#!/usr/bin/python
# -*- encoding: utf-8 -*-
# ***************************************************************************************
# get_routing_table.py
# Retrieves a list of the router's interfaces and the routing table using SNMP queries.
# ***************************************************************************************
# v2.0 (c) Jarmo Pietiläinen 2013-2014
# Licensed under the zlib/libpng license.
# ***************************************************************************************
# Tested with Python 2.7.x under Debian 7 (Wheezy) and 8 (Jessie), XUbuntu 13.10 and
# Windows 7. Requires pysnmp and pyasn1 libraries to be installed.
# I do not know if this works with Python 3.
# ***************************************************************************************

import sys
from pysnmp.entity.rfc3413.oneliner import cmdgen

# subnet mask -> CIDR prefix length lookup table
subnet_masks = {
    "128.0.0.0" : 1, "255.128.0.0" : 9,  "255.255.128.0" : 17, "255.255.255.128" : 25,
    "192.0.0.0" : 2, "255.192.0.0" : 10, "255.255.192.0" : 18, "255.255.255.192" : 26,
    "224.0.0.0" : 3, "255.224.0.0" : 11, "255.255.224.0" : 19, "255.255.255.224" : 27,
    "240.0.0.0" : 4, "255.240.0.0" : 12, "255.255.240.0" : 20, "255.255.255.240" : 28,
    "248.0.0.0" : 5, "255.248.0.0" : 13, "255.255.248.0" : 21, "255.255.255.248" : 29,
    "252.0.0.0" : 6, "255.252.0.0" : 14, "255.255.252.0" : 22, "255.255.255.252" : 30,
    "254.0.0.0" : 7, "255.254.0.0" : 15, "255.255.254.0" : 23, "255.255.255.254" : 31,
    "255.0.0.0" : 8, "255.255.0.0" : 16, "255.255.255.0" : 24, "255.255.255.255" : 32
}

# subnet mask -> prefix length, returns 0 if invalid/zero
def mask_to_prefix(mask):
    return subnet_masks.get(mask, 0)


# returns True if the IP address is valid, False if not
def is_valid_ip(ip_str):
    try:
        b = [int(o) for o in ip_str.strip().split(".")]
    except:
        return False

    if (len(b) != 4) or (min(b) < 0) or (max(b) > 255):
        return False

    return True


# given a dotted OID string, this extracts an IPv4 address from
# the end of it (ie. the last four decimals)
def extract_ip_from_oid(oid):
    return ".".join(oid.split(".")[-4:])


# ---------------------------------------------------------------------------------------


if len(sys.argv) != 3:
    quit("Usage: get_routing_table.py <target IP> <community string>")

ip = sys.argv[1]

if not is_valid_ip(sys.argv[1]):
    quit("%s is not a valid IPv4 address" % (ip))

command_generator = cmdgen.CommandGenerator()
authentication = cmdgen.CommunityData(sys.argv[2])
target = cmdgen.UdpTransportTarget((ip, 161))

# send a GETBULK request for the OIDs we want
snmp_engine_error, error_status, error_index, variables = command_generator.bulkCmd(
    authentication, target, 0, 25,

    # destination network <-> subnet mask
    "1.3.6.1.2.1.4.21.1.11",

    # destination network <-> next-hop interface address
    "1.3.6.1.2.1.4.21.1.7",

    # interface index <-> ip address
    "1.3.6.1.2.1.4.20.1.2",

    # interface ip <-> subnet mask
    "1.3.6.1.2.1.4.20.1.3",

    # interface index <-> name (MIB extensions)
    "1.3.6.1.2.1.31.1.1.1.1"
)

if snmp_engine_error:
    quit(snmp_engine_error)

if error_status:
    quit("%s at %s" % (error_status.prettyPrint(), error_index and variables[int(error_index) - 1][0] or '?'))

# extract the data we need from the response
if_index_to_name = {}
if_index_to_address = {}
if_ip_to_subnet_mask = {}
destination_mask = {}
destination_next_hop = {}

longest = 0

for r in variables:
    for name, val in r:
        oid = name.prettyPrint()
        value = val.prettyPrint()

        # == INTERFACES ==

        # 1-based index <-> interface name
        if oid[0:23] == "1.3.6.1.2.1.31.1.1.1.1.":
            if_index_to_name[int(oid[oid.rindex(".") + 1:])] = value
            longest = max(longest, len(value))

        # 1-based index <-> interface ip address
        if oid[0:20] == "1.3.6.1.2.1.4.20.1.2":
            if_index_to_address[int(value)] = extract_ip_from_oid(oid)

        # ip address <-> subnet mask
        if oid[0:20] == "1.3.6.1.2.1.4.20.1.3":
            if_ip_to_subnet_mask[extract_ip_from_oid(oid)] = value

        # == ROUTING TABLE ==

        # destination network address <-> subnet mask
        if oid[0:21] == "1.3.6.1.2.1.4.21.1.11":
            destination_mask[extract_ip_from_oid(oid)] = value

        # destination network address <-> next-hop address
        if oid[0:20] == "1.3.6.1.2.1.4.21.1.7":
            destination_next_hop[extract_ip_from_oid(oid)] = value


# print a list of interfaces
print("Interfaces")

if len(if_index_to_name) == 0:
    print("Could not get the interface table, dumping raw data instead")
    print(if_index_to_address)
    print(if_ip_to_subnet_mask)

for i in if_index_to_name:
    padded_name = if_index_to_name[i].ljust(longest, ".") + ": "

    if i not in if_index_to_address:
        print("  " + padded_name + " (no address)")
        continue

    ip = if_index_to_address[i]

    if ip in if_ip_to_subnet_mask:
        mask = "/" + str(mask_to_prefix(if_ip_to_subnet_mask[ip]))
    else: mask = " (unknown subnet mask)"

    print("  " + padded_name + ip + mask)

#print the routing table
print("\nRouting table")

for d in destination_mask:
    if d not in destination_next_hop:
        next_hop = "(unknown)"
    else:
        addr = destination_next_hop[d]

        if addr == "0.0.0.0":
            next_hop = " (directly connected)"
        else: next_hop = " via " + addr

    print("  " + d + "/" + str(mask_to_prefix(destination_mask[d])) + next_hop)