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April 26, 2017 01:32
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A script to check the SOA serial numbers of all nameservers of a domain and notify via Zephyr
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#!/usr/bin/env python3 | |
from __future__ import print_function | |
import sys | |
import time | |
import dns.resolver, dns.exception | |
from random import randrange | |
import zwrite | |
DEFAULT_ARGS = {"classname": "test", | |
"instance": "dns", | |
"sender": "dns_bot", | |
"opcode": "auto"} | |
TEMPLATE = "{:15} SOA Serial: @b({})" | |
DEFAULT_INTERVAL = 300 | |
BACKOFF_START = 10 | |
def find_nameservers(domain): | |
nameservers = [] | |
try: | |
answer = dns.resolver.query(domain, "NS") | |
for ns in answer: | |
nameservers.append(ns.target) | |
return nameservers | |
except dns.resolver.NoNameservers: | |
print("Error: Cannot find name servers for {}.".format(domain)) | |
raise | |
def find_ips(domains): | |
ips = [] | |
for d in domains: | |
answer = dns.resolver.query(d) | |
for a in answer: | |
ips.append(a.address) | |
return ips | |
def spawn_resolvers(nameservers): | |
resolvers = [] | |
for ns in nameservers: | |
resolvers.append(dns.resolver.Resolver()) | |
resolvers[-1].nameservers = [ns] | |
return resolvers | |
def serials_gt(a, b): | |
# TODO: actually use the algorithm specified in RFC 1982 | |
return int(a) > int(b) | |
def serials_eq(a, b): | |
return int(a) == int(b) | |
def check_soa_serial(domain, resolvers, serials): | |
answers = [] | |
new_serials = {} | |
updated = False | |
for r in resolvers: | |
n = r.nameservers[0] | |
try: | |
soa = r.query(domain, "SOA") | |
s = soa[0].serial | |
if serials_gt(s, serials[n]): | |
answers.append(TEMPLATE.format(n, s) + " @b(@color(green)UPDATE)") | |
updated = True | |
elif serials_eq(s, serials[n]): | |
if updated: | |
answers.append(TEMPLATE.format(n, s) + " @b(@color(yellow)UNCHANGED)") | |
else: | |
answers.append(TEMPLATE.format(n, s) + " @b(@color(red)REGRESSION)") | |
updated = True | |
new_serials[n] = s | |
except dns.resolver.NoNameservers: | |
answers.append(TEMPLATE.format(n, "@color(red)UNKNOWN")) | |
serials.update(new_serials) | |
return "\n".join(answers) | |
def main(): | |
domain = sys.argv[1] | |
try: | |
resolver_ips = find_ips(find_nameservers(domain)) | |
except (dns.exception.Timeout, dns.resolver.NXDOMAIN, dns.resolver.YXDOMAIN, | |
dns.resolver.NoAnswer, dns.resolver.NoNameservers) as err: | |
if len(sys.argv) > 2: | |
resolver_ips = sys.argv[2:] | |
else: | |
zwrite.zwrite(str(err), zsig=domain, **DEFAULT_ARGS) | |
raise | |
resolvers = spawn_resolvers(resolver_ips) | |
serials = {} | |
for r in resolvers: | |
serials[r.nameservers[0]] = "0" | |
wait = DEFAULT_INTERVAL | |
timeout = 0 | |
while True: | |
try: | |
message = check_soa_serial(domain, resolvers, serials) | |
if message: | |
zwrite.zwrite(message, zsig=domain, **DEFAULT_ARGS) | |
wait = DEFAULT_INTERVAL | |
timeout = 0 | |
time.sleep(wait) | |
except dns.exception.Timeout as err: | |
zwrite.zwrite(str(err) + "\nRetry in {} seconds".format(wait), zsig=domain, **DEFAULT_ARGS) | |
wait = randrange(0, BACKOFF_START * 2**timeout) | |
timeout += 1 | |
time.sleep(wait) | |
if __name__ == "__main__": | |
main() |
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