Hi all,

1. I run uml in linux1, 
./umlinux ubda=my_rootfs mem=128M eth0=tuntap,,,

2. after it boot up, i set the uml ip to be
    route add default gw

3. in the linux1, i add
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

4. linux 1 and linux 2 can ping each other
5. uml and linux1 can ping each other
6. uml can ping linux 2
7. but linux 2 cannot ping uml

pls advice what to do, thanks !