Cisco Explorer 4700 Installation Guide download pdf (Page 400)

11-4

Device Manager Guide, Cisco ACE 4700 Series Application Control Engine Appliance

OL-26645-02

Chapter 11 Configuring High Availability

Understanding ACE Redundancy

The election of the active member within each FT group is based on a priority scheme. The member

configured with the higher priority is elected as the active member. If a member with a higher priority

is found after the other member becomes active, the new member becomes active because it has a higher

priority. This behavior is known as preemption and is enabled by default. You can override this default

behavior by disabling preemption. To disable preemption, use the Preempt parameter. Enabling Preempt

causes the member with the higher priority to assert itself and become active. For details about

configuring preemption, see Configuring ACE High Availability Groups, page 11-11.

Stateful Failover

The ACE replicates flows on the active FT group member to the standby group member per connection

for each context. The replicated flows contain all the flow-state information necessary for the standby

member to take over the flow if the active member becomes unresponsive. If the active member becomes

unresponsive, the replicated flows on the standby member become active when the standby member

assumes mastership of the context. The active flows on the former active member transition to a standby

state to fully back up the active flows on the new active member.

Note For the replication process to function properly and successfully replicate the configuration for a user

context when switching from the active context to the standby context, ensure that each user context has

been added to the FT group. All applicable user contexts must be part of an FT group for redundancy to

function properly.

Note By default, connection replication is enabled in the ACE appliance.

After a switchover occurs, the same connection information is available on the new active member.

Supported end-user applications do not need to reconnect to maintain the same network session.

The state information passed to the standby appliance includes the following data

•

Network Address Translation (NAT) table based on information synchronized with the connection

record

• All Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) connections not

terminated by the ACE appliance

• HTTP connection states (Optional)

• Sticky table

Note In a user context, the ACE appliance allows a switchover only of the FT group that belongs to that

context. In the Admin context, the ACE appliance allows a switchover of all FT groups in all configured

contexts in the appliance.

To ensure that bridge learning occurs quickly upon a switchover in a Layer 2 configuration in the case

where a VMAC moves to a new location, the new active member sends a gratuitous ARP on every

interface associated with the active context. Also, when there are two VLANs on the same subnet and

servers need to send packets to clients directly, the servers must know the location of the gateway on the

client-side VLAN. The active member acts as the bridge for the two VLANs. In order to initiate learning

of the new location of the gateway, the new active member sends an ARP request to the gateway on the

client VLAN and bridges the ARP response onto the server VLAN.

1 ... 399 400 401 ... 648

Comments to this Manuals

No comments

Cisco Explorer 4700 Installation Guide Page 400

Comments to this Manuals

Related products and manuals for Digital Video Recorders (DVR) Cisco Explorer 4700