ASA Remote Access User Prevent SSH Access

When configuring a remote access VPN on an ASA, there are times when an external authentication server (RADIUS, TACACS+, etc) is not available.  In this case, the local AAA database can be used:

asa01(config)# username vpnuser password p@ssw0rd privilege 0
asa01(config)# username vpnuser attributes
asa01(config-username)# service-type remote-access
asa01(config-username)# exit
asa01(config)#

You might think that specifying privilege 0 and service-type remote access as shown above would be enough to prevent this user from logging in through SSH.  However, this may not be the case.  Let's look at the following example:

asa01# sh run user vpnuser
username vpnuser password jpCK6VfivhvBp0Pn encrypted privilege 0
username vpnuser attributes
 service-type remote-access
asa01# sh run aaa
aaa authentication ssh console LOCAL
aaa authorization exec LOCAL
asa01#

With this configuration, it is still possible for "vpnuser" to log in through SSH:

vpnuser@asa01's password:
login as: vpnuser
vpnuser@asa01's password:
Type help or '?' for a list of available commands.
asa01>

This is possible because the above configuration only specifies AAA authentication, not authorization.  Therefore the local user account's password is checked against the local database, but no check is performed to determine whether or not this local user is authorized for EXEC shell access.  This behavior can be changed by enabling management authorization with the following command:

asa01(config)# aaa authorization exec LOCAL
asa01(config)#

Now if we attempt to log in with this same account, the login will fail:

login as: vpnuser
vpnuser@asa01's password:
Access denied
vpnuser@asa01's password:

The ASA configuration guide goes into more detail about this feature here:
http://www.cisco.com/c/en/us/td/docs/security/asa/asa91/configuration/general/asa_91_general_config/admin_management.html#86134

Choosing an ExtremeXOS Software Release

When updating ExtremeXOS, it is important to choose your software release carefully.  The newest builds may contain new features that are not yet stable.  I learned this the hard way.  The Extreme support portal currently does not label their software builds with anything that indicates what is a stable build and what is may contain new unstable features.

Extreme Networks EXOS Cheat Sheet

After working in primarily Cisco or Cisco-esque CLIs, ExtremeXOS can have a bit of a learning curve.  At the time of this post, Extreme Networks' documentation is almost entirely in PDFs.  In my opinion, these are a bit of a pain to navigate and are not well indexed by search engines.

This post is meant to serve as a basic EXOS cheat sheet.  It is by no means meant to be a configuration guide or thorough command reference.  I will update this post periodically to add additional commands.

update: I reached out to Extreme regarding their documentation (I work for a partner), and it turns out they already have an EXOS cheat sheet, so my channel SE sent it over.  I was not able to find this document anywhere on Extreme's site.  However, an Extreme SE confirmed this document is public, so here it is:  EXOS Quick Guide - Cheat Sheet.  I may still update this page on occasion, but Extreme's document is more complete.

HOWTO: Basic Cisco ASA AnyConnect VPN 8.2(5)

A while back I posted a how-to for configuring AnyConnect in ASA version 8.3+.  I recently received a request to post the 8.2(5) configuration, so here it is.  The example below uses split tunneling and local authentication.  For RADIUS authentication, see this post.

Before beginning, verify you have the AnyConnect essentials license (without this license, only two simultaneous sessions are permitted).

asa# sh ver | inc AnyConnect
AnyConnect Premium Peers          : 25             perpetual
AnyConnect Essentials             : 25             perpetual
AnyConnect for Mobile             : Enabled        perpetual
AnyConnect for Cisco VPN Phone    : Enabled        perpetual
asa#

HOWTO: Cisco ASA AnyConnect RADIUS Authentication with NPS

Following up on my previous AnyConnect how-to, this post shows how to configure a Cisco ASA to authenticate against a Windows Network Policy Server (NPS) using RADIUS.

First, configure a aaa-server group with the radius protocol.

asa01(config)# aaa-server RADIUS protocol radius
asa01(config-aaa-server-group)# exit
asa01(config)#

Next, specify your NPS server and pre-shared-key.

asa01(config)# aaa-server RADIUS (inside) host 10.24.12.2
asa01(config-aaa-server-host)# key pr3-shar3d-k3y
asa01(config-aaa-server-host)# exit
asa01(config)#

On your NPS server, launch NPS.

HOWTO: Basic Cisco ASA AnyConnect VPN 8.3+

This is a brief how-to style guide for configuring an AnyConnect remote access VPN on an ASA running version 8.3(1) or greater.  The example below uses split tunneling and local authentication.  RADIUS authentication will be covered in a future post. (update: see here)

Before beginning, verify you have the AnyConnect essentials license (without this license, only two simultaneous sessions are permitted).

asa# sh ver | inc AnyConnect
AnyConnect Premium Peers          : 25             perpetual
AnyConnect Essentials             : 25             perpetual
AnyConnect for Mobile             : Enabled        perpetual
AnyConnect for Cisco VPN Phone    : Enabled        perpetual
asa#

ASA pre-8.3 vs post-8.3 NAT explained

In ASA software version 8.3(1), Cisco completely restructured ASA NAT syntax.  Quite a bit has already been written about these changes. However, since this is often a cause of confusion, I will try to provide an explanation of three of the most commonly used forms of NAT on an ASA: dynamic PAT, static NAT, and "nonat."  Below you'll find pre-8.3 and post-8.3 configuration examples with translations into into plain English.  Please feel free to comment if you have any questions.

What is NAT?

I'll start with the basics.  NAT stands for network address translation.  It translates the real IP address of a device to the mapped IP and vice versa.

Real IP: the actual IP address of the device generating the traffic (on the inside interface in the examples below)
Mapped IP: the IP address the ASA translates the real IP address to (on the outside interface in the examples below).

NAT is most often used to translate private RFC 1918 IP addresses to publicly routable IP addresses (there are other less common uses as well).

For example:
A ping is sent from TestVM (192.168.10.2) to R1 (72.163.4.166).  In this example, R1 is on the internet, so the ASA cannot route the private address of 192.168.10.2 to R1.  It must NAT the packet.

We can see this happen in the Wireshark captures below: