NAT on cisco pix

Posted on 2007-10-09
Medium Priority
Last Modified: 2010-04-09
Hi there,

I am using a CISCO pix 506E as a firewall between a dsl router and my LAN, I would like to get out the the internet using a PC inside the LAN, the problem is; I can't ping the outside interface of the firewall from the PC I can only ping the inside interface. I guess I need to setup NAT? Can someone one help?


Here's the conf

IX Version 6.3(5)
interface ethernet0 auto
interface ethernet1 auto
nameif ethernet0 outside security0
nameif ethernet1 inside security100
access-list inside_access_in permit icmp any any echo-reply log
access-list inside_access_in permit tcp any any
pager lines 24
mtu outside 1500
mtu inside 1500
ip address outside
ip address inside
ip audit info action alarm
ip audit attack action alarm
pdm logging informational 100
pdm history enable
arp timeout 14400
global (outside) 1 interface
nat (inside) 1 0 0
access-group inside_access_in in interface inside
http server enable
http inside
no snmp-server location
no snmp-server contact
snmp-server community public
no snmp-server enable traps
floodguard enable
telnet timeout 5
ssh timeout 5
console timeout 0
dhcpd auto_config outside
terminal width 80
Question by:aaresearch
  • 3
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LVL 79

Accepted Solution

lrmoore earned 1500 total points
ID: 20046238
>I can't ping the outside interface of the firewall from the PC
Correct, and you never will. This is a design "feature" of the PIX.

What you don't have is a default route out...
 route outside

And you can remove the acl from the interface
  no access-group inside_access_in in interface inside

You have restricted outgoing traffic to tcp only, where DNS uses udp and so you have effectively blocked dns. Default behavior is to allow all outgoing traffic without an acl applied.
If you want to be able to ping hosts on the outside, add this:
 access-list icmp_in permit icmp any any echo-reply
 access-group icmp_in in interface outside


Author Comment

ID: 20049732
Thanks for the comment Irmoore, I added those command and still can't ping the router from the inside host any idea? Thanks
LVL 79

Expert Comment

ID: 20051153
I would suggest putting the router in bridge mode and let the PIX get the public IP, but you should be able to get out. What is the router's IP supposed to be? That is the IP that you should use as the route outside.
Can you ping the router from the PIX itself?
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Author Comment

ID: 20052352
I had to add this command
global (outside) 1 netmask
it works now, thanks
LVL 79

Expert Comment

ID: 20052751
You should not have had to add that because you already have this, and it is all you need:
 global (outside) 1 interface

Author Comment

ID: 20055648
I think that did not work because it included the interface IP, may be it's was something else then.


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