def callback(frame):
'''
The action after receiving datagram from link layer.
First unpack datagram
Case1: if the outside datagram is received by destination end router,
it will first do NAT and update datgram, then push upward
Case2; if the internal datagram is received by destination,
no need for NAT, directly push upward
Case3: if this datagram is received in core routers,
find the next forwarding hop ip and convert into mac,
then send it by linklayer
:param frame: received datagram from linklayer
:return: None
'''
network, transport, action = unpack(frame)
if action == ACTION_PUSH:
if network.dst_ip == util.get_local_ipv4_address():
IP.push(frame)
elif network.dst_ip in forwarding_table:
forwarding_ip = forwarding_table[network.dst_ip]
if forwarding_ip != WAN_ip:
dst_ip = forwarding_ip
else:
dst_ip = network.dst_ip
if dst_ip != forwarding_ip:
print('forwaring to', forwarding_table[network.dst_ip])
dst_mac = util.ip2mac(dst_ip)
linklayer.sendto(dst_mac, frame)
elif (network.dst_ip, transport.dst_port) in NAT_in :
network.dst_ip, transport.dst_port = NAT_in[(network.dst_ip, transport.dst_port)]
frame = pack(network, transport)
IP.push(frame)
else:
ICMP.host_unreachable(WAN_ip, network.src_ip)
def send(datagram, dst_ip, nat = False): # todo read from file
'''
This send method is for both end router and router in core
:param datagram: sending content
:param dst_ip: destination ip
:param nat: a tune to remark current send is for end router or core router
:return: None
'''
# [for present]
import json
with open('show.json', 'r') as f:
dict_ = json.loads(f.read())
nat = dict_['nat']
if nat == 'True':
nat = True
elif nat == 'False':
nat = False
else:
raise Exception("Wrong show.json")
# [end]
if nat:
# for end router, do NAT first
datagram = NAT(datagram,'out')
dst_ip = forwarding_table[dst_ip]
linklayer.sendto(util.ip2mac(dst_ip),datagram)
def senddatagram(self, ip_src, ip_dst, ttl, ip_proto, data):
datagram = Datagram.pack_datagram(ip_src, ip_dst, ttl, ip_proto, data)
## Here, let's set dst_mac according to our program >>>>
dst_mac = util.ip2mac(loadConfig.loadDstIP())
self.sendto(dst_mac, datagram, None)
""" how to acquire dst_mac"""
from LinkLayer import LinkLayer, util
def callback(frame):
print(frame)
link = LinkLayer(callback)
link.sendto(util.ip2mac("10.20.16.17"), b'hheelekd', None)