linux - How do I route a packet to use localhost as a gateway? -

i'm trying test gateway wrote(see what's easiest way test gateway? context). due issue i'd rather not into, gateway , "sender" have on same machine. have receiver(let's 9.9.9.9) gateway able reach.

so i'll run application ./sendstuff 9.9.9.9 send packets ip address.

the problem is: how packets destined 9.9.9.9 go gateway on localhost? i've tried:

sudo route add -host 9.9.9.9 gw 127.0.0.1 lo

sudo route add -host 9.9.9.9 gw <machine's external ip address> eth0

but neither of pass packets through gateway. i've verified correct ips present in sudo route. can do?

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per request, here route table, after running second command(ip addresses changed match question. x.y.z.t ip of machine i'm running on):

destination     gateway         genmask         flags metric ref    use iface 9.9.9.9         x.y.z.t         255.255.255.255 ugh   0      0        0 eth0 x.y.z.0         0.0.0.0         255.255.254.0   u     0      0        0 eth0 0.0.0.0         <gateway addr>  0.0.0.0         ug    100    0        0 eth0 

127.0.0.1 picking packets, forwarding them on merry way if ipv4 packet forwarding enabled. if it's not enabled, drop them.

if trying forward packets destined 9.9.9.9 127.0.0.1, iptables.

edit: try this:

iptables -t nat -a output -d 9.9.9.9 -j dnat --to-destination 127.0.0.1 

that should redirect traffic 9.9.9.9 localhost instead.