Cisco ASA Virtual Context Mode

A single Cisco ASA or a cluster of two ASAs can be partition into multiple virtual firewalls known as security contexts. Each context has it’s own independent firewall, with its own security policy, interfaces, and administrators. These contexts are similar to having multiple standalone ASA devices. In combination with failover groups you can run a ASA cluster in active/active state and utilize both devices. Don’t forget when a failover happens that both failover groups need to run on a single device, keep enough ressources free on both devices and do not oversubscribe too much.

You have to look because there are limitation what features are supported in context mode. In version 8 is unsupport to use dynamic routing protocols, VPN, Threat Detection and Quality of Service. In version 9 are some changes and now dynamic routing protocols (not RIP or OSPFv3) and site-to-site IPsec VPNs are supported.

Here the configuration example how to set-up an Cisco ASA 5580 with 10 Gigabit Ethernet interfaces.

Enabling the context mode

mode noconfirm multiple

Physical interface configuration

interface GigabitEthernet4/2 
  description Failover 
  no shutdown 

interface GigabitEthernet4/3 
  description Stateful 
  no shutdown 

interface TenGigabitEthernet5/0 
  description TeTrunk-1st 
  no shutdown 

interface TenGigabitEthernet5/1 
  description TeTrunk-2nd 
  no shutdown 

Redundant interface configuration

interface Redundant 1
  description Redundant-Trunk
  member-interface TenGigabitEthernet5/0
  member-interface TenGigabitEthernet5/1

interface Redundant 1.800
  vlan 800
  description Link-Outside1

interface Redundant 1.801
  vlan 801
  description Link-Outside2

interface Redundant 1.100
  vlan 100
  description Link-Inside1

interface Redundant 1.101
  vlan 101
  description Link-Inside2

interface Redundant 1.500
  vlan 500
  description Link-Management

Here you need to start configuring the ASA failover settings. Like you see in the failover group configuration that I put group 1 to the primary device and group 2 to the seconday device for active/active set-up, when I create the virtual security context I join them to the different failover groups.

failover group 1
  polltime interface 1 holdtime 5

failover group 2
  polltime interface 1 holdtime 5


failover lan unit primary
failover lan interface failover GigabitEthernet4/2
failover interface ip failover standby

failover link stateful GigabitEthernet4/3
failover interface ip stateful standby

failover polltime unit 2 holdtime 6
failover polltime interface 1 holdtime 5
failover timeout 0:00:00

failover active

Failover configuration on the seconday device

interface GigabitEthernet4/2
  description Failover
  no shutdown

failover lan unit secondary
failover lan interface failover GigabitEthernet4/2
failover interface ip failover standby


copy running-config startup-config

Now you start to set-up the virtual contexts and add the interfaces I configured before

admin-context admin-asa-01

context admin-asa-01
  allocate-interface Redundant1.500 Link-Management
  config-url disk0:/admin-asa-01.conf
  join-failover-group 1

context virtual-asa-02
  allocate-interface Redundant1.800 Link-Outside1
  allocate-interface Redundant1.100 Link-Inside1
  config-url disk0:/virtual-asa-02.conf
  join-failover-group 1

context virtual-asa-03
  allocate-interface Redundant1.801 Link-Outside2
  allocate-interface Redundant1.101 Link-Inside2
  config-url disk0:/virtual-asa-03.conf
  join-failover-group 2

In the end save the configuration

write memory all

Afterwards you can change to the configured contexts with the command

changeto context virtual-asa-02

and start configuring your virtual firewalls.

Uptime – simple http monitoring utility

I found an very interesting http monitoring tool called Uptime using node.js and mongoDB. I directly installed Uptime on one of my Linux servers and from the first look I find it really cool 🙂 before you start you need to get node.js and mongoDB installed on your server and the rest is then very easy.

Ones the Uptime is running you can access the web interface and create the first checks, here some screenshots:

Here you create your http checks and define some settings:

Detailed check overview with graphs:

If you are interested then have a look here:

Cisco SSL VPN Configuration

At the moment I play around with Cisco SSL VPN (WebVPN) and here some steps how to configured these on an Cisco ASA. SSL VPN is on one hand the Cisco Anyconnect client and on the other an Clientless SSL VPN over a portal what is running on the ASA.

I will not go into much detail here, it’s more basic configurations steps you need to configure to get it running.

For a basic set-up we need two network objects

object network inside-subnet  

object network sslvpn-subnet  

Then we define the DHCP pool for Anyconnect connections

ip local pool SSLVPNClientPool mask

We also need to make sure that Anyconnect clients communication with their original IP address and for that we need the following nat statement

nat (inside,outside) source static inside-subnet inside-subnet destination static sslvpn-subnet sslvpn-subnet

Here you select the Anyconnect package what you need to upload to your flash before and enable webvpn on your outside interface

  anyconnect image disk0:/anyconnect-win-2.4.1012-k9.pkg 1  
  enable outside  
  anyconnect enable  

In the SSL VPN client policy we define name server, domain name and DHCP pool. We also define here Anyconnect with ssl-client and the portal with ssl-clientless

group-policy SSLVPNClientPolicy internal 
group-policy SSLVPNClientPolicy attributes  
  dns-server value  
  default-domain value  
  address-pools value SSLVPNClientPool  
  vpn-tunnel-protocol ssl-client ssl-clientless  

We configure an SSL VPN tunnel group for remote access and set default policy to the SSL VPN client policy we configured in the step before

tunnel-group SSLVPNClientProfile type remote-access 
tunnel-group SSLVPNClientProfile general-attributes  
  default-group-policy SSLVPNClientPolicy  

Next, we define an external aaa server in my example an Windows Active Directory

aaa-server ldap-group protocol ldap
  aaa-server ldap-group (inside) host   
  ldap-base-dn OU=Departments, OU=DE, OU=Company, DC=domain,DC=com   
  ldap-login-dn cn=LDAPReader, OU=ServiceAccounts, OU=Company, DC=domain, DC=com   
  ldap-login-password secretpassword   
  ldap-naming-attribute sAMAccountName   
  ldap-scope subtree   
  server-type microsoft   

After we configured the external aaa server we need to link that in the tunnel group

tunnel-group SSLVPNClientProfile webvpn-attributes  
  group-alias SSLVPNClient enable  
  authentication-server-group ldap-group  

One of the last steps we enable the tunnel group within webvpn and configure sysopt permit-vpn

  tunnel-group-list enable  
sysopt connection permit-vpn

With the following command you can enable NTLM for a whole subnet if you use Windows IIS and integrate authentication

auto-signon allow ip auth-type ntlm

That’s it, quite easy and clear setup over the command line, you can also click yourself through the ASDM but it will definitively take longer.

Strange VPN behaviour between Juniper ISG and ASA

Always something new what is not working, this time a site-to-site VPN tunnel between a Juniper ISG 2000 and a Cisco ASA 5520. After the initial set-up what a colleague did everything seemed to work fine with the VPN, the tunnel come up and communication was possible. What my colleague not did was to do some intensive testing and check in detail the configuration.

The problems began ones these VPN tunnels were used for production traffic, they worked fine for some hours or maybe days but then suddenly you were not able to send or receive any data over the tunnel and mostly it happen over night where it was difficult to troubleshoot. In the beginning everybody said that it was a problem within the internet but when it happened three or four times a week I got suspicious that its something wrong with the boxes or even configuration.

First thing was to check the configuration and quickly I found a difference in the IPSec Phase2 default timers, the Juniper uses 1 hour and Cisco has 8 hours. I was happy and thought I found the reason for the connectivity problems but then two days later it happened again… 🙁

There where some strange syslog messages about anti-replay checking failed:

ASA-4-402119 IPSEC: Received an ESP packet (SPI= 0xFBEFD496, sequence number= 0x1C24) from (user= to that failed anti-replay checking.

These messages always came when we had the connectivity problems and that could be only now the last reason. I have to say I didn’t really found much but there were some articles that Juniper doesn’t support Cisco Anti-Replay checking and that you need to disable that on the Cisco side.

Here a release note I found from Juniper but it’s about Cisco’s GET VPN:

In the end that was the only thing I found and I thought give it a try and disable the anti-replay checking on the ASA when we had the problems again. I did so I waited until the problem happened again and disable the anti-replay checking with the following command:

crypto ipsec security-association replay disable

It’s global command were you disable the checking for the whole device. Here some more information:

When I disabled the checking the communication was suddenly possible again and since then the problem never happened again so the anti-replay checking was the cause of the connection problems between the Juniper and the Cisco. Always something new to learn 🙂