def wrong_checksum_a(testname):
hs = TESTS[testname].host_s
hr = TESTS[testname].host_r
r_mac = info.get("router_mac", hs)
target_ip = info.get("host_ip", hr)
i = IP(dst=target_ip)
chk = checksum(bytes(i))
chk = (chk + 1) % (2**16)
i.chksum = chk
return Ether(dst=r_mac) / i
def forward_p(testname, packets):
# The router may or may not (depending on its ARP cache) also send us an
# ARP request
hs = TESTS[testname].host_s
hr = TESTS[testname].host_r
res, packets = cull_dull_packets(hr, packets)
icmp_ur, packets = cull_icmp_unreachable(hr, packets)
if not len(packets):
error("No packet received")
return False
nr_pkts = 2 if testname == "forward_no_arp" else 1
if not res or len(packets) > nr_pkts:
error("Excess packets:")
dump_packets(packets)
return False
p = packets[0]
assert IP in p, "no IP packet from router"
i = p[IP]
result = True
if testname == "ttl":
crt = i.ttl == 63
if not crt:
error("Wrong TTL value")
error("Expected: ttl=63")
error("Got: ttl={}".format(i.ttl))
result = result and crt
if testname == "checksum":
router_chk = i.chksum
i.chksum = 0
correct_chk = checksum(bytes(i))
crt = router_chk == correct_chk
if not crt:
error("Wrong checksum value")
error("Expected: checksum=0x{:04x}".format(correct_chk))
error("Got: checksum=0x{:04x}".format(i.chksum))
result = result and crt
crt = i.dst == info.get("host_ip", hr)
if not crt:
error("Wrong IP destination value")
error("Expected: destination={}".format(info.get("host_ip", hr)))
error("Got: destination={}".format(i.dst))
result = result and crt
crt = i.src == info.get("host_ip", hs)
if not crt:
error("Wrong IP source value")
error("Expected: destination={}".format(info.get("host_ip", hs)))
error("Got: destination={}".format(i.src))
result = result and crt
return result