feat: WinDHCPD — Windows-native DHCP server
Python 3 + Scapy DHCP server with: - Full DORA handshake (DISCOVER/OFFER/REQUEST/ACK) - Multi-scope support with DHCP relay - Static MAC-to-IP bindings - Lease persistence (JSON) with auto-prune - NACK for invalid requests - Flask web management panel (dark theme, live refresh) - Admin-privileged scapy sniff on UDP 67
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"""Main DHCP server loop: sniff packets and dispatch to handlers."""
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from __future__ import annotations
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import logging
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import signal
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import socket
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import sys
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import threading
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import time
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from typing import Optional
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from scapy.all import sniff, send
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from .config import Config, Scope, StaticBinding
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from .lease import Lease, LeaseDB
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from .parser import (
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DHCPDISCOVER, DHCPREQUEST, DHCPRELEASE,
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DHCPMessage, parse,
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build_offer, build_ack, build_nak,
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)
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log = logging.getLogger("dhcpd.server")
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# ── counters ──────────────────────────────────────────────────────────────
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_msgs = {"DISCOVER": 0, "REQUEST": 0, "RELEASE": 0, "NAK": 0, "total": 0}
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class DHCPd:
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"""
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Non-blocking DHCP server.
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Runs scapy sniff in a background thread; packet handler runs in the same
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thread so lease DB access is effectively single-threaded.
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"""
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def __init__(
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self,
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config: Config,
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lease_db: LeaseDB,
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iface: Optional[str] = None,
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):
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self.config = config
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self.db = lease_db
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self.server_ip = config.server.get("ip", "")
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if not self.server_ip:
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# derive from first scope
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for sc in config.scopes:
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if sc.enable:
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# pick router as server IP if set, else first usable
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self.server_ip = sc.router or str(sc.start_ip - 1 if sc.start_ip > 1 else sc.start_ip)
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break
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self.iface = iface
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self._stop_event = threading.Event()
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self._thread: Optional[threading.Thread] = None
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# Bindings index: ip -> binding, mac -> binding
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self._binding_by_ip: dict = {}
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self._binding_by_mac: dict = {}
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for b in config.bindings:
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self._binding_by_ip[b.ip] = b
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self._binding_by_mac[b.mac] = b
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# ── public ───────────────────────────────────────────────────────────
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def start(self) -> None:
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self._thread = threading.Thread(target=self._run, daemon=True, name="dhcpd-sniff")
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self._thread.start()
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log.info("DHCP server started (server_ip=%s, interface=%s)",
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self.server_ip, self.iface or "<default>")
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def stop(self) -> None:
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log.info("Stopping DHCP server...")
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self._stop_event.set()
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if self._thread:
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self._thread.join(timeout=5)
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self.db.save()
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log.info("DHCP server stopped.")
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@property
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def stats(self) -> dict:
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return dict(_msgs)
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# ── internal ─────────────────────────────────────────────────────────
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def _run(self) -> None:
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bpf = "udp port 67 or udp port 68"
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log.info("Starting packet sniff on %s (BPF: %s)",
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self.iface or "<default>", bpf)
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try:
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sniff(
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iface=self.iface,
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filter=bpf,
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prn=self._handle_packet,
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stopper=lambda: self._stop_event.is_set(),
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store=False,
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)
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except Exception as e:
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log.error("Sniffer died: %s", e)
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log.info("Sniffer thread exited.")
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def _handle_packet(self, pkt) -> None:
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_msgs["total"] += 1
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msg = parse(pkt)
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if msg is None:
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return
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log.debug("Recv %s from %s xid=0x%x", msg.msg_name, msg.client_mac, msg.xid)
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try:
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if msg.msg_type == DHCPDISCOVER:
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_msgs["DISCOVER"] += 1
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self._handle_discover(msg)
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elif msg.msg_type == DHCPREQUEST:
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_msgs["REQUEST"] += 1
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self._handle_request(msg)
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elif msg.msg_type == DHCPRELEASE:
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_msgs["RELEASE"] += 1
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self._handle_release(msg)
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except Exception as e:
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log.exception("Error handling %s", msg.msg_name)
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# ── message handlers ─────────────────────────────────────────────────
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def _handle_discover(self, msg: DHCPMessage) -> None:
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"""
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DHCPDISCOVER -> DHCPOFFER
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Pick an address based on:
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1. Static binding for this MAC
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2. Requested IP in options (if present and valid)
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3. Auto-allocate from pool
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"""
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sc, offer_ip = self._pick_address(msg)
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if offer_ip is None:
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log.warning("DISCOVER: no address available for %s", msg.client_mac)
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return
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pkt = build_offer(
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req=msg,
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offer_ip=offer_ip,
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lease_seconds=sc.lease_seconds,
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server_ip=self.server_ip,
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router=sc.router,
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dns=sc.dns_servers,
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subnet_mask=sc.subnet_mask,
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domain=sc.domain,
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)
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send(pkt, iface=self.iface)
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log.info("OFFER %s -> %s (lease=%ds)", offer_ip, msg.client_mac, sc.lease_seconds)
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def _handle_request(self, msg: DHCPMessage) -> None:
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"""
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DHCPREQUEST -> DHCPACK or NAK
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Client may specify the requested IP in two ways:
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- ciaddr field (non-zero) = client already has an address
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- "requested_addr" DHCP option = newly requested
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- yiaddr from the OFFER (server must check)
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"""
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# Determine which IP the client wants
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requested_ip = msg.ciaddr if msg.ciaddr != "0.0.0.0" else None
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if not requested_ip:
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for o in (msg.options.get("param_req"),):
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pass # param_req is what client wants, not the address
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# Check if there's a "requested_addr" option
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# (parser currently doesn't expose it; derive from OFFER state)
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# Fallback: use the lease we offered
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lease = self.db.find_by_mac(msg.client_mac)
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if lease:
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requested_ip = lease.ip
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if requested_ip is None:
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log.warning("REQUEST from %s has no requested IP", msg.client_mac)
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return
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sc = self.config.scope_for_ip(requested_ip)
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if sc is None:
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log.warning("REQUEST for %s: no matching scope", requested_ip)
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self._send_nak(msg)
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_msgs["NAK"] += 1
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return
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# Check if a static binding maps this IP
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static = self._binding_by_ip.get(requested_ip)
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if static and static.mac != msg.client_mac.replace(":", ""):
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log.warning("REQUEST for %s but IP is statically bound to another MAC",
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requested_ip)
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self._send_nak(msg)
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_msgs["NAK"] += 1
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return
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# Mark lease as acknowledged
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now = time.time()
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lease = self.db.find_by_mac(msg.client_mac)
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if lease and lease.ip == requested_ip:
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lease.acknowledged_at = now
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lease.expires_at = now + sc.lease_seconds
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lease.scope = sc.name
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lease.hostname = msg.hostname or lease.hostname
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self.db.save()
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else:
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# New allocation that wasn't pre-allocated
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lease = Lease(
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mac=msg.client_mac,
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ip=requested_ip,
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hostname=msg.hostname,
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offered_at=now,
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acknowledged_at=now,
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expires_at=now + sc.lease_seconds,
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static=static is not None,
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scope=sc.name,
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)
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self.db.add(lease)
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pkt = build_ack(
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req=msg,
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offered_ip=requested_ip,
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lease_seconds=sc.lease_seconds,
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server_ip=self.server_ip,
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router=sc.router,
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dns=sc.dns_servers,
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subnet_mask=sc.subnet_mask,
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domain=sc.domain,
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)
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send(pkt, iface=self.iface)
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log.info("ACK %s -> %s (hostname=%s)", requested_ip, msg.client_mac, msg.hostname)
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def _handle_release(self, msg: DHCPMessage) -> None:
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"""Handle DHCPRELEASE: remove lease for this MAC."""
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lease = self.db.find_by_mac(msg.client_mac)
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if lease:
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ip = lease.ip
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self.db.release(msg.client_mac)
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log.info("RELEASE acknowledged: %s freed", ip)
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else:
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log.info("RELEASE for unknown MAC %s", msg.client_mac)
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# ── helpers ──────────────────────────────────────────────────────────
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def _pick_address(self, msg: DHCPMessage) -> tuple:
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"""
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Return (Scope, IP) to offer, or (Scope, None).
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"""
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# 1. Static binding
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binding = self.config.binding_for_mac(msg.client_mac)
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if binding:
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sc = self.config.scope_for_ip(binding.ip)
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if not sc:
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log.warning("Static binding for %s points to IP %s not in any scope",
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msg.client_mac, binding.ip)
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sc = self._select_scope(msg) # fallback
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if sc:
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# Mark as static in lease if not already
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lease = self.db.find_by_mac(msg.client_mac)
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if lease and not lease.static:
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lease.static = True
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lease.expires_at = time.time() + sc.lease_seconds
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self.db.save()
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return sc, binding.ip
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# 2. Auto-allocate: pick scope based on server/relay context
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sc = self._select_scope(msg)
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if sc is None:
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# fallback: first enabled scope
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for s in self.config.scopes:
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if s.enable:
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sc = s
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break
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if sc is None:
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return sc, None
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# Auto-allocate next free
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lease = self.db.find_by_mac(msg.client_mac)
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if lease and not lease.is_expired:
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return sc, lease.ip
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offer = self.db.allocate_next(
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start=str(sc.start_ip),
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end=str(sc.end_ip),
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mac=msg.client_mac,
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lease_seconds=sc.lease_seconds,
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xid=msg.xid,
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hostname=msg.hostname,
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scope=sc.name,
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)
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return sc, offer.ip if offer else None
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def _select_scope(self, msg: DHCPMessage) -> Optional[Scope]:
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"""Pick a scope based on giaddr (relay) or first enabled scope."""
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if msg.giaddr and msg.giaddr != "0.0.0.0":
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sc = self.config.scope_for_ip(msg.giaddr)
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if sc and sc.enable:
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return sc
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# Return first enabled scope
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for s in self.config.scopes:
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if s.enable:
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return s
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return None
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def _send_nak(self, msg: DHCPMessage) -> None:
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pkt = build_nak(msg, self.server_ip)
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send(pkt, iface=self.iface)
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