Fragroute

fragroute intercepts, modifies, and rewrites egress traffic destined for a specified host, implementing most of the attacks described in the Secure Networks "Insertion, Evasion, and Denial of Service: Eluding Network Intrusion Detection" paper of January 1998.
It features a simple ruleset language to:
delay
duplicate
drop
fragment
overlap
print
reorder
segment
source-route
or otherwise monkey with
all outbound packets destined for a target host, with minimal support for randomized or probabilistic behavior.