Eu precisaria de mais informações, mas tentarei adivinhar (supondo que você possa trabalhar com uma distribuição Linux):
If ("multiple IP access" doesn't mean different IPs)
{
If (your application doesn't need interaction, but only an http request)
{
I would try several wget in parallel launched from a shell script
}
else // == your application needs interaction
{
Can you program a light client (let's say python, java...) to simulate one client and launch several simultaneously?
}
}
else // == you need different IPs
{
If (the IPs need to be public)
{
I would try to work on wget/light client accesing different proxy servers on the Internet.
}
else // == they can be private
{
I would first try to create about 500 subinterfaces (eth0:n). This means 2 /24, and some work on address space on your private site. Once you have the subinterfaces, I would try the wget/light client over different subinterfaces.
}
}