How to Setup DNS Forwarding for Individual URL in Linux Bind

Learn how to setup DNS forwarding for individual URL in Linux bind to route the queries to the internal load balancer instead of the internet.

DNS forwarding is a technique to forward DNS queries to another DNS server, usually an upstream server, for resolution. DNS forwarding can be used to improve performance, security, or reliability of DNS services. In this article, you will learn how to setup DNS forwarding for individual URL in Linux bind, a popular DNS server software. You will also learn how to troubleshoot the DNS forwarding and verify the results.

Table of Contents

What is DNS Forwarding and Why Use It?
How to Setup DNS Forwarding for Individual URL in Linux Bind
Frequently Asked Questions (FAQs)
Summary

What is DNS Forwarding and Why Use It?

DNS forwarding is a process of sending DNS queries from one DNS server to another DNS server for resolution. The DNS server that forwards the queries is called a forwarder, and the DNS server that receives and answers the queries is called a resolver. The resolver can be either a recursive resolver that contacts other DNS servers to find the answer, or an authoritative resolver that has the answer in its own zone files.

DNS forwarding can be used for various purposes, such as:

Improving performance: By forwarding the queries to a resolver that is closer to the authoritative servers or has a better cache, the forwarder can reduce the latency and network traffic for the queries.
Improving security: By forwarding the queries to a resolver that has security features such as DNSSEC validation, DNS filtering, or DNS firewall, the forwarder can protect its clients from DNS attacks or malicious domains.
Improving reliability: By forwarding the queries to a resolver that has redundancy, load balancing, or failover mechanisms, the forwarder can ensure the availability and consistency of the DNS service.

DNS forwarding can be configured in different ways, such as:

Global forwarding: The forwarder forwards all the queries that it cannot answer locally to the resolver.
Conditional forwarding: The forwarder forwards only the queries for a specific domain or zone to the resolver.
Selective forwarding: The forwarder forwards only the queries for a specific URL or record to the resolver.

In this article, you will learn how to setup selective forwarding for individual URL in Linux bind.

How to Setup DNS Forwarding for Individual URL in Linux Bind

To setup DNS forwarding for individual URL in Linux bind, you need to follow these steps:

Install and configure bind as a caching or forwarding DNS server on Ubuntu 14.04. You can also use other Linux distributions or versions, as long as they have bind installed and running.
Create a zone file for the URL that you want to forward. For example, if you want to forward the queries for sosc-held.clc.tiger23.com to the internal load balancer, you need to create a zone file named sosc-held.clc.tiger23.com.zone in the /etc/bind directory. The zone file should contain the following records:
```
$TTL 86400
@ IN SOA ns1.clc.tiger23.com. admin.clc.tiger23.com. (
    2021090101 ; serial
    7200       ; refresh
    3600       ; retry
    1209600    ; expire
    86400 )    ; minimum
@ IN NS ns1.clc.tiger23.com.
@ IN A 192.168.0.10 ; IP address of the internal load balancer
```

Edit the named.conf.local file in the /etc/bind directory and add the following zone statement:

zone "sosc-held.clc.tiger23.com" {
    type master;
    file "/etc/bind/sosc-held.clc.tiger23.com.zone";
};

Restart the bind service to apply the changes:
```
$ sudo systemctl restart bind9
```
Test the DNS forwarding by using the nslookup command from the client machine. For example, if the client machine has the IP address 192.168.0.100, you can run the following command:
```
$ nslookup sosc-held.clc.tiger23.com 192.168.0.1
Server:         192.168.0.1
Address:        192.168.0.1#53

Name:   sosc-held.clc.tiger23.com
Address: 192.168.0.10
```
The output shows that the query for sosc-held.clc.tiger23.com is resolved to the IP address of the internal load balancer, which is 192.168.0.10. This means that the DNS forwarding is working as expected.

Frequently Asked Questions (FAQs)

Question: How can I troubleshoot the DNS forwarding if it is not working?

Answer: If the DNS forwarding is not working, you can use the following steps to troubleshoot the problem:

Check the syntax and spelling of the zone file and the named.conf.local file. You can use the named-checkzone and named-checkconf commands to verify the files. For example:

$ sudo named-checkzone sosc-held.clc.tiger23.com /etc/bind/sosc-held.clc.tiger23.com.zone
zone sosc-held.clc.tiger23.com/IN: loaded serial 2021090101
OK
$ sudo named-checkconf /etc/bind/named.conf.local

Check the permissions and ownership of the zone file and the named.conf.local file. They should be readable by the bind user and group. You can use the ls -l command to check the permissions and ownership. For example:

$ ls -l /etc/bind/sosc-held.clc.tiger23.com.zone
-rw-r--r-- 1 bind bind 221 Sep  1 10:15 /etc/bind/sosc-held.clc.tiger23.com.zone
$ ls -l /etc/bind/named.conf.local
-rw-r--r-- 1 bind bind 237 Sep  1 10:16 /etc/bind/named.conf.local

Check the logs of the bind service for any errors or warnings. You can use the journalctl command to view the logs. For example:
```
$ sudo journalctl -u bind9
```
Check the network connectivity and firewall rules between the client machine, the DNS server, and the internal load balancer. You can use the ping, traceroute, and iptables commands to check the network connectivity and firewall rules. For example:
```
$ ping 192.168.0.1
$ traceroute 192.168.0.10
$ sudo iptables -L -n
```

Question: How can I setup DNS forwarding for a specific domain or zone instead of an individual URL?

Answer: If you want to setup DNS forwarding for a specific domain or zone instead of an individual URL, you can use the conditional forwarding option in the named.conf.options file. For example, if you want to forward the queries for clc.tiger23.com and its subdomains to the internal load balancer, you can add the following option:

options {
    ...
    forwarders {
        8.8.8.8;
        8.8.4.4;
    };
    forward only;
    ...
};

zone "clc.tiger23.com" {
    type forward;
    forwarders { 192.168.0.10; };
};

This will forward all the queries for clc.tiger23.com and its subdomains to the internal load balancer, and all the other queries to the global forwarders.

Summary

In this article, you learned how to setup DNS forwarding for individual URL in Linux bind. You also learned what is DNS forwarding and why use it, and how to troubleshoot the DNS forwarding if it is not working. You also learned how to setup DNS forwarding for a specific domain or zone instead of an individual URL.

Disclaimer: This article is for informational purposes only and does not constitute professional advice. The information and instructions in this article are based on the current version of Linux bind as of the date of publication. The information and instructions may change or become outdated in the future. You should always consult the official documentation and support resources of Linux bind before applying any changes or updates to your system. The author and publisher of this article are not responsible for any errors, omissions, damages, or losses that may result from following the information and instructions in this article.