This is used to modify the IPv4 TTL header field.  The TTL field determines
how many hops (routers) a packet can traverse until it's time to live is
exceeded.
.TP
Setting or incrementing the TTL field can potentially be very dangerous,
so it should be avoided at any cost.  
.TP
.B Don't ever set or increment the value on packets that leave your local network!
.B mangle
table.
.TP
.BI "--ttl-set " "value"
Set the TTL value to `value'.
.TP
.BI "--ttl-dec " "value"
Decrement the TTL value `value' times.
.TP
.BI "--ttl-inc " "value"
Increment the TTL value `value' times.