Accordingly, Song and Perrig propose the following traceback scheme: instead of encoding the IP address interleaved with a hash, they suggest encoding the IP address into an 11 bit hash and maintain a 5 bit hop count, both stored in the 16-bit fragment ID field. This is based on the observation that a 5-bit hop count (32 max hops) is sufficient for almost all Internet routes. Further, they suggest that two different hashing functions be used so that the order of the routers in the markings can be determined. Next, if any given hop decides to mark it first checks the distance field for a 0, which implies that a previous router has already marked it. If this is the case, it generates an 11-bit hash of its own IP address and then XORs it with the previous hop. If it finds a non-zero hop count it inserts its IP hash, sets the hop count to zero and forwards the packet on. If a router decides not to mark the packet it merely increments the hop count in the overloaded fragment id field.