I copyed the following from Knowbuddy's Gnutella FAQ
http://www.rixsoft.com/Knowbuddy/gnutellafaq.html#ttl

Just like TCP/IP packets (Your searches), gnutella packets have a TTL (Time To Live). The TTL starts off at some low number, like 5. Each time a packet is routed through a servent, the servent lowers the TTL by 1. Once the TTL hits 0 the packet is no longer forwarded. This helps to keep packets from circling the network forever. Also, each servent has the option to arbitrarily lower the TTL of a packet if it thinks it is unreasonable. So, even if I send all my packets with a TTL of 200, the odds are that most of the servents along the way are going to just immediately knock this down to a more reasonable number. The number of servents the packet has already been routed through is also noted, and acts as a sort of reverse-TTL