config ipfilter error

[hongjing_zhang]

when I config ipfilter:
a2#[/etc/opt/ipf]ls
ipf.conf ipmon.pid ipnat.conf
a2#[/etc/opt/ipf]cat ipf.conf
pass out quick on lo0
pass in quick on lo0
pass out quick on lan0
pass in quick on lan0
pass out quick on lan1
pass in quick on lan1


a2#[/etc/opt/ipf]cat ipnat.conf
map lan1 192.168.0.0/24 -> 218.62.27.254/32 proxy port ftp ftp/tcp
map lan1 192.168.0.0/24 -> 218.62.27.254/32 portmap tcp/udp 10000:20000
map lan1 192.168.0.0/24 -> 218.62.27.254/32

a2#[/etc/opt/ipf]

but why this machine can only proxy one client,
in my lan,only on machine can through the proxy,please help me ,thanks very much!