VirtualBox 里配路由，出现问题

virtuaklBox
os CentOS release 4.5
eth0  ip :    192.168.10.130
#ip route
192.168.10.128/25 dev eth0 scope link
169.254.0.0/16 dev eth0
default via 192.168.10.129 dev eth0


host
os Ubuntu 7.04
echo 1 > /proc/sys/net/ipv4/ip_forward
tunctl -t tap0 -u  VBuser
ath0: <BROADCAST,MULTICAST,UP,10000> mtu 1500 qdisc noqueue
    link/ether 00:14:78:76:d4:26 brd ff:ff:ff:ff:ff:ff
    inet 192.168.10.10/24 brd 192.168.10.255 scope global ath0
    inet6 fe80::214:78ff:fe76:d426/64 scope link
       valid_lft forever preferred_lft forever
tap0: <BROADCAST,MULTICAST,UP,10000> mtu 1500 qdisc pfifo_fast qlen 500
    link/ether ce:d7:90:a6:15:ef brd ff:ff:ff:ff:ff:ff
    inet 192.168.10.129/25 brd 192.168.10.255 scope global tap0
    inet6 fe80::ccd7:90ff:fea6:15ef/64 scope link
       valid_lft forever preferred_lft forever
# ip route
192.168.10.128/25 dev tap0  proto kernel  scope link  src 192.168.10.129
192.168.10.0/24 dev ath0  proto kernel  scope link  src 192.168.10.10
169.254.0.0/16 dev ath0  scope link  metric 1000
default via 192.168.10.1 dev ath0


virtuaklBox      Host Interface      tap0


host
ping 192.168.10.1  ok
ping 192.168.10.130 ok

virtuaklBox
ping  192.168.10.129 ok
ping  192.168.10.1 lost                     why ?　　　　　　

192.168.10.128/25
为什么要这样设?　　　　　　

192.168.10.128/25 是 192.168.10.0/24的一个子网,外面的路由只要配192.168.10.0/24的就可以了