nmap from net A to net B, don't work, but ping yes

["rmarfisi () inwind it" <rmarfisi () inwind it>]

I have 4 pc

pc1 10.10.1.101
pc2 eth0: 10.10.1.101; eth1:10.10.10.101
pc3

10.10.1.102
pc4 10.10.1.103

pc2 have this routing table:
10.10.1.0      

0.0.0.0         255.255.255.0   U     0      0        0 eth0
10.10.10.0     

0.0.0.0         255.255.255.0   U     0      0        0 eth1
0.0.0.0        

10.10.10.1      0.0.0.0         UG    0      0        0 eth1

in pc1:


10.10.1.0       10.10.10.101    255.255.255.0   UG    0      0        0 eth1


10.0.0.0        0.0.0.0         255.0.0.0       U     0      0        0 eth1


0.0.0.0         10.10.10.1      0.0.0.0         UG    0      0        0 eth1



in pc3, pc4:
10.10.1.0       0.0.0.0         255.255.255.0   U     0     

0        0 eth0
0.0.0.0         10.10.1.101     0.0.0.0         UG    0     

0        0 eth0

it'is a router between 10.10.1.0/24 and 10.10.10.0/24
i do in

pc2: sysctl -w net.ipv4.ip_forward=1

when i ping from pc1 to pc3 it works fine



but if i do from pc1 to 10.10.1.0/24
nmap -sS -A 10.10.1.0/24

it find only

pc2 (router) because it have eth1 in the same network of pc1

in the same time

if i do from pc2:
tcpdump -n -i eth0
it don't capture nothing

but
tcpdump -n -

i eth1
capture the traffic

why this behavior?

thanks a lot and scuse me for

my bad english