import re

string = """
192.168.1.1
USER_NAME=admin
PASSWORD=admin123

192.168.1.2
USER_NAME=user
PASSWORD=user123
"""

regex = re.compile(r"""
	^
	(?P<ip>\d+\.\d+\.\d+\.\d+)[\n\r]
	USER_NAME=(?P<user>.+)[\r\n]
	PASSWORD=(?P<password>.+)
	""", re.MULTILINE | re.VERBOSE)

users = {match.group('ip'):{'USER_NAME': match.group('user'), 'PASSWORD': match.group('password')} \
			for match in regex.finditer(string)}

print(users)