dnsstuff

DNS and network diagnostics for mail relays and LANs: an SPF crawler that feeds a Linux ipset, a Microsoft 365 21Vianet IP-range updater, and an mDNS resolver that shows which host actually answered.

Modules

• spf_ipset_updater.py — recursively resolves the SPF records of the given domains (include:, a, mx, ip4, redirects), collects every IPv4 address and network and atomically swaps the result into a kernel ipset via netlink (pyroute2). Meant for SMTP allowlists on relay hosts.
• update_21vianet_ips.py — polls the Microsoft 365 endpoint API for the 21Vianet (China) Exchange Online ranges, caches the version and updates two ipsets: all Exchange IPv4 networks and the SMTP-only (port 25) subset.
• mdns_who.py — sends an mDNS query for a .local name itself and reports every responder: source IP, advertised A records, TTL and cache-flush bit. Flags proxied, cached or reflected replies (source IP ≠ advertised IP, more than one responder). --unicast adds a system-resolver lookup to surface a stale router DHCP lease.

Logging (loguru, with an intercept for stdlib logging from dnspython, pyroute2, urllib) and the startup banner are shared via somestuff.dnsstuff.

Installation

pip install somestuff-dnsstuff

somestuff is a PEP 420 namespace; the package is imported as somestuff.dnsstuff and shares the namespace with the other somestuff-* distributions.

Usage

Console scripts and module invocation are equivalent:

spf-ipset-updater example.com mail.example.net --ipset-name smtpallowlist
python3 -m somestuff.dnsstuff.spf_ipset_updater example.com --dry-run -v

update-21vianet-ips --ipset-name-all 21vianet_exchange --ipset-name-smtp 21vianet_smtp
python3 -m somestuff.dnsstuff.update_21vianet_ips --force --dry-run

mdns-who printer.local
python3 -m somestuff.dnsstuff.mdns_who printer --timeout 3 --unicast --iface 192.0.2.5

Common flags: --dry-run populates the ipset but skips the atomic swap, --no-comment disables the ipset comment extension, -v enables DEBUG logging. update-21vianet-ips --help lists the cache directory and API timeout options.

Cron example for the 21Vianet updater (daily at 03:00):

0 3 * * * update-21vianet-ips 2>&1 | logger -t 21vianet

Library

from somestuff.dnsstuff import configure_logging
from somestuff.dnsstuff.spf_ipset_updater import get_spf_records

configure_logging(verbose=True)

Privileges

• spf-ipset-updater and update-21vianet-ips modify kernel ipsets over netlink and need CAP_NET_ADMIN (in practice: root).
• mdns-who binds a UDP socket on port 5353 and joins the mDNS multicast group; on most systems this works unprivileged unless another mDNS daemon holds the port exclusively.

Notes

• Requires: dnspython, pyroute2, loguru, tabulate. Linux only (netlink ipsets).
• Licensed under the LGPL, see LICENSE.md in the repository root.