Box-to-box redundancy enables configuring a pair of routers to act as back up for each other. In the router pair, the active router is determined based on the failover conditions. The router pair continuously exchange status messages. CUBE session information is checkpointed across the active and standby router. This enables the standby router to immediately take over all CUBE call processing responsibilities when the active router becomes unavailable.

A group of redundant interfaces form a Redundancy Group. The active and standby routers are connected by a configurable control link and data synchronization link. The control link is used to communicate the redundancy state for each router. The data synchronization link is used to transfer stateful information to synchronize the stateful database for the calls and media flows. Each pair of redundant interfaces is configured with the same unique ID number, also known as the Redundancy Interface Identifier (RII).

A Virtual IP address (VIP) is configured on interfaces that connect to the external network. All signaling and media is sourced from and sent to the Virtual IP address. External devices such as Cisco Unified Communication Manager, uses VIP as the destination IP address for the calls traversing through Cisco UBE.

The following figure shows the redundancy group configured for a pair of routers with a single outgoing interface.

We recommend that you keep the following in mind when enabling this topology:

• Connect the Cisco CSR 1000v or C8000V running on the server to the virtual switch within the virtualized host. Then connect the virtual switches to external switches using the physical host interfaces. The virtual switch routes the traffic internally between the virtual machines and also connects the external networks.

• Configure high-availability connectivity using redundancy on virtual switch to avoid checkpointing failures.

  In a scenario where the physical switch is down and there is no redundancy configured on virtual switch, the active router continues to process calls as it tracks only the status of virtual switch (which is up). At the same time, the standby router assumes the role of active router as it does not receive keepalive messages from the active router through the physical switch. Hence checkpointing fails. To avoid such scenarios, we recommend you to configure high availability connectivity using redundancy on virtual switch.

• Do not track the switches that are used to connect non-networking end devices or LAN, to determine uplink failures.

• Connect the redundancy group control and data interfaces in the CUBE HA pair to the same physical switch to avoid any latency in the network.

• The RG control and data interfaces of the CUBE HA pair can be connected through a back-to-back cable or using a switch. However, it is recommended to use Portchannel for the RG control and data interfaces for redundancy. A single connection using back-to-back cable or switch presents a single point of failure due to a faulty cable, port, or switch, resulting in error state where both routers are Active.

• If the RG ID is the same for the two different CUBE HA pairs, keepalive interface for check-pointing the RG control and data, and traffic must be in a different subnet or VLAN.

  Note	This recommendation is applicable only if you connect using a switch, not by back-to-back cables.

• You can configure a maximum of two redundancy groups. Hence, there can be only two Active and Standby pairs within the same network.

  Note	This recommendation is applicable only if you connect using a switch, not by back-to-back cables.

• Source all signaling and media from and to the virtual IP address.

• Always save the running configuration to avoid losing it due to router reload during a failover.

• Virtual Routing and Forwarding

  • Define Virtual Router Forwarding (VRF) in the same order on both Active and Standby routers for an accurate synchronization of data.

  • You can configure VRFs only on the traffic interface (SIP and RTP). Do not configure VRF on redundancy group control and data interface.

  • VRF configurations on both the Active and Standby router must be identical. VRF IDs checkpoints for the calls before and after switchover (includes VRF-based RTP port range).

• Manually copy the configurations from one router to the other.

• Replicating the configuration on the Standby router does not commit to the startup configuration; it is the running configuration. You must run the write memory command to commit the changes that are synchronized from the Active router on the Standby router.

The following is a list of further considerations and restrictions you should know before configuring this topology:

• Use Cisco IOS-XE Release 3.11 and or later on both active and standby routers.

• Ensure that you have the required licenses for configuring high availability. For detailed information, see Cisco Unified Border Element Data Sheet.