Scapy srp1 timeout request

Question

I'm trying to build a tracert with python. I made a loop that runs ttl times to show all the source ip's that the message has passed.

I understand that there are some "stations" that doesn't return ttl exceeded, so I need to create a timeout request with the srp, I don't really know what does srp1(msg, timeout = 10) will return to me because I cant see the returned message

I got the TTL size to run in the loop, just need to know what do to if timeout passed.

for i in range(1,ttl+1):
    msg = Ether() / IP(dst = domain, ttl = i) / ICMP()
    ans = srp1(msg, verbose = 0, timeout = 10)
    print("%d: %s" % (i, ans[IP].src))

Answer 1

If a timeout occurs srp1 will return None.

if ans is not None:
    print("%d: %s" % (i, ans[IP].src))
else:
    print("%d: Timeout waiting for %s" % (i, fullmsg[IP].dst))

timeout=2 should be a good value.