diff --git a/httpd.py b/httpd.py
index 60d7017..2207fff 100644
--- a/httpd.py
+++ b/httpd.py
@@ -31,6 +31,56 @@ except (ImportError, IOError, ValueError):
     _geodb = None
     _geolite = False
 
+# ASN lookup (optional) - try pyasn first, fall back to pure-Python reader
+_asndb = None
+_asn_dat_path = os.path.join("data", "ipasn.dat")
+try:
+    import pyasn
+    _asndb = pyasn.pyasn(_asn_dat_path)
+except (ImportError, IOError):
+    pass
+
+if _asndb is None and os.path.exists(_asn_dat_path):
+    import socket
+    import struct
+    import bisect
+
+    class _AsnLookup(object):
+        """Pure-Python ASN lookup using ipasn.dat (CIDR/ASN text format)."""
+
+        def __init__(self, path):
+            self._entries = []
+            with open(path) as f:
+                for line in f:
+                    line = line.strip()
+                    if not line or line.startswith(';'):
+                        continue
+                    parts = line.split('\t')
+                    if len(parts) != 2:
+                        continue
+                    cidr, asn = parts
+                    ip, prefix = cidr.split('/')
+                    start = struct.unpack('!I', socket.inet_aton(ip))[0]
+                    self._entries.append((start, int(prefix), int(asn)))
+            self._entries.sort()
+            _log('asn: loaded %d prefixes (pure-python)' % len(self._entries), 'info')
+
+        def lookup(self, ip):
+            ip_int = struct.unpack('!I', socket.inet_aton(ip))[0]
+            idx = bisect.bisect_right(self._entries, (ip_int, 33, 0)) - 1
+            if idx < 0:
+                return (None, None)
+            start, prefix_len, asn = self._entries[idx]
+            mask = (0xFFFFFFFF << (32 - prefix_len)) & 0xFFFFFFFF
+            if (ip_int & mask) == (start & mask):
+                return (asn, None)
+            return (None, None)
+
+    try:
+        _asndb = _AsnLookup(_asn_dat_path)
+    except Exception as e:
+        _log('asn: failed to load %s: %s' % (_asn_dat_path, e), 'warn')
+
 # Rate limiting configuration
 _rate_limits = defaultdict(list)
 _rate_lock = threading.Lock()
@@ -604,7 +654,7 @@ def submit_proxy_reports(db, worker_id, proxies):
             ''', (proxy_key, ip, port, proto, now_int, now_int, latency, now_int,
                   checktype, target))
 
-            # Geolocate if IP2Location available
+            # Geolocate and ASN lookup
             if _geolite and _geodb:
                 try:
                     rec = _geodb.get_all(ip)
@@ -614,6 +664,15 @@ def submit_proxy_reports(db, worker_id, proxies):
                             (rec.country_short, proxy_key))
                 except Exception:
                     pass
+            if _asndb:
+                try:
+                    asn_result = _asndb.lookup(ip)
+                    if asn_result and asn_result[0]:
+                        db.execute(
+                            'UPDATE proxylist SET asn=? WHERE proxy=?',
+                            (asn_result[0], proxy_key))
+                except Exception:
+                    pass
 
             # Track per-URL working count for working_ratio
             if source_url:
@@ -1306,6 +1365,9 @@ class ProxyAPIServer(threading.Thread):
         load_static_files(THEME)
         # Load worker registry from disk
         load_workers()
+        # Backfill ASN for existing proxies missing it
+        if _asndb:
+            self._backfill_asn()
         # Create verification tables if they don't exist
         try:
             db = mysqlite.mysqlite(self.database, str)
@@ -1314,6 +1376,31 @@ class ProxyAPIServer(threading.Thread):
         except Exception as e:
             _log('failed to create verification tables: %s' % e, 'warn')
 
+    def _backfill_asn(self):
+        """One-time backfill of ASN for proxies that have ip but no ASN."""
+        try:
+            db = mysqlite.mysqlite(self.database, str)
+            rows = db.execute(
+                'SELECT proxy, ip FROM proxylist WHERE asn IS NULL AND ip IS NOT NULL'
+            ).fetchall()
+            if not rows:
+                return
+            updated = 0
+            for proxy_key, ip in rows:
+                try:
+                    result = _asndb.lookup(ip)
+                    if result and result[0]:
+                        db.execute('UPDATE proxylist SET asn=? WHERE proxy=?',
+                                   (result[0], proxy_key))
+                        updated += 1
+                except Exception:
+                    pass
+            db.commit()
+            if updated:
+                _log('asn: backfilled %d/%d proxies' % (updated, len(rows)), 'info')
+        except Exception as e:
+            _log('asn backfill error: %s' % e, 'warn')
+
     def _wsgi_app(self, environ, start_response):
         """WSGI application wrapper for gevent."""
         path = environ.get('PATH_INFO', '/').split('?')[0]