Pix on Aaron's Worthless Words

Configuring an Active/Passive ASA Pair

Sat, 20 Nov 2010 00:00:00 +0000

A buddy asked for some help on configuring a pair of ASAs in active/passive mode, and, by pure coincidence, my newest project is to set up the same. I’ve done it many time, but it’s one of those things that you don’t really do every day (unless you’re a VAR or something). These things always get covered in rust very quickly in my head, but, once I get one or two details back to the surface, it all comes flooding back. I better take the time to jot down the details.

Using SPF Records To Build Objects

Fri, 16 Oct 2009 00:00:00 +0000

My biggest complain about modern firewalls is their lack of the ability to create rules based on URLs or HTTP streams; you have to open access between IP addresses. Yes, I know there are other means to do that, but I want my ASA/PIX/FWSM to do it without making me do so much work.

Anyway, the fact that you have to use IPs brings up some interesting problems. Let’s say you have a server in a DMZ that needs to query Google for some content. Since you’re a hard-ass network guy like I am, you tell the admin that they have provide the data flow they want to use – source IP, destination IP, protocol, port. They come back and tell you that they need their server to connect via HTTP to 74.125.45.100. You put in the rules as given, but the IP has suddenly changed on you.

Object Groups in the ASA/FWSM/PIX

Thu, 01 Oct 2009 00:00:00 +0000

I can’t believe I haven’t talked about object-groups yet. I had a whole other blog entry written up, and, when I went to link things over, I realized I couldn’t find an intro to it. Here it goes.

Welcome to the modern world. A world of wonder. A world of quickly-advancing technology. A world where clusters of machines sit behind load balancers for scalability and availability. A world where those clusters need access to other clusters. A world where your firewall rulebase gets so big that it’s unreadable without some help.

ASA and Proxy ARP

Fri, 11 Sep 2009 00:00:00 +0000

Wow. A new entry. Everyone sit down before you pass out.

I’ve got a real-world example for you today. We have an ASA 5540 installed at a business unit with interfaces in multiple networks, including one containing the production servers and another containing the accounting servers. The production network sits on a 7600 that’s not ours, so, to avoid IP conflicts, we are statically NATting connections into that network. The 7600 has with many, many VLANs, and, since the firewall production servers are on different VLANs, there’s an interface VLAN between us. Sounds pretty straightforward, but it just wasn’t working when we try to connect between the interfaces.

Port Forwarding on the ASA/FWSM/PIX

Tue, 27 May 2008 00:00:00 +0000

Here’s a simple one since I haven’t updated in a while. I have my ASA 5505 at home and want to forward TCP/80 traffic to my public IP to my webserver at 10.10.10.10. There are two steps here – forward the port and open the ACL.

To forward the port, I would use the static directive, but there are two ways to do that. I can either set up a one-to-one NAT or a port redirection. In the one-to-one NAT, you have a outside address that’s mapped directly to an inside address, and any traffic to that IP is passed to the inside host (if it passes ACLS, of course). One of the limitation, though, of using this setup is that you can’t use that IP as your PAT address, and, since I only have one IP, no other inside hosts would have a outside address to which to be NATted. The other method – port redirection – is a much better solution. In this setup, I actually forward a protocol/port on a outside address to a protocol/port on an inside address. Since there are other ports available on that outside address, the address is still available for other hosts to use as a NAT address.

NAT on a PIX/ASA

Thu, 13 Mar 2008 00:00:00 +0000

NATting sucks and can be confusing. I’m sure everyone agrees to that, but you have to use it at some times. In a PIX/ASA, it’s easy to configure a simple setup, but can be super-complicated in larger networks. In a simple lab, we have set up an ASA with inside and outside interfaces, with the inside as your internal and outside as the Internet.

The NAT setup here is easy.

Commenting Access-lists

Wed, 12 Mar 2008 00:00:00 +0000

There’s a very-overlooked feature of access-lists – the remark. Yes, this is very basic, but it’s worth mentioning, as it has saved me anguish time and time again.

I use remarks to document each line of an ACL (on IOS, PIX, FWSM, ASA, etc.) so that when I go back later, I actually know what I did. They’re simple to use, and, I promise you, you’ll thank yourself for using it when the CTO asks why access to TCP/80 is open from the Internet to the development server.

Can't Login to Your ASA via SSH or Telnet?

Mon, 18 Feb 2008 00:00:00 +0000

I deployed a Cisco ASA at a location and couldn’t get logged in via SSH. I would get prompted, but, no matter what username/password I put in, it would just reject me. After some digging, it turns out that I forgot this command.

aaa authentication ssh console LOCAL

When I put this in, it let me right in as expected. I have no clue what the deal was. I guess I assumed that the ASA would use the local userbase if a AAA service wasn’t configured. I guessed wrong.