Chapter 7 Configuring Redundant ACE Appliances
Overview of Redundancy
7-4
Cisco 4700 Series Application Control Engine Appliance Administration Guide
OL-11157-01
Figure 7-2
shows the uneven distribution of contexts between the two ACEs. As
an example, it is possible that the FT groups A,B, C, and D use only half the
resources that E and F require.
Figure 7-2
Uneven Distribution of Contexts
153640
N=2
# redundant groups
=6
A
B
C
D
E’
F’
A’
B’
C’ D’
E
F
To outside nodes (clients and servers), the active and standby FT group members
appear as one node with respect to their IP addresses and associated VMAC. The
ACE provides active-active redundancy with multiple-contexts only when there
are multiple FT groups configured on each appliance and both appliances contain
at least one active group member (context). With a single context, the ACE
supports active-backup redundancy and each group member is an Admin context.
For details about configuring contexts, see the
Cisco 4700 Series Application
Control Engine Appliance Virtualization Configuration Guide
.
The ACE sends and receives all redundancy-related traffic (protocol packets,
configuration data, heartbeats, and state replication packets) on a dedicated FT
VLAN. You cannot use this dedicated VLAN for normal traffic.
To optimize the transmission of heartbeat packets for multiple FT groups and to
minimize network traffic, the ACE sends and receives heartbeat messages using a
separate process. The ACE uses the heartbeat to probe the peer ACE, rather than
probe each context. When an ACE does not receive a heartbeat from the peer
ACE, all the contexts in the standby state become active. The ACE sends heartbeat
packets over UDP. You can set the frequency with which the ACE sends heartbeat
packets as part of the FT peer configuration. For details about configuring the
heartbeat, see the
“Configuring an FT Peer”
section.
