#! /usr/bin/perl

use strict;
use warnings;
use Win32::Service;
use Win32::Registry;

my (%ipconf);

#Change IP to DHCP Addresses and Proxy-xx:Port to Proxy Address 
#[n/y] Start services or not.
%ipconf = (     "196.10.xx.xx"     => ["Proxy-ONE:8080", "n"], 
        "172.21.xx.xx"    => ["PROXY-TWO:80", "y"]);

#Check the current IP Address
$::HKEY_LOCAL_MACHINE->Open("SYSTEM\\CurrentControlSet\\Services\\{199
+1FDD6-910A-44EA-B6A4-FDA4E1165BC7}\\Parameters\\Tcpip", my $ip) or di
+e "Can't read IP: $^E";

$ip->QueryValueEx("DhcpIPAddress", my $type, my $value) or die "No IP 
+Address available: $^E";
print "Your IP Address is: $value\n";

#If Address is Work
if (exists($ipconf{$value})) {
    if (&SetProxy($ipconf{$value}->[0])) {
        print " - Successful\n";
    } else {
        print " - Failed!\n";
        print "$^E\n";
    }    
} else {
    print "IP $value not found!\n";
}

if ($ipconf{$value}->[1] eq "y") {
    if (&StartSvc()) {
        print " - Successful\n";
    } else {
        print " - Failed!\n";
        print "$^E\n";
    }
}

$ip->Close;

######################################################################
+##################
##
##        SUB ROUTINES
##
######################################################################
+##################

#Set Proxy value in Win32 Registry
sub SetProxy
{
    my $proxy = $_[0];
    my $rc = 1;
    my $type = REG_SZ;
    my ($reserved, $proxy_str);
    print "Setting Proxy for $value to $proxy";
    if ($::HKEY_CURRENT_USER->Open("Software\\Microsoft\\Windows\\Curr
+entVersion\\Internet Settings", $proxy_str)) {
        unless ($proxy_str->SetValueEx("ProxyServer", $reserved, $type
+, $proxy)) { $rc = 0; }
    } else {
        $rc = 0;
    }
    $proxy_str->Close;
    return($rc);
}

#Start Services.
sub StartSvc
{
    my $rc = 1;
    my (%list);
    my @svc_list = ("MSSQLSERVER");
    foreach my $svc (@svc_list) {
        print "Starting $svc";
        if (Win32::Service::GetServices($ENV{COMPUTERNAME}, \%list)) {
            unless (Win32::Service::StartService($ENV{COMPUTERNAME}, $
+list{"$svc"})) { $rc = 0; }
        } else {
            $rc = 0;
        }    
    }
    return ($rc);
}
[download]

Anyway the above code is a starting point for checking your local ip address and changing the registry to the corresponding proxy address.

Update: Code Changed to add the starting of services based on what you need to run on different networks.