Allow to disable auto-loading of routes

doc/scapy/usage.rst

@@ -1794,6 +1794,39 @@ There are quite a few ways of speeding up scapy's dissection. You can use all of
     # Disable filtering: restore everything to normal
     conf.layers.unfilter()
 
+Very slow start because of big routes
+-------------------------------------
+
+Problem
+^^^^^^^
+
+Scapy takes ages to start because you have very big routing tables.
+
+Solution
+^^^^^^^^
+
+Disable the auto-loading of the routing tables:
+
+**CLI:** in ``~/.config/scapy/prestart.py`` add:
+
+.. code:: python
+
+    conf.route_autoload = False
+    conf.route6_autoload = False
+
+**Programmatically:**
+
+.. code:: python
+
+    # Before any other Scapy import
+    from scapy.config import conf
+    conf.route_autoload = False
+    conf.route6_autoload = False
+    # Import Scapy here
+    from scapy.all import *
+
+At anytime, you can trigger the routes loading using ``conf.route.resync()`` or ``conf.route6.resync()``, or add the routes yourself `as shown here <#routing>`_.
+
 
 OS Fingerprinting
 -----------------

scapy/config.py

@@ -970,6 +970,12 @@ class Conf(ConfClass):
     neighbor = None  # type: 'scapy.layers.l2.Neighbor'
     #: holds the name servers IP/hosts used for custom DNS resolution
     nameservers = None  # type: str
+    #: automatically load IPv4 routes on startup. Disable this if your
+    #: routing table is too big.
+    route_autoload = True
+    #: automatically load IPv6 routes on startup. Disable this if your
+    #: routing table is too big.
+    route6_autoload = True
     #: holds the Scapy IPv4 routing table and provides methods to
     #: manipulate it
     route = None  # type: 'scapy.route.Route'

scapy/route.py

@@ -32,7 +32,9 @@ class Route:
     def __init__(self):
         # type: () -> None
         self.routes = []  # type: List[Tuple[int, int, str, str, str, int]]
-        self.resync()
+        self.invalidate_cache()
+        if conf.route_autoload:
+            self.resync()
 
     def invalidate_cache(self):
         # type: () -> None

scapy/route6.py

@@ -40,8 +40,11 @@ class Route6:
 
     def __init__(self):
         # type: () -> None
-        self.resync()
+        self.routes = []  # type: List[Tuple[str, int, str, str, List[str], int]]  # noqa: E501
+        self.ipv6_ifaces = set()  # type: Set[Union[str, NetworkInterface]]
         self.invalidate_cache()
+        if conf.route6_autoload:
+            self.resync()
 
     def invalidate_cache(self):
         # type: () -> None
@@ -50,8 +53,8 @@ def invalidate_cache(self):
     def flush(self):
         # type: () -> None
         self.invalidate_cache()
-        self.ipv6_ifaces = set()  # type: Set[Union[str, NetworkInterface]]
-        self.routes = []  # type: List[Tuple[str, int, str, str, List[str], int]]  # noqa: E501
+        self.routes.clear()
+        self.ipv6_ifaces.clear()
 
     def resync(self):
         # type: () -> None