Bind Operations - Set Up DNS Server

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Overview

This is a step by step guide on installing and configuring a bind DNS server. We needed it during the deployment of an OpenShift environment. During this procedure, we will create a new "openshift35.local" zone file and all OpenShift hosts will get names within the "*.openshift35.local" DNS domain. Additional zone files/local domains can be added later.

Relevance

  • RHEL 7.1
  • Centos 7.3

Binary Installation

Intall bind binaries: 

yum install bind* -y

DO NOT yum remove bind*, it will remove dhclient and related libraries, and that might render your host inoperable.

Starting and Stopping the Server

Installing binaries will deploy a bind server with a basic configuration that can be started and stopped.

Starting the Server

You can start the server right away, it should start fine. See Troubleshooting the Server. 

systemctl start named

Stopping the Server

systemctl stop named

Troubleshooting the Server

systemctl status: 

systemctl status named

journalctl: 

journalctl -u named

Log file: 

/var/named/data/named.run

Edit /etc/named.conf

/etc/named.conf is the main configuration file.

Use the default and modify the following:

listen-on

Specifies the IPv4 network interface on which to listen for queries.

On a DNS server that acts as a gateway, you can use this option to answer queries originating from a single network only. All IPv4 interfaces are used by default. 

options {

        ...

        listen-on port 53 { any; };

        ...

}

Alternatively, to specify a single interface: 

        listen-on port 53 { 172.30.0.3; };

listen-on-v6

Specifies the IPv6 network interface on which to listen for queries.

On a DNS server that also acts as a gateway, you can use this option to answer queries originating from a single network only. All IPv6 interfaces are used by default. 

options {

        ...

        listen-on-v6 port 53 { any; };

        ...

}

allow-query

Specifies which hosts are allowed to query the nameserver for authoritative resource records.

It accepts an access control list, a collection of IP addresses, or networks in the CIDR notation. All hosts are allowed by default. 

options {

        ...

        allow-query     { any; };

        ...

}

Adding a Zone

Add a zone in /etc/named.conf, as follows. Conventionally, I place it between the zone "." and include: 

...
zone "." IN {
        type hint;
        file "named.ca";
};

zone "openshift.local" IN {
        type master;
        file "openshift.local.zone";
};

include "/etc/named.rfc1912.zones";
...

The zone file path specified after "file" is relative to /var/named.

Start with named.localhost as a model: 

cd /var/named
cp named.localhost openshift.local.zone

Make sure the file has the same ownership as the rest of the files in the directory: 

chown root:named openshift.local.zone

Zone File

/var/named/openshift.local.zone: 

$TTL 3600
@                       IN SOA  openshift.local. root (
                                        2015092101      ; serial
                                        3600            ; refresh
                                        15M             ; retry
                                        1W              ; expire
                                        1D )            ; minimum
                        IN NS   localhost
localhost               IN A    127.0.0.1
ns                      IN A    172.20.2.10
openshift-master1       IN A    172.20.2.1
openshift-node1         IN A    172.20.2.2
openshift-node2         IN A    172.20.2.3

PTR (Inverse Record) File

TODO: not tested.

/var/named/openshift.local.rzone: 

$TTL 3600
@			IN SOA	openshift.local. root.openshift.local. (
					2015092101	; serial
					3600		; refresh
					15M		; retry
					1W		; expire
					1D )		; minimum
			IN NS	localhost.
172.20.2.1		IN PTR 	openshift-master1.openshift.local.
172.20.2.2		IN PTR  openshift-node1.openshift.local.

Make sure the file has the same ownership as the rest of the files in the directory: 

chown root:named openshift.local.rzone

I think the reverse resolution is not fully enabled until I add something like the following in /etc/named.conf: 

zone"0.168.192.in-addr.arpa" IN {
type master;
file "reverse.linuxzadmin";
allow-update { none; };
};

Verify Configuration Files

named-checkconf /etc/named.conf 

named-checkzone  <zone-name> <zone-file>
named-checkzone  openshift.local.zone /var/named/openshift.local.zone

Configure iptables

Add the following rules to your iptables configuration: 

...
iptables -A INPUT -p tcp -m state --state NEW -m tcp --dport 53 -j ACCEPT
iptables -A INPUT -p udp -m state --state NEW -m udp --dport 53 -j ACCEPT
...

For more details on the iptables configuration, see

iptables IPv4 Base Configuration

Make sure the correct rules are in place with iptables -F:

Also see

ping and ssh succeed but telnet fails

Configuring Recursive Resolution

If a name cannot be resolved by the current bind server, the query is forwarded to other DNS servers.

Which one are those? How are those configured?

For a standard bind installation, I did not need to do anything, the mechanism worked by default.

Starting at Boot

systemctl enable named

Test: 

systemctl is-enabled named
enabled

Configure The Local DNS Resolver

Same as configuring clients on other machines in the network. See

Set Up DNS Client

Configure DNS Resolver on Other Hosts

Set Up DNS Client

Reboot and Test

Local Tests

Assuming that the name of the name server is "ns.openshift.local", and "openshift-master1.openshift.local" is a valid host in domain, after reboot, the following must be successful: 

# nslookup ns
Server:		172.20.2.10
Address:	172.20.2.10#53

Name:	ns.openshift.local
Address: 172.20.2.10

# nslookup ns.openshift.local
Server:		172.20.2.10
Address:	172.20.2.10#53

Name:	ns.openshift.local
Address: 172.20.2.10

# nslookup openshift-master1
Server:		172.20.2.10
Address:	172.20.2.10#53

Name:	openshift-master1.openshift.local
Address: 172.20.2.1

# nslookup openshift-master1.openshift.local
Server:		172.20.2.10
Address:	172.20.2.10#53

Name:	openshift-master1.openshift.local
Address: 172.20.2.1

Also a random (but valid) name must be resolved 

# nslookup www.cnn.com
Server:		172.20.2.10
Address:	172.20.2.10#53

Non-authoritative answer:
www.cnn.com	canonical name = turner.map.fastly.net.
Name:	turner.map.fastly.net
Address: 23.235.47.73

Remote Tests

Adding a New Host to the Zone File

Go to the corresponding zone file (example if the domain is openshift.local, the zone file is /var/named/openshift.local.zone) 

...
master31-1              IN A    172.20.2.11

Also modify the inverse record file /var/named/openshift.local.rzone (if exists) 

172.20.2.11		IN PTR  master31-1.openshift.local.

Then reboot the name server.

After reboot, run nslookup from the name server itself, an old host and the newly setup host: 

[openshift@ns ~]$ nslookup master31-1.openshift.local
Server:		172.20.2.10
Address:	172.20.2.10#53

Name:	master31-1.openshift.local
Address: 172.20.2.11
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