There is no need to do "table lookups of hop count" or to "decrement hop counts". The IP TTL value is just a field that can be read from the IP header, which is trivial since the Python would get the entire IP header from the raw socket. If you see a TTL=1 you send back the forged response as coming from $IP_1, if you see a TTL=2 you forge the response as coming from $IP_2, etc. The forged response can always contain the same default TTL.