Unless the firmware vendor has modified the function which checks the proxy bypass list, specifying IP address ranges in the list is not possible — all entries are compared like domain names. Also the
* wildcard is not supported, but is implied at the start of the domain name, as answered here (still valid even for JB).
So, if you want to use the builtin proxy support, you either need to list all required IP addresses explicitly, or, if your LAN has a DNS server, and all local servers are under some domain (
server.local), add that domain (
local for my examples) into the proxy bypass list, then access local servers using DNS names instead of raw IP addresses.
Alternatively, if you have a rooted phone, you can install a third-party proxy app such as ProxyDroid or Autoproxy; they should be more configurable than the builtin proxy support code.