Linux – Adding custom dns entries for name resolution in the local network

if your happy to use a production domain then you could run DNSMasq on your internal network and have all your servers use it as there caching resolver

this has 2 benefits

1. Speed Up DNS resolution accross your internal network due to caching results locally
2. Ability to use DNSMasq's alias config command to change DNS results on the fly

to give a bit more info about point 2 above from the dnsmasq example config:

# If you want to fix up DNS results from upstream servers, use the
# alias option. This only works for IPv4.
# This alias makes a result of 1.2.3.4 appear as 5.6.7.8
#alias=1.2.3.4,5.6.7.8
# and this maps 1.2.3.x to 5.6.7.x
#alias=1.2.3.0,5.6.7.0,255.255.255.0
# and this maps 192.168.0.10->192.168.0.40 to 10.0.0.10->10.0.0.40
#alias=192.168.0.10-192.168.0.40,10.0.0.0,255.255.255.0

basically this means that if you ever do a DNS lookup for an address that normally returns IP 1.2.3.4 in DNS it will rewrite it on the fly to return 5.6.7.8

replace that for your external IP to internal IP mapping and then your on to a winner

the alternative if you want to use an "internal only zone" would again be to use DNSmasq and the hosts file on the dnsmasq server to define your internal DNS records, dnsmasq uses your hosts file and its configured external resolvers to return DNS results to its clients (with hosts file taking priority by default) just like if you were to add the records to the hosts file on each box but only having to do it in a single location

Just remember to reload/restart dnsmasq when you make changes to the hosts file on that machine

Apparently nblookup does not work with reverse IP -> hostname lookups. I started capturing packets with MS Network Monitor to see how netstat was resolving the name and learned something new. Apparently it will revert to NetBIOS lookups if DNS fails.

Another important thing to note, I ran into trouble when troubleshooting this because my local machine is Windows 7. Another method Windows 7 uses is called LLMNR. So, if DNS fails it will try to perform a LLMNR lookup. LLMNR isn't available in Windows Server 2003.

Resolution order:

1. DNS
   a. Resolver Cache (Hosts File + Cached DNS Queries) (ipconfig /displaydns)
   b. DNS Server Query (ipconfig /all to see DNS Servers that will be queried, nslookup to attempt queries)
   
2. LLMNR (Windows Vista/7/8, Server 2008)
   a. LLMNR Cache
   b. LLMNR Multicast Query
   
3. NetBIOS (Order and methods depend on NetBIOS Node Type -- find type by: ipconfig /all | findstr "Node Type"
   a. WINS Servers (h node, m node, p node)
   b. LMHosts File
   c. Broadcast (h node, m node, b node)
   
   

Here is a fantastic youtube video on the different resolution techniques: https://www.youtube.com/watch?v=gzqjeds8gDg and there is a great MSDN TechNet Article on name resolution, search for "Link-Local Multicast Name Resolution: The Cable Guy".