers by default
forwarders {
8.8.8.8;
8.8.4.4;
};
Save and exit named.conf.options. This file should look exactly like ns1's named.conf.options file except it should be configured to listen on ns2's private IP address.
Now edit the named.conf.local file:
sudo vi /etc/bind/named.conf.local
Define slave zones that correspond to the master zones on the primary DNS server. Note that the type is "slave", the file does not contain a path, and there is a masters directive which should be set to the primary DNS server's private IP. If you defined multiple reverse zones in the primary DNS server, make sure to add them all here: /etc/bind/named.conf.local — updated (secondary)
zone "nyc3.example.com" {
type slave;
file "slaves/db.nyc3.example.com";
masters { 10.128.10.11; }; # ns1 private IP
};
zone "128.10.in-addr.arpa" {
type slave;
file "slaves/db.10.128";
masters { 10.128.10.11; }; # ns1 private IP
};
Now save and exit named.conf.local.
Run the following command to check the validity of your configuration files:
sudo named-checkconf
Once that checks out, restart bind
sudo service bind9 restart
Now you have primary and secondary DNS servers for private network name and IP address resolution. Now you must configure your servers to use your private DNS servers. Configure DNS Clients
Before all of your servers in the "trusted" ACL can query your DNS servers, you must configure each of them to use ns1 and ns2 as nameservers. This process varies depending on OS, but for most Linux distributions it involves adding your name servers to the /etc/resolv.conf file. Ubuntu Clients
On Ubuntu and Debian Linux VPS, you can edit the head file, which is prepended to resolv.conf on boot:
sudo vi /etc/resolvconf/resolv.conf.d/head
Add the following lines to the file (substitute your private domain, and ns1 and ns2 private IP addresses): /etc/resolvconf/resolv.conf.d/head
search nyc3.example.com # your private domain nameserver 10.128.10.11 # ns1 private IP address nameserver 10.128.20.12 # ns2 private IP address
Now run resolvconf to generate a new resolv.conf file:
sudo resolvconf -u
Your client is now configured to use your DNS servers. CentOS Clients
On CentOS, RedHat, and Fedora Linux VPS, simply edit the resolv.conf file:
sudo vi /etc/resolv.conf
Then add the following lines to the TOP of the file (substitute your private domain, and ns1 and ns2 private IP addresses): /etc/resolv.conf
search nyc3.example.com # your private domain nameserver 10.128.10.11 # ns1 private IP address nameserver 10.128.20.12 # ns2 private IP address
Now save and exit. Your client is now configured to use your DNS servers. Test Clients
Use nslookup to test if your clients can query your name servers. You should be able to do this on all of the clients that you have configured and are in the "trusted" ACL. Forward Lookup
For example, we can perform a forward lookup to retrieve the IP address of host1.nyc3.example.com by running the following command:
nslookup host1
Querying "host1" expands to "host1.nyc3.example.com because of the search option is set to your private subdomain, and DNS queries will attempt to look on that subdomain before looking for the host elsewhere. The output of the command above would look like the following:
Output: Server: 10.128.10.11 Address: 10.128.10.11#53
Name: host1.nyc3.example.com Address: 10.128.100.101
Reverse Lookup
To test the reverse lookup, query the DNS server with host1's private IP address:
nslookup 10.128.100.101
You should see output that looks like the following:
Output: Server: 10.128.10.11 Address: 10.128.10.11#53
11.10.128.10.in-addr.arpa name = host1.nyc3.example.com.
If all of the names and IP addresses resolve to the correct values, that means that your zone files are configured properly. If you receive unexpected values, be sure to review the zone files on your primary DNS server (e.g. db.nyc3.example.com and db.10.128).
Congratulations! Your internal DNS servers are now set up properly! Now we will cover maintaining your zone records. Maintaining DNS Records
Now that you have a working internal DNS, you need to maintain your DNS records so they accurately reflect your server environment. Adding Host to DNS
Whenever you add a host to your environment (in the same datacenter), you will want to add it to DNS. Here is a list of steps that you need to take: Primary Nameserver
Forward zone file: Add an "A" record for the new host, increment the value of "Serial" Reverse zone file: Add a "PTR" record for the new host, increment the value of "Serial" Add your new host's private IP address to the "trusted" ACL (named.conf.options)
Then reload BIND:
sudo service bind9 reload
Secondary Nameserver
Add your new host's private IP address to the "trusted" ACL (named.conf.options)
Then reload BIND:
sudo service bind9 reload
Configure New Host to Use Your DNS
Configure resolv.conf to use your DNS servers Test using nslookup
Removing Host from DNS
If you remove a host from your environment or want to just take it out of DNS, just remove all the things that were added when you added the server to DNS (i.e. the reverse of the steps above). Conclusion
Now you may refer to your servers' private network interfaces by name, rather than by IP address. This makes configuration of services and applications easier because you no longer have to remember the private IP addresses, and the files will be easier to read and understand. Also, now you can change your configurations to point to a new servers in a single place, your primary DNS server, instead of having to edit a variety of distributed configuration files, which eases maintenance.
Once you have your internal DNS set up, and your configuration files are using private FQDNs to specify network connections, it is critical that your DNS servers are properly maintained. If they both become unavailable, your services and applications that rely on them will cease to function properly. This is why it is recommended to set up your DNS with at least one secondary server, and to maintain working backups of all of them.