asa failover

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Cisco ASA Active/Standby Failover ConfigurationThe security appliance supports two failover configurations:Active/ActiveFailover and Active/Standby

Failover. Each failover configuration has its own method to determine and perform failover. With

Active/Active Failover, both units can pass network traffic. This lets you configure load balancing on

your network.Active/ActiveFailover is only available on units that run in multiple context mode. With

Active/Standby Failover, only one unit passes traffic while the other unit waits in a standby state. If

Active unit fails, secondary will take over and starts forwarding the traffic. When Secondary becomes

active, it will also change it's interface IP address and mac address as well. In Active/Standby

configuration, virtually all of the configuration from the active unit is replicated to the secondary unit

through a failover cable.

This article focuses on how to configure an Active/Standby Failover in ASA Security Appliance.

PrerequisitesHardware Requirements

The two units in a failover configuration must have the same hardware configuration. They must be the

same model, have the same number and types of interfaces, and the same amount of RAM.

License Requirements

Failover units do not require the same license on each unit.

Older versions of adaptive security appliance software required that the licenses match on each unit.

Starting with Version 8.3(1), you no longer need to install identical licenses. Typically, you buy a license

only for the primary unit; for Active/Standby failover, the secondary unit inherits the primary license

when it becomes active. If you have licenses on both units, they combine into a single running failover

cluster license.

How Failover Licenses Combine (examples)

If you have two ASA 5540 adaptive security appliances, one with 20 contexts and the other with

10 contexts; the combined license allows 30 contexts. For Active/Active failover, for example, one unit

can use 18 contexts and the other unit can use 12 contexts, for a total of 30; the combined usage cannot

exceed the failover cluster license.

If you have 48 weeks left on the Botnet Traffic Filter license on both units, then the combined

duration is 96 weeks.

If you have two ASA 5520 adaptive security appliances with 500 SSL VPN sessions each; because

the platform limit is 750, the combined license allows 750 SSL VPN sessions.

Now let's dive in to the configuration of Active-Standby Failover. In this document we will be using the

Cisco ASA with image of version 8.4(x) and topology as described in the below image.
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!

interface GigabitEthernet2

nameif DMZ

security-level 50

ip address 10.0.0.1 255.255.255.0 standby 10.0.0.2

! Tell the ASA that G3 will be named "LAN_FAIL" and that it will be used

! to replicate the configuration between ASA1 and ASA2

failover lan interface LAN_FAIL GigabitEthernet3

! Use the failover command to assign "LAN_FAIL" the active

! and standby IP addresses

failover interface ip LAN_FAIL 10.1.1.1 255.255.255.252 standby 10.1.1.2

! Tell the ASA that G4 will be named "LINK_FAIL" and assign the IP address for active

! and standby. Note that the word 'link' is the clue to identify this as the stateful connection

failover link LINK_FAIL GigabitEthernet4

failover interface ip LINK_FAIL 10.2.2.1 255.255.255.252 standby 10.2.2.2

! Tell this ASA that it's title will be "PRIMARY"

failover lan unit primary

! Enable failover

failover

On the standby unit, we just need to do the following configuration, and the rest will be automaticallyreplicated from the Active device.

ASA2

interface GigabitEthernet3

no shutdown


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!

failover lan interface LAN_FAIL GigabitEthernet3

failover interface ip LAN_FAIL 10.1.1.1 255.255.255.252 standby 10.1.1.2

!

failover

Optional ConfigurationThe above configuration is enough to run failover on ASA devices, but you could additionally configure

some optional parameters for extra features.

Optionally, also replicate the HTTP sessions

failover replication http

Change the prompt to show Primary or Secondary and Active or Standby.

prompt hostname priority state

After configuring the prompt, the prompt on ASA devices will look like this:

ASA1/pri/act#

ASA1/sec/stby#

Note that the default hostname will be the same for both active and standby units, due to the

configuration being replicated.

Enable failover shared secret

failover key *****

In the lab provided if you want to ping the outside hosts, you might need to apply an access-list at

outside interface to permit icmp replies to inside hosts or you can also create the following inspection

policy for icmp inspection.

class-map INSPECT_ICMPmatch any

!

policy-map global_policy

class INSPECT_ICMP

inspect icmp


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The ARP table

The Layer 2 bridge table (when it runs in the transparent firewall mode)

The HTTP connection states (if HTTP replication is enabled)

The ISAKMP and IPSec SA table

The GTP PDP connection database

The information that is not passed to the standby unit when stateful failover is enabled includes these:

The HTTP connection table (unless HTTP replication is enabled)

The user authentication (uauth) table

The routing tables

State information for security service modules

'show ip address' command on Cisco ASA

In the show ip address command, we can see that the IP address are shown twice. Now you may

wonder, why it is showing twice?

First section is "System IP Addresses" and the Second section is "Current IP Addresses".

In the above scenario, in case the Primary ASA fails, we can observe that ASA2 which is now Active ASA,

will show the System IP addresses as the IPs configured manually on it's physical interfaces, and the

Current IP addresses will be of the ASA1 interface IP addresses, which the firewall is using currently.

The "active" unit uses the "system" IP addresses and the "standby" unit uses the "standby" addresses. If

failover happens, the normal routed interfaces on the new active unit will use the system IP address.

The addresses configured on the lan and stateful failover links do not change or swap.

asa failover

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