Some time ago I used to remember IPs on my home and work network but these days I rely much more on dns and dhcp reservation for this tasks. This has the advantage that I can easy move a service, say git.example.com to a new server.
At home I switched (at least for a while) from a dedicated Debian router/gateway box to a router running Tomato. Suddenly subdomains pointing to private IP addresses were no longer resolved. Turns out the DNS rebinding protection is at fault. Now you could easily just disable it but this is not the secure way to fix a problem. You can actually white list domains to allow private IPs on subdomains.
Go to Advanced => DHCP / DNS Server (LAN)
Don’t uncheck _“Prevent DNS-rebind attacks” _as this will leave you vulnerable to this attack. Instead add the following to the Dnsmasq Custom configuration
Where domain1.com, domain2.com, etc. are the domains for which you want to allow subdomains that resolve to private IPs.