Firewall Wizards mailing list archives
Re: PIX access-list help
From: "Fetch, Brandon" <bfetch () tpg com>
Date: Tue, 25 Dec 2007 17:13:50 -0500
Easiest thing to remember is any communication is allowed from a higher security interface to a lower security one (inside to outside, inside to DMZ, DMZ to outside) unless explicitly prevented. Next thing is to remember the application of ACLs is from the physical interface's perspective. You create an ACL and apply it either in or out of the interface. Preventing packets from leaving that network, ie coming "in" to the interface, are applied "access-group in interface blah". To prevent packets from entering that network, ie going "out" to that interface, are applied "access-group out interface blah". Allowing packets from the Internet to a DMZ host requires two items: A "static" configuration line mapping for the outside IP & port to the internal IP & port. A inbound ACL applied "in" on the outside interface. In your particular case it sounds like a minor change of your ACL and the application in the opposite direction on the DMZ interface would fix the problem. Some examples: static (DMZ,outside) tcp 22.22.22.22 http 10.10.10.10 http netmask 255.255.255.255 0 0 static(DMZ, outside) tcp 22.22.22.23 smtp 10.10.10.11 smtp netmask 255.255.255.255 0 0 access-list inbound permit tcp any 22.22.22.22 eq http access-list inbound permit tcp any 22.22.22.23 eq smtp access-group inbound in interface outside (allow web access to 22.22.22.22 & SMTP to .23 from the Internet) access-list DMZ-to-inside permit tcp host 10.10.10.11 192.168.1.11 eq smtp access-group DMZ-to-inside in interface DMZ (allow SMTP from DMZ-10.10.10.11 to inside-192.168.1.11) To prevent outbound from the inside network to either Internet or DMZ you can apply an ACL "out" on the inside interface. access-list inside-out permit any any eq http access-list inside-out permit any any eq 443 access-list inside-out permit any 192.168.1.11 eq smtp access-group inside-out in interface inside (This will only allow outbound HTTP/S & SMTP to either the Internet or DMZ) You can also help lock-down any packet leakage by applying an outbound ACL to our outside interface to allow only what you want leaving your network. Remembering to do both sides of the firewall is a good security practice overall. HTH, Brandon -----Original Message----- From: firewall-wizards-bounces () listserv icsalabs com [mailto:firewall-wizards-bounces () listserv icsalabs com] On Behalf Of Brian Blater Sent: Friday, December 21, 2007 11:02 AM To: FW Wiz Subject: [fw-wiz] PIX access-list help I'm a little befuddled with PIX access lists and need some help and understanding. I have a PIX 515 version 6.3(3) with 3 interfaces - outside, inside, dmz. Up til now I have only been using the outside and inside interface. I have started configuring the dmz interface and have set it at security50 (outside = 0, inside = 100). I currently have only an access-list on the outside interface allowing some specific traffic in to the inside network. Right now the inside and dmz can talk to the internet just fine and the inside can talk to the dmz network fine. However, I want to implement an access-list on the dmz interface and this is where the problems start. If I assign an access list to the dmz port to allow smtp from a dmz host to the inside mail server I no longer have communication to the internet from the dmz and the inside cannot talk to the dmz because of the implicit deny of the access list. So, my main question, is there an access list command I can have that basically says "allow all communication from the dmz to the internet" and one that says "allow communication from the inside to the dmz"? I know I can add "access-list dmz permit ip host 192.168.1.1 any" and that solves the problem of getting to the internet, but then it opens all communication to the inside from this host and I don't want to do that. Since this is version 6.3(3) I can't use an out access-list which I think might solve the problem. I have enough memory to run version 7.x on this PIX, but I'm trying to tackle one problem at a time and I'm a little hesitant about doing the 7.x upgrade just yet. I have more questions, but I think I start here for now and ask the other questions when they are more relevant. Thanks for your help, Brian _______________________________________________ firewall-wizards mailing list firewall-wizards () listserv icsalabs com https://listserv.icsalabs.com/mailman/listinfo/firewall-wizards This message is intended only for the person(s) to which it is addressed and may contain privileged, confidential and/or insider information. If you have received this communication in error, please notify us immediately by replying to the message and deleting it from your computer. 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Current thread:
- PIX access-list help Brian Blater (Dec 24)
- Re: PIX access-list help Fetch, Brandon (Dec 26)
- Re: PIX access-list help Fetch, Brandon (Dec 26)
- Re: PIX access-list help Farrukh Haroon (Dec 26)
- Re: PIX access-list help kevin horvath (Dec 26)
- Re: PIX access-list help Paul Melson (Dec 26)
- Re: PIX access-list help Brian Blater (Dec 26)
- Re: PIX access-list help Avishai Wool (Dec 26)