pix的nat0下为何内网ping不出去？
实验环境为：一台PC（192.168.254.2）接PIX的inside（192.168.254.1），PIX的outside（192.168.20.5）接192.168.20.0/24网络的交换机，内网网关为PIX的inside，外网网关为192.168.20.1。用nat 0模式。
现象为：在PIX上ping 192.168.20.1通，ping192.168.254.2也通，但在PC上ping 192.168.20.1却不通。
PIX的配置为：
PIX Version 5.1(2)
nameif ethernet0 outside security0
nameif ethernet1 inside security100
enable password 8Ry2YjIyt7RRXU24 encrypted
passwd 2KFQnbNIdI.2KYOU encrypted
hostname pixfirewall
fixup protocol ftp 21
fixup protocol http 80
fixup protocol h323 1720
fixup protocol rsh 514
fixup protocol smtp 25
fixup protocol sqlnet 1521
names
access-list 101 permit ip 192.168.254.0 255.255.255.0 any
pager lines 24
logging on
no logging timestamp
no logging standby
no logging console
no logging monitor
no logging buffered
no logging history
logging facility 20
logging queue 512
interface ethernet0 auto
interface ethernet1 auto
mtu outside 1500
mtu inside 1500
ip address outside 192.168.20.5 255.255.255.0
ip address inside 192.168.254.1 255.255.255.0
no failover
failover timeout 0:00:00
failover ip address outside 0.0.0.0
failover ip address inside 0.0.0.0
arp timeout 14400
nat (inside) 0 access-list 101
conduit permit icmp any any
route outside 0.0.0.0 0.0.0.0 192.168.20.1 1
timeout xlate 3:00:00 conn 10:00:00 half-closed 0:10:00 udp 0:02:00
timeout rpc 0:10:00 h323 0:05:00
timeout uauth 0:05:00 absolute
aaa-server TACACS protocol tacacs
aaa-server RADIUS protocol radius
no snmp-server location
no snmp-server contact
snmp-server community public
no snmp-server enable traps
floodguard enable
isakmp identity hostname
telnet 192.168.254.0 255.255.255.0 inside
telnet timeout 5
terminal width 80
Cryptochecksum:d41d8cd98f00b204e9800998ecf8427e
