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Brendan Abel
Asked: 2017-02-22 16:27:19 +0800 CST

How to set up DNS when connecting to two networks?

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I have a linux machine with two network interfaces. They are both connected to local networks -- one is 192.168.*.*, the other is 10.*.*.*.

The 192.168.*.* network is completely private and does not have internet access. The 10.*.*.* network does have internet access.

Currently, I can do external ping's and the names will resolve

ping google.com

However, when I try to ping a machine name on the 192.168.*.* network, the name will not resolve

ping computer-name
ping computer-name.domain
ping computer-name.domain.local

If I specify an IP address, it will resolve

ping 192.168.x.x

How can I set up DNS settings so that the machine names on the private local network will resolve, but I can still resolve external addresses?

I am using Centos6.

linux centos domain-name-system centos6

2 Answers

  1. In situations like this you usually need to setup a DNS resolver that will forward to various upstream DNS servers based on the namespace. You can do this with DNSMasq, Bind and other DNS servers.

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  2. I was able to get this working by modifying my /etc/resolv.conf file

    domain privatedomain
search privatedomain publicdomain.com
nameserver 192.168.10.15
nameserver 10.10.1.15

    The privatedomain is the local 192.168.*.* network domain name. The publicdomain.com is the domain name for the 10.*.*.* network with internet access.

    It can now resolve all these requests correctly

    ping computer.privatedomain
ping computer
ping computer2.publicdomain.com
ping google.com

    The only downside to this is that when I try to resolve a name that isn't reachable from the private domain, there is a noticeable delay. For example:

    ping google.com

    I imagine it's because it's first attempting to resolve the name via the first nameserver on the privatedomain, which will eventually timeout, and then goes to the second nameserver which is able to resolve it.

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