Some of our PIX (which the problem was not happen in only one PIX) recently found a problem.
In our network environment, the client pc can get reply from pix interface and access the outside internet without any block, but it was found that when the pix get problem, the client was failed to get response from the pix and failed to access the internet also.
Here is the log for the debug arp when:
Success to ping and access internet:
arp-in: rqst for me from 192.168.13.100 for 192.168.13.15, on inside
arp-set: added arp inside 192.168.13.100 0001.9621.ca00 and updating NPs at 1087579650
arp-in: generating reply from 192.168.13.15 0003.6bf6.7980 to 192.168.13.100 0001.9621.ca00
arp-in: request at inside from 192.168.13.100 0001.9621.ca00 for 192.168.13.15 0000.0000.0000
Fail to ping and access internet:
arp-send: arp request built from 192.168.13.15 0003.6bf6.7980 for 192.168.13.100 at 1087826770
arp-in: response at inside from 192.168.13.100 0001.9621.ca00 for 192.168.13.15 0003.6bf6.7980
arp-set: added arp inside 192.168.13.100 0001.9621.ca00 and updating NPs at 1087826770
arp-in: resp from 192.168.13.100 for 192.168.13.15 on inside at 1087826770
arp-send: sending all saved block to inside 192.168.13.100 at 1087826770
The problem was solved when I reboot the PIX and there is not any change for the configuration.