unexpected output while parsing file

[killerrex]

The problem is that you have more entries with "svc:1" than with "@ttml" but zip is hidding you this as it will stop when the shortest iterable is empty.

One solution can be to obtain directly the mapping as a dictionary:

import re

macdn = {}

with open('pppoe.txt','r') as f:
    dn = None
    for line in f:
        if '@ttml' in line:
            dn = re.findall(r'\d{10}',line)[0]

        if 'svc:1' in line and dn is not None:
            mac = re.findall(r'mac:[a-fA-F0-9]{2}[:][a-fA-AF0-9]{2}[:][a-fA-F0-9]{2}[:][a-fA-F0-9]{2}[:][a-fA-F0-9]{2}[:][a-fA-F0-9]{2}',line)
            
            if dn in macdn:
                macdn[dn].extend(mac)
            else:
                macdn[dn] = list(mac)
            dn = None

for dn in macdn:
    print('{} {}'.format(dn, macdn[dn]))

This allows for several macs with same dns. You can invert the logic easily to obtain a dictionary for one mac with several dns)

If you need to keep the 2 list format for something the same idea works: do not append to the lists until you have a valid dn:

import re

dnlist = []
maclist = []
 
with open('pppoe.txt','r') as f:
    dn = None
    for line in f:
        if '@ttml' in line:
            dn = re.findall(r'\d{10}',line)

        if 'svc:1' in line and dn is not None:
            mac = re.findall(r'mac:[a-fA-F0-9]{2}[:][a-fA-AF0-9]{2}[:][a-fA-F0-9]{2}[:][a-fA-F0-9]{2}[:][a-fA-F0-9]{2}[:][a-fA-F0-9]{2}',line)
            
            dnlist.append(dn)
            maclist.append(mac)
            dn = None

for dn, mac in zip(dnlist, maclist):
    print('{} {}'.format(dn, mac))

Finally if you want to record all the mac you can just add the '-' to the dn list:

import re

dnlist = []
maclist = []
 
with open('pppoe.txt','r') as f:
    for line in f:
        if line.strip() == '-':
            dnlist.append(['-'*10])
    
        if '@ttml' in line:
            dn = re.findall(r'\d{10}',line)
            dnlist.append(dn)

        if 'svc:1' in line:
            mac = re.findall(r'mac:[a-fA-F0-9]{2}[:][a-fA-AF0-9]{2}[:][a-fA-F0-9]{2}[:][a-fA-F0-9]{2}[:][a-fA-F0-9]{2}[:][a-fA-F0-9]{2}',line)
            maclist.append(mac)

for dn, mac in zip(dnlist, maclist):
    print('{} {}'.format(dn, mac))