import re

a = (None, None)
b = (None, None)
with open('1.txt', 'r', encoding='utf-8') as f:
    for i, item in enumerate(f):
        if re.search(r"interface\s\S*", item):
            a = (re.search(r"interface\s\S*", item), i)

        if re.search(r"ip\saddress\s\S*\s\S*", item):
            b = (re.search(r"ip\saddress\s\S*\s\S*", item), i)

        if a[0] is not None and b[0] is not None and b[1] > a[1]:
            print(a[0].group(0), b[0].group(0))
            a = (None, None)
            b = (None, None)