Kevin Veen-Birkenbach
c15127b6ab
See: https://chatgpt.com/share/68efc179-1a10-800f-9656-1e8731b40546 (German discussion)
327 lines
13 KiB
Python
Executable File
327 lines
13 KiB
Python
Executable File
#!/usr/bin/env python3
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"""
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wg_mtu_auto.py — Auto-detect egress IF, optionally probe Path MTU to one or more targets,
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compute the correct WireGuard MTU, and apply it.
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Examples:
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sudo ./main.py
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sudo ./main.py --force-egress-mtu 1452
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sudo ./main.py --pmtu-target 46.4.224.77 --pmtu-target 2a01:4f8:2201:4695::2
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sudo ./main.py --pmtu-target 46.4.224.77,2a01:4f8:2201:4695::2 --pmtu-policy min
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sudo ./main.py --prefer-wg-egress --auto-pmtu-from-wg
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./main.py --dry-run
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"""
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import argparse
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import ipaddress
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import os
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import pathlib
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import re
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import statistics
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import subprocess
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import sys
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# ----------------- helpers -----------------
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def run(cmd): # -> str
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return subprocess.run(
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cmd, check=False, stdout=subprocess.PIPE, stderr=subprocess.DEVNULL, text=True
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).stdout.strip()
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def rc(cmd): # -> int
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return subprocess.run(cmd, stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL).returncode
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def exists_iface(iface): # -> bool
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return pathlib.Path(f"/sys/class/net/{iface}").exists()
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def read_mtu(iface): # -> int
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with open(f"/sys/class/net/{iface}/mtu", "r") as f:
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return int(f.read().strip())
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def set_mtu(iface, mtu, dry):
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if dry:
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print(f"[wg-mtu] DRY-RUN: ip link set mtu {mtu} dev {iface}")
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else:
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subprocess.run(["ip", "link", "set", "mtu", str(mtu), "dev", iface], check=True)
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def require_root(dry):
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if not dry and os.geteuid() != 0:
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print("[wg-mtu][ERROR] Please run as root (sudo) or use --dry-run.", file=sys.stderr)
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sys.exit(1)
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def is_ipv6(addr): # -> bool
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try:
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return isinstance(ipaddress.ip_address(addr), ipaddress.IPv6Address)
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except ValueError:
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# best-effort for hostnames (contains ':')
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return ":" in addr
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# ----------------- route & iface selection -----------------
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def default_route_lines():
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lines = []
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for cmd in (["ip", "-4", "route", "show", "default"], ["ip", "-6", "route", "show", "default"]):
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out = run(cmd)
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if out:
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lines.extend(out.splitlines())
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return lines
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def get_default_ifaces(ignore_vpn=True): # -> list[str]
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devs = []
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for line in default_route_lines():
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m = re.search(r"\bdev\s+(\S+)", line)
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if m:
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devs.append(m.group(1))
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# fallback via route get
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if not devs:
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for cmd in (["ip", "route", "get", "1.1.1.1"], ["ip", "-6", "route", "get", "2606:4700:4700::1111"]):
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out = run(cmd)
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m = re.search(r"\bdev\s+(\S+)", out)
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if m:
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devs.append(m.group(1))
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uniq = []
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for d in devs:
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if not d or d == "lo" or not exists_iface(d):
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continue
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if ignore_vpn and re.match(r"^(wg|tun)\d*$", d):
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continue
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if d not in uniq:
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uniq.append(d)
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return uniq
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def wg_default_is_active(wg_if: str) -> bool:
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# check if any default route is via wg_if
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return any(re.search(rf"\bdev\s+{re.escape(wg_if)}\b", line) for line in default_route_lines())
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# ----------------- PMTU probing -----------------
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def ping_ok(payload, target, timeout_s): # -> bool
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base = ["ping", "-M", "do", "-c", "1", "-s", str(payload), "-W", str(max(1, int(round(timeout_s))))]
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if is_ipv6(target):
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base.insert(1, "-6")
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return rc(base + [target]) == 0
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def probe_pmtu(target, lo_payload=1200, hi_payload=1472, timeout=1.0): # -> int|None
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"""Binary-search the largest payload that passes with DF. Return Path MTU (payload + hdr) or None.
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Header: +28 (IPv4), +48 (IPv6)."""
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hdr = 48 if is_ipv6(target) else 28
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# ensure lower bound works; if not, try smaller floors
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if not ping_ok(lo_payload, target, timeout):
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for p in (1180, 1160, 1140):
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if ping_ok(p, target, timeout):
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lo_payload = p
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break
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else:
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return None
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lo, hi, best = lo_payload, hi_payload, None
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while lo <= hi:
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mid = (lo + hi) // 2
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if ping_ok(mid, target, timeout):
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best = mid
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lo = mid + 1
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else:
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hi = mid - 1
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return (best + hdr) if best is not None else None
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def choose_effective(pmtus, policy="min"): # -> int
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if not pmtus:
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raise ValueError("no PMTUs to choose from")
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if policy == "min":
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return min(pmtus)
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if policy == "max":
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return max(pmtus)
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if policy == "median":
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return int(statistics.median(sorted(pmtus)))
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raise ValueError(f"unknown policy {policy}")
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# ----------------- WireGuard helpers (opt-in) -----------------
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def wg_is_active(wg_if: str) -> bool:
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if not exists_iface(wg_if):
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return False
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return rc(["wg", "show", wg_if]) == 0
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def wg_peer_endpoints(wg_if: str) -> list[str]:
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"""Return list of peer endpoints (hostnames/IPs) – port stripped."""
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targets = []
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# 1) Try: wg show <if> endpoints
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out = run(["wg", "show", wg_if, "endpoints"])
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for line in out.splitlines():
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# format: <peer_public_key>\t<endpoint or (none)>
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parts = line.strip().split()
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if len(parts) >= 2 and parts[-1] != "(none)":
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ep = parts[-1] # host:port
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host = ep.rsplit(":", 1)[0]
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# IPv6 endpoint may be like [2001:db8::1]:51820
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host = host.strip("[]")
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targets.append(host)
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# 2) Fallback: wg showconf (root may be required)
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if not targets:
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conf = run(["wg", "showconf", wg_if])
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if conf:
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for m in re.finditer(r"^Endpoint\s*=\s*(.+)$", conf, flags=re.MULTILINE):
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ep = m.group(1).strip()
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host = ep.rsplit(":", 1)[0].strip("[]")
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targets.append(host)
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# dedupe & sanity
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cleaned = []
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for t in targets:
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if t and t not in cleaned:
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cleaned.append(t)
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return cleaned
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# ----------------- main -----------------
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def main():
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ap = argparse.ArgumentParser(description="Compute/apply WireGuard MTU based on egress MTU and optional multi-target PMTU probing.")
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ap.add_argument("--egress-if", help="Explicit egress interface (auto-detected if omitted).")
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ap.add_argument("--prefer-wg-egress", action="store_true",
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help="Allow/consider wg* as egress and prefer it if default route uses wg (default: disabled).")
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ap.add_argument("--auto-pmtu-from-wg", action="store_true",
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help="Automatically add WireGuard peer endpoints as PMTU targets (default: disabled).")
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ap.add_argument("--wg-if", default=os.environ.get("WG_IF", "wg0"), help="WireGuard interface name (default: wg0).")
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ap.add_argument("--wg-overhead", type=int, default=int(os.environ.get("WG_OVERHEAD", "80")), help="Bytes of WG overhead to subtract (default: 80).")
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ap.add_argument("--wg-min", type=int, default=int(os.environ.get("WG_MIN", "1280")), help="Minimum allowed WG MTU (default: 1280).")
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# PMTU (multi-target)
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ap.add_argument("--pmtu-target", action="append", help="Target hostname/IP to probe PMTU. Can be given multiple times OR comma-separated.")
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ap.add_argument("--pmtu-timeout", type=float, default=1.0, help="Timeout (seconds) per ping probe (default: 1.0).")
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ap.add_argument("--pmtu-min-payload", type=int, default=1200, help="Lower bound payload for PMTU search (default: 1200).")
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ap.add_argument("--pmtu-max-payload", type=int, default=1472, help="Upper bound payload for PMTU search (default: 1472 ~ 1500-28).")
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ap.add_argument("--pmtu-policy", choices=["min", "median", "max"], default="min",
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help="How to choose effective PMTU across multiple targets (default: min).")
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ap.add_argument("--apply-egress-mtu", action="store_true",
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help="Apply the effective Path MTU to the detected egress interface (e.g. eth0).")
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ap.add_argument("--dry-run", action="store_true", help="Show actions without applying changes.")
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# NEW: force a specific WireGuard MTU (overrides computed value)
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ap.add_argument("--set-wg-mtu", type=int, help="Force a specific MTU to apply on the WireGuard interface (overrides computed value).")
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# (legacy / optional) force egress MTU
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ap.add_argument("--force-egress-mtu", type=int, help="Force this MTU on the egress interface before computing wg MTU.")
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args = ap.parse_args()
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require_root(args.dry_run)
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# Egress detection (wg ignored by default)
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if args.egress_if:
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egress = args.egress_if
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else:
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ignore_vpn = not args.prefer_wg_egress
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cands = get_default_ifaces(ignore_vpn=ignore_vpn)
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# If we allow wg and default route is via wg-if, prefer it first
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if args.prefer_wg_egress and wg_is_active(args.wg_if) and wg_default_is_active(args.wg_if):
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if args.wg_if in cands:
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cands.remove(args.wg_if)
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cands.insert(0, args.wg_if)
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egress = cands[0] if cands else None
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if not egress:
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print("[wg-mtu][ERROR] Could not detect egress interface (use --egress-if).", file=sys.stderr)
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sys.exit(2)
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if not exists_iface(egress):
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print(f"[wg-mtu][ERROR] Interface {egress} does not exist.", file=sys.stderr)
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sys.exit(3)
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print(f"[wg-mtu] Detected egress interface: {egress}")
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# Egress MTU
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if args.prefer_wg_egress and egress == args.wg_if:
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print(f"[wg-mtu] Using WireGuard interface {args.wg_if} as egress basis.")
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if args.wg_if == egress and not wg_is_active(args.wg_if):
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print(f"[wg-mtu][WARN] {args.wg_if} selected as egress but WireGuard is not active.", file=sys.stderr)
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if args.force_egress_mtu:
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print(f"[wg-mtu] Forcing egress MTU {args.force_egress_mtu} on {egress}")
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set_mtu(egress, args.force_egress_mtu, args.dry_run)
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base_mtu = args.force_egress_mtu
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else:
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base_mtu = read_mtu(egress)
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print(f"[wg-mtu] Egress base MTU: {base_mtu}")
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# Build PMTU target list
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pmtu_targets = []
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if args.pmtu_target:
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for item in args.pmtu_target:
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pmtu_targets.extend([x.strip() for x in item.split(",") if x.strip()])
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if args.auto_pmtu_from_wg:
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if wg_is_active(args.wg_if):
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wg_targets = wg_peer_endpoints(args.wg_if)
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if wg_targets:
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print(f"[wg-mtu] Auto-added WG peer endpoints as PMTU targets: {', '.join(wg_targets)}")
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pmtu_targets.extend(wg_targets)
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else:
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print("[wg-mtu] INFO: No WG peer endpoints discovered (wg show/showconf).")
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else:
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print(f"[wg-mtu] INFO: {args.wg_if} is not active; skipping auto PMTU targets from WG.")
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# Deduplicate PMTU targets
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if pmtu_targets:
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pmtu_targets = list(dict.fromkeys(pmtu_targets))
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# PMTU probing
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effective_mtu = base_mtu
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if pmtu_targets:
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good = []
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print(f"[wg-mtu] Probing Path MTU for: {', '.join(pmtu_targets)} (policy={args.pmtu_policy})")
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for t in pmtu_targets:
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p = probe_pmtu(t, args.pmtu_min_payload, args.pmtu_max_payload, args.pmtu_timeout)
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print(f"[wg-mtu] - {t}: {p if p else 'probe failed'}")
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if p:
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good.append(p)
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if good:
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chosen = choose_effective(good, args.pmtu_policy)
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print(f"[wg-mtu] Selected Path MTU (policy={args.pmtu_policy}): {chosen}")
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effective_mtu = min(base_mtu, chosen)
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else:
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print("[wg-mtu] WARNING: All PMTU probes failed. Falling back to egress MTU.")
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# Optionally apply the effective MTU to the egress interface
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if args.apply_egress_mtu:
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if egress == args.wg_if:
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print(f"[wg-mtu] INFO: Skipping egress MTU apply because egress == {args.wg_if}.")
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else:
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print(f"[wg-mtu] Applying effective MTU {effective_mtu} to egress {egress}")
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set_mtu(egress, effective_mtu, args.dry_run)
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# Compute WG MTU
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wg_mtu = max(args.wg_min, effective_mtu - args.wg_overhead)
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print(f"[wg-mtu] Computed {args.wg_if} MTU: {wg_mtu} (overhead={args.wg_overhead}, min={args.wg_min})")
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# --- NEW: override with --set-wg-mtu if provided
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if args.set_wg_mtu is not None:
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if args.set_wg_mtu < args.wg_min:
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print(f"[wg-mtu][WARN] --set-wg-mtu {args.set_wg_mtu} is below wg-min {args.wg_min}; clamping to {args.wg_min}.")
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args.set_wg_mtu = args.wg_min
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wg_mtu = args.set_wg_mtu
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print(f"[wg-mtu] Forcing WireGuard MTU (override): {wg_mtu}")
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# Apply
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if exists_iface(args.wg_if):
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set_mtu(args.wg_if, wg_mtu, args.dry_run)
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print(f"[wg-mtu] Applied: {args.wg_if} MTU {wg_mtu}")
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else:
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print(f"[wg-mtu] NOTE: {args.wg_if} not present yet. Start WireGuard first, then re-run this script.")
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print(f"[wg-mtu] Done. Summary: egress={egress} mtu={base_mtu}, effective_mtu={effective_mtu}, {args.wg_if}_mtu={wg_mtu}")
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if __name__ == "__main__":
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main()
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