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Cisco ASA Series CLI Configuration Guide
Chapter 1 Setting General VPN Parameters
Understanding Load Balancing
Some Typical Mixed Cluster Scenarios
If you have a mixed configuration—that is, if your load-balancing cluster includes devices running a
mixture of ASA software releases or at least one ASA running ASA Release 7.1(1) or later and a VPN
3000 concentrator—the difference in weighting algorithms becomes an issue if the initial cluster master
fails and another device takes over as master.
The following scenarios illustrate the use of VPN load balancing in clusters consisting of a mixture of
ASAs running ASA Release 7.1(1) and ASA Release 7.0(x) software, as well as VPN 3000 series
concentrators.
Scenario 1: Mixed Cluster with No SSL VPN Connections
In this scenario, the cluster consists of a mixture of ASAs and VPN 3000 concentrators. Some of the
ASA cluster peers are running ASA Release 7.0(x), and some are running Release 7.1(1). The pre-7.1(1)
and VPN 3000 peers do not have any SSL VPN connections, and the 7.1(1) cluster peers have only the
base SSL VPN license, which allows two SSL VPN sessions, but there are no SSL VPN connections. In
this case, all the connections are IPsec, and load balancing works fine.
The two SSL VPN licenses have a very small effect on the user’s taking advantage of the maximum IPsec
session limit, and then only when a VPN 3000 concentrator is the cluster master. In general, the smaller
the number of SSL VPN licenses is on a ASA in a mixed cluster, the smaller the effect on the ASA 7.1(1)
device being able to reach its IPsec session limit in a scenario where there are only IPsec sessions.
Scenario 2: Mixed Cluster Handling SSL VPN Connections
Suppose, for example, an ASA running ASA Release 7.1(1) software is the initial cluster master and then
that device fails. Another device in the cluster takes over automatically as master and applies its own
load-balancing algorithm to determine processor loads within the cluster. A cluster master running ASA
Release 7.1(1) software cannot weight session loads in any way other than what that software provides.
Therefore, it cannot assign a combination of IPsec and SSL VPN session loads properly to ASA devices
running earlier versions nor to VPN 3000 concentrators. Conversely, a VPN 3000 concentrator acting as
the cluster master cannot assign loads properly to an ASA Release 7.1(1) ASA. The following scenario
illustrates this dilemma.
This scenario is similar to the previous one, in that the cluster consists of a mixture of ASAs and VPN
3000 concentrators. Some of the ASA cluster peers are running ASA Release 7.0,(x) and some are
running Release 7.1(1). In this case, however, the cluster is handling SSL VPN connections as well as
IPsec connections.
If a device that is running software earlier than ASA Release 7.1(1) is the cluster master, the master
applies the protocol and logic in effect prior to Release 7.1(1). That is, sessions might be directed to
load-balancing peers that have exceeded their session limit. In that case, the user is denied access.
If the cluster master is a device running ASA Release 7.0(x) software, the old session-weighting
algorithm applies only to the pre-7.1(1) peers in the cluster. No one should be denied access in this case.
Because the pre-7.1(1) peers use the session-weighting algorithm, they are more lightly loaded.
An issue arises, however, because you cannot guarantee that the 7.1(1) peer is always the cluster master.
If the cluster master fails, another peer assumes the role of master. The new master might be any of the
eligible peers. Because of the unpredictability of the results, we recommend that you avoid configuring
this type of cluster.
Summary of Contents for 5505 - ASA Firewall Edition Bundle
Page 28: ...Glossary GL 24 Cisco ASA Series CLI Configuration Guide ...
Page 61: ...P A R T 1 Getting Started with the ASA ...
Page 62: ......
Page 219: ...P A R T 2 Configuring High Availability and Scalability ...
Page 220: ......
Page 403: ...P A R T 2 Configuring Interfaces ...
Page 404: ......
Page 499: ...P A R T 2 Configuring Basic Settings ...
Page 500: ......
Page 533: ...P A R T 2 Configuring Objects and Access Lists ...
Page 534: ......
Page 601: ...P A R T 2 Configuring IP Routing ...
Page 602: ......
Page 745: ...P A R T 2 Configuring Network Address Translation ...
Page 746: ......
Page 845: ...P A R T 2 Configuring AAA Servers and the Local Database ...
Page 846: ......
Page 981: ...P A R T 2 Configuring Access Control ...
Page 982: ......
Page 1061: ...P A R T 2 Configuring Service Policies Using the Modular Policy Framework ...
Page 1062: ......
Page 1093: ...P A R T 2 Configuring Application Inspection ...
Page 1094: ......
Page 1191: ...P A R T 2 Configuring Unified Communications ...
Page 1192: ......
Page 1333: ...P A R T 2 Configuring Connection Settings and QoS ...
Page 1334: ......
Page 1379: ...P A R T 2 Configuring Advanced Network Protection ...
Page 1380: ......
Page 1475: ...P A R T 2 Configuring Modules ...
Page 1476: ......
Page 1549: ...P A R T 2 Configuring VPN ...
Page 1550: ......
Page 1965: ...P A R T 2 Configuring Logging SNMP and Smart Call Home ...
Page 1966: ......
Page 2059: ...P A R T 2 System Administration ...
Page 2060: ......
Page 2098: ...1 8 Cisco ASA Series CLI Configuration Guide Chapter 1 Troubleshooting Viewing the Coredump ...
Page 2099: ...P A R T 2 Reference ...
Page 2100: ......