# CUBE high availability Canonical: https://warmtransfer.net/knowledge/cube-high-availability Last verified: 2026-09-25 Cisco Unified Border Element (CUBE) box-to-box redundancy uses the Redundancy Group (RG) infrastructure to maintain session state between paired routers[^5]. All signaling and media are bound to Virtual IP (VIP) addresses configured on externally facing interfaces, ensuring consistent addressing across switchovers[^56]. ## Redundancy Group Architecture In a CUBE HA pair, the RG infrastructure relies on two interconnecting paths: a control link carrying the redundancy state of each router and a data synchronization link carrying stateful call and media-flow information[^40]. The RG infrastructure component uses an HSRP-like protocol exchanging keepalive and hello messages to negotiate redundancy state, alongside a dedicated transport to checkpoint call signaling and media state[^41]. Prerequisites and interface configuration rules include: - A Layer 2 connection between the active and standby routers, as well as NTP or identical clocks on both devices[^36]. - Cisco recommends using port channels for the RG control and data interfaces because a single cable or switch path constitutes a single point of failure that can leave both routers in an Active state[^35]. - Cisco recommends connecting the RG control and data interfaces of the pair to the same physical switch to avoid network latency[^42]. - One CUBE in the HA pair must have the lower IP address on all 3 interfaces compared with the peer router's corresponding interfaces[^24]. - Secondary IP addresses are not permitted on CUBE HA interfaces[^29]. - Both routers must be configured with the same redundancy group priority and failover threshold[^45]. - VRFs must be defined identically and in the same order on both active and standby routers for accurate data synchronization[^57]. - Up to 2 active/standby CUBE HA pairs (2 redundancy groups) may exist on the same Layer 2 segment, with a unique Redundancy Interface Identifier (RII) per redundant interface pair[^54]. VIPs are configured on each redundant interface using the command syntax `redundancy group ip
exclusive`[^55]. External devices such as Cisco Unified Communications Manager must target the CUBE HA VIP address rather than physical interface addresses[^34]. Interface tracking of the LAN and WAN interfaces (for example track 1 interface... line-protocol) is assigned to the redundancy group so that traffic-interface failure triggers switchover.[^51] ## Call State Checkpointing and Feature Restrictions CUBE HA checkpoints only active calls that have completed a 200 OK/ACK transaction[^8]. Calls still in transit, including those in trying or ringing states, are not checkpointed[^52]. A media inactivity timer allows the HA pair to disconnect calls when no RTP is received within a configured period, such as via `timer receive-rtp 1200`[^25]. Transport-layer sessions using TCP, TLS, and UDP are not checkpointed between the HA pair[^53]. Following a failover, SIP-layer signaling state is preserved, but remote user agents must re-establish TCP sessions before sending further messages[^49]. Out-of-band DTMF using SIP NOTIFY or KPML is not supported on a call after switchover[^33]. The following features and co-located roles are not preserved or supported: - SCCP-based media resources, CPA, noise reduction, acoustic shock protection, and transrating calls are not preserved or supported across a switchover[^32]. - Media flow-around and the UC Services API are not supported with box-to-box HA[^28]. - Co-locating Unified SRST or TDM gateway functions on the HA routers is not supported[^30]. ## Failover Behavior and Operational Lifecycle Upon failover, the previously active router reloads by design[^37]. Any router that is reloaded while in a CUBE HA relationship boots up as Standby[^39]. Configuration changes carry specific lifecycle considerations: - After completing CUBE HA configuration, the configuration must be saved and the router reloaded[^38]. - Adding or removing the `redundancy-group` command under `voice service voip` requires a reload to take effect[^43]. - Configuration replicated from the active router lands only in the standby router's running configuration and must be committed on the standby using `write memory`[^48]. ## Platform Deployments and Licensing CUBE box-to-box redundancy is supported on Cisco 4000 Series ISRs and Catalyst 8300, 8200, and 8200-L Edge Platforms[^5]. On ASR 1000 Series routers, box-to-box redundancy is supported on the ASR 1001-X, 1002-X, 1004, 1006, and 1006-X starting in Cisco IOS XE 3.11[^3]. The ASR 1006 supports both inbox and box-to-box redundancy, but cannot switch between the 2 modes dynamically[^27]. ASR 1000 box-to-box HA additionally requires the Firewall/NAT Stateful Inter-Chassis Redundancy license FLSASR1-FWNAT-R[^4]. When deploying with Cisco Application Centric Infrastructure (ACI), Cisco advises placing an intermediate Layer 3 switch between the CUBE HA pair and the ACI fabric so that ACI does not directly learn the CUBE IP and MAC addresses[^1]. WAN links cannot be terminated directly on a CUBE HA router[^31]. Both CUBE HA routers must reside in the same data center; geographic stateful switchover and routers connected across MAN Ethernet are not supported[^44]. For virtualized and cloud environments: - For C8000V HA, the virtual router connects to the virtual switch within the virtualized host, and the RG control and data interfaces may be connected back-to-back or through a switch[^7]. - CUBE HA is not supported on vCUBE deployed in AWS or Microsoft Azure[^26]. For Smart Licensing: - Both platforms of a box-to-box HA pair must establish trust with the same Cisco Smart Software Manager (CSSM) Smart Virtual Account[^46]. - Only the active platform submits license usage reports to CSSM; a newly active platform starts a new measurement interval[^2]. - From Cisco IOS XE Amsterdam 17.2.1r, CUBE license usage in HA deployments is based on dynamic call counting[^11]. - Inbox high availability under Smart Licensing requires CUBE Trunk Standard Session licenses[^18]. ## Webex Calling and Webex Contact Center Integrations Deploying CUBE HA as a Webex Calling Local Gateway requires Cisco IOS XE 17.9.1 or later on a platform supporting both roles[^22]. Configuration across both CUBEs in the pair must be identical, including the physical setup[^21]. Cisco recommends retaining the default RG timers (delay 30 seconds and reload 60 seconds) with a holdtime at least 3 times the hellotime[^20]. Once HA is configured, Local Gateway configuration—whether registration-based or certificate-based—is applied on both routers[^23]. For Webex Contact Center, component-redundancy guidance requires peer CUBEs to use the same hardware, software configuration, and IOS version, using VIPs for signaling and media[^58]. ## Verification Operational status is verified using EXEC mode show commands: - `show redundancy application group all` indicates healthy operation when one router reports `My Role ACTIVE` and `Peer RF state STANDBY HOT`[^12]. - `show redundancy application if-mgr group ` confirms the VIP interface state as `no shut` on the active router and `shut` on the standby router[^14]. ## Applicability Support for IPv6 flows in CUBE high availability requires Cisco IOS XE Dublin 17.12.1a or later[^19]. Cisco TAC tech note 221645 demonstrates CUBE HA on ASR 1001-X routers running Cisco IOS XE 16.09.04[^50]. Box-to-box redundancy on ASR 1000 Series platforms applies from Cisco IOS XE 3.11 onwards[^3]. Deployments as a Webex Calling Local Gateway require Cisco IOS XE 17.9.1 or later[^22]. ## What remains uncertain Trunk Redundant Session versus Enhanced Trunk license naming across product eras is not covered by the sources below. Measured failover and media interruption durations are not covered by the sources below. The software upgrade procedure for an HA pair, including router order and call impact, is not covered by the sources below. Webex Local Gateway SIP registration and TLS behavior during a switchover is not covered by the sources below. Deploying CUBE HA on Google Cloud Platform or other public clouds, as well as on-premises hypervisor specifics, is not covered by the sources below. Non-HA multi-CUBE redundancy across separate sites using OPTIONS keepalives and dial-peer groups is not covered by the sources below. The manual switchover command (`redundancy application reload group n self`) for failover testing is not covered by the sources below. DSP high availability support for transcoding across HA pairs is not covered by the sources below. ## Sources [^1]: Cisco advises placing an intermediate Layer 3 switch between a CUBE HA pair and an ACI fabric so ACI does not directly learn the CUBE IP and MAC addresses. Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - High Availability on Cisco 4000 Integrated Services Routers and Cisco Catalyst 8000 Series Edge Platforms](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/m-cube-ha-isr-g3.html), ACI deployment note. Checked 2026-09-25. [^2]: In box-to-box CUBE HA only the active platform submits license usage reports to CSSM, and a newly active platform starts a new measurement interval. Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - Smart Licensing](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/m_smart_licensing.html), Smart Licensing / Box-to-Box High Availability. Checked 2026-09-25. [^3]: On ASR 1000, CUBE box-to-box redundancy is supported on ASR 1001-X, 1002-X, 1004, 1006 and 1006-X from IOS XE 3.11. Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - High Availability on Cisco ASR 1000 and Cisco Catalyst 8000 Series Routers](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/m-cube-ha-asr.html), Box-to-Box Redundancy supported platforms. Checked 2026-09-25. [^4]: On ASR 1000, CUBE box-to-box HA additionally requires the Firewall/NAT Stateful Inter-Chassis Redundancy license FLSASR1-FWNAT-R. Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - High Availability on Cisco ASR 1000 and Cisco Catalyst 8000 Series Routers](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/m-cube-ha-asr.html), Prerequisites / licensing. Checked 2026-09-25. [^5]: CUBE box-to-box redundancy is supported on Cisco 4000 Series ISRs and Catalyst 8300, 8200 and 8200-L Edge Platforms and uses the Redundancy Group (RG) infrastructure. Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - High Availability on Cisco 4000 Integrated Services Routers and Cisco Catalyst 8000 Series Edge Platforms](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/m-cube-ha-isr-g3.html), Chapter introduction / Box-to-Box Redundancy. Checked 2026-09-25. [^6]: Under CUBE Smart Licensing, box-to-box high availability requires CUBE Trunk Redundant Session licenses (disputed). Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - Smart Licensing](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/m_smart_licensing.html), Smart Licensing / Box-to-Box High Availability. Checked 2026-09-25. [^7]: For C8000V HA the virtual router connects to the virtual switch within the virtualized host, and the RG control and data interfaces may be connected back-to-back or through a switch. Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - High Availability on Cisco C8000V Series Cloud Services Routers](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/m-cube-ha-csr.html), Connection topology. Checked 2026-09-25. [^8]: CUBE HA checkpoints only active calls, meaning calls connected with a completed 200 OK/ACK transaction. Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - High Availability on Cisco 4000 Integrated Services Routers and Cisco Catalyst 8000 Series Edge Platforms](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/m-cube-ha-isr-g3.html), Restrictions / checkpointing list. Checked 2026-09-25. [^9]: The documented CUBE box-to-box sequence is: configure the redundancy group with control and data interfaces, interface tracking, redundancy interfaces with RIIs and VIPs, SIP binding, redundancy-group under voice service voip, media inactivity timer, save and reload, then configure the peer and point external devices at the VIP. Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - High Availability on Cisco 4000 Integrated Services Routers and Cisco Catalyst 8000 Series Edge Platforms](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/m-cube-ha-isr-g3.html), Configuring box-to-box redundancy (numbered procedure). Checked 2026-09-25. [^10]: The CUBE 14 datasheet states that CUBE high availability requires an Enhanced Trunk or Media proxy session license (disputed). Source: [Cisco Unified Border Element Version 14 Data Sheet](https://www.cisco.com/c/en/us/products/collateral/unified-communications/unified-border-element/data-sheet-c78-729692.html), High availability row of the features table. Checked 2026-09-25. [^11]: From Cisco IOS XE Amsterdam 17.2.1r, CUBE license usage in HA deployments is based on dynamic call counting. Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - Smart Licensing](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/m_smart_licensing.html), Smart Licensing / High Availability subsections. Checked 2026-09-25. [^12]: In show redundancy application group all a healthy pair shows My Role ACTIVE on one router with Peer RF state STANDBY HOT. Source: [Implement CUBE high availability as Local Gateway](https://help.webex.com/en-us/article/ndiofhf/Implement-CUBE-High-Availability-as-Local-Gateway), Configure redundancy on both CUBEs (verification output). Checked 2026-09-25. [^13]: CUBE HA troubleshooting uses debug voice high-availability all and debug voip rtp high-availability, and show voice high-availability summary is referenced for voice HA status. Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - Stateful Switchover Between Redundancy Paired Intra or Inter-box Devices](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/m_voi-stateful-switchover.html), Troubleshooting commands. Checked 2026-09-25. [^14]: show redundancy application if-mgr group shows the VIP interface as no shut on the active router and shut on the standby. Source: [Configure High Availability (HA) on CUBE Routers](https://www.cisco.com/c/en/us/support/docs/unified-communications/unified-border-element/221645-configure-high-availability-ha-on-cube.html), Verify. Checked 2026-09-25. [^15]: The 17.6-onwards configuration guide lists CUBE inbox redundancy as supported only on the ASR 1006 router (disputed). Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - High Availability on Cisco ASR 1000 and Cisco Catalyst 8000 Series Routers](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/m-cube-ha-asr.html), Inbox Redundancy supported platforms. Checked 2026-09-25. [^16]: The CUBE 14 datasheet lists inbox redundancy with both the ASR 1006 and ASR 1006-X (disputed). Source: [Cisco Unified Border Element Version 14 Data Sheet](https://www.cisco.com/c/en/us/products/collateral/unified-communications/unified-border-element/data-sheet-c78-729692.html), High availability row of the features table. Checked 2026-09-25. [^17]: The ASR inbox redundancy example configures redundancy with mode sso and then saves with copy run start. Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - High Availability on Cisco ASR 1000 and Cisco Catalyst 8000 Series Routers](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/m-cube-ha-asr.html), Configuring Inbox Redundancy. Checked 2026-09-25. [^18]: Under CUBE Smart Licensing, inbox high availability requires CUBE Trunk Standard Session licenses. Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - Smart Licensing](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/m_smart_licensing.html), Smart Licensing / Inbox High Availability. Checked 2026-09-25. [^19]: Support for IPv6 flows in CUBE high availability was introduced in Cisco IOS XE Dublin 17.12.1a. Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - High Availability on Cisco 4000 Integrated Services Routers and Cisco Catalyst 8000 Series Edge Platforms](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/m-cube-ha-isr-g3.html), Feature Information table (IPv6 flows in HA). Checked 2026-09-25. [^20]: For CUBE HA as Local Gateway, Cisco recommends the default RG timers (delay 30 and reload 60 seconds) and a holdtime of at least three times the hellotime. Source: [Implement CUBE high availability as Local Gateway](https://help.webex.com/en-us/article/ndiofhf/Implement-CUBE-High-Availability-as-Local-Gateway), Configure redundancy on both CUBEs (timers). Checked 2026-09-25. [^21]: Configuration on both CUBEs of the HA pair must be identical, including physical configuration. Source: [Implement CUBE high availability as Local Gateway](https://help.webex.com/en-us/article/ndiofhf/Implement-CUBE-High-Availability-as-Local-Gateway), Configure redundancy on both CUBEs. Checked 2026-09-25. [^22]: CUBE HA as a Webex Calling Local Gateway requires IOS XE 17.9.1 or later on a platform that supports both CUBE HA and Local Gateway. Source: [Implement CUBE high availability as Local Gateway](https://help.webex.com/en-us/article/ndiofhf/Implement-CUBE-High-Availability-as-Local-Gateway), Prerequisites. Checked 2026-09-25. [^23]: After HA configuration, Local Gateway configuration, whether registration-based or certificate-based, is applied on both HA CUBEs. Source: [Implement CUBE high availability as Local Gateway](https://help.webex.com/en-us/article/ndiofhf/Implement-CUBE-High-Availability-as-Local-Gateway), Configure redundancy on both CUBEs (closing step). Checked 2026-09-25. [^24]: One CUBE of the HA pair must have the lower IP address on all three interfaces compared with the peer's corresponding interfaces. Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - High Availability on Cisco 4000 Integrated Services Routers and Cisco Catalyst 8000 Series Edge Platforms](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/m-cube-ha-isr-g3.html), Restrictions / interface addressing note. Checked 2026-09-25. [^25]: The media inactivity timer lets the HA pair disconnect calls when no RTP is received within a configured period; the example uses timer receive-rtp 1200. Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - High Availability on Cisco 4000 Integrated Services Routers and Cisco Catalyst 8000 Series Edge Platforms](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/m-cube-ha-isr-g3.html), Configuring Media Inactivity Timer. Checked 2026-09-25. [^26]: CUBE high availability is not supported on vCUBE deployed in AWS or Microsoft Azure. Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - Supported Platforms](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/supported-platforms.html), Features Supported. Checked 2026-09-25. [^27]: An ASR 1006 supports both inbox and box-to-box redundancy but cannot switch between the two modes dynamically. Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - High Availability on Cisco ASR 1000 and Cisco Catalyst 8000 Series Routers](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/m-cube-ha-asr.html), Inbox Redundancy. Checked 2026-09-25. [^28]: Media flow-around and the UC Services API are not supported with CUBE box-to-box HA. Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - High Availability on Cisco 4000 Integrated Services Routers and Cisco Catalyst 8000 Series Edge Platforms](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/m-cube-ha-isr-g3.html), Restrictions. Checked 2026-09-25. [^29]: Secondary IP addresses are not permitted on CUBE HA interfaces. Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - High Availability on Cisco 4000 Integrated Services Routers and Cisco Catalyst 8000 Series Edge Platforms](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/m-cube-ha-isr-g3.html), Restrictions. Checked 2026-09-25. [^30]: CUBE HA does not support co-locating Unified SRST or TDM gateway functions on the HA routers. Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - High Availability on Cisco 4000 Integrated Services Routers and Cisco Catalyst 8000 Series Edge Platforms](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/m-cube-ha-isr-g3.html), Restrictions. Checked 2026-09-25. [^31]: WAN links cannot be terminated directly on a CUBE HA router. Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - High Availability on Cisco C8000V Series Cloud Services Routers](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/m-cube-ha-csr.html), Restrictions. Checked 2026-09-25. [^32]: SCCP-based media resources, CPA, noise reduction, acoustic shock protection and transrating calls are not preserved or supported across CUBE HA switchover. Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - High Availability on Cisco 4000 Integrated Services Routers and Cisco Catalyst 8000 Series Edge Platforms](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/m-cube-ha-isr-g3.html), Restrictions. Checked 2026-09-25. [^33]: Out-of-band DTMF using SIP NOTIFY or KPML is not supported on a call after a CUBE HA switchover. Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - High Availability on Cisco 4000 Integrated Services Routers and Cisco Catalyst 8000 Series Edge Platforms](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/m-cube-ha-isr-g3.html), Restrictions. Checked 2026-09-25. [^34]: External devices such as Unified CM must use the CUBE HA Virtual IP address, not the physical interface addresses, as the destination for calls through CUBE. Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - High Availability on Cisco 4000 Integrated Services Routers and Cisco Catalyst 8000 Series Edge Platforms](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/m-cube-ha-isr-g3.html), Redundancy Group Infrastructure (VIP paragraph); final configuration step on pointing external devices to the VIP. Checked 2026-09-25. [^35]: Cisco recommends port channels for the RG control and data interfaces because a single cable or switch path is a single point of failure that can leave both routers Active. Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - High Availability on Cisco 4000 Integrated Services Routers and Cisco Catalyst 8000 Series Edge Platforms](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/m-cube-ha-isr-g3.html), Connection topology recommendations. Checked 2026-09-25. [^36]: Prerequisites for CUBE HA include a Layer 2 connection between the active and standby routers and NTP or identical clocks on both routers. Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - High Availability on Cisco 4000 Integrated Services Routers and Cisco Catalyst 8000 Series Edge Platforms](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/m-cube-ha-isr-g3.html), Prerequisites. Checked 2026-09-25. [^37]: Upon a CUBE HA failover the previously active router reloads by design. Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - High Availability on Cisco 4000 Integrated Services Routers and Cisco Catalyst 8000 Series Edge Platforms](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/m-cube-ha-isr-g3.html), Restrictions. Checked 2026-09-25. [^38]: After completing the CUBE HA configuration the router configuration must be saved and the router reloaded. Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - High Availability on Cisco 4000 Integrated Services Routers and Cisco Catalyst 8000 Series Edge Platforms](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/m-cube-ha-isr-g3.html), Configuring box-to-box redundancy (final reload step). Checked 2026-09-25. [^39]: Any router reloaded while in a CUBE HA relationship always boots up as Standby. Source: [Implement CUBE high availability as Local Gateway](https://help.webex.com/en-us/article/ndiofhf/Implement-CUBE-High-Availability-as-Local-Gateway), Configure redundancy on both CUBEs. Checked 2026-09-25. [^40]: In a CUBE HA pair the control link carries the redundancy state of each router and the data synchronization link carries stateful call and media-flow information. Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - High Availability on Cisco 4000 Integrated Services Routers and Cisco Catalyst 8000 Series Edge Platforms](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/m-cube-ha-isr-g3.html), Redundancy Group Infrastructure. Checked 2026-09-25. [^41]: The RG infra component uses an HSRP-like protocol exchanging keepalive and hello messages to negotiate each router's redundancy state, plus a transport for checkpointing call signaling and media state. Source: [Implement CUBE high availability as Local Gateway](https://help.webex.com/en-us/article/ndiofhf/Implement-CUBE-High-Availability-as-Local-Gateway), Redundancy Group Infra Component. Checked 2026-09-25. [^42]: Cisco recommends connecting the RG control and data interfaces of the pair to the same physical switch to avoid network latency. Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - High Availability on Cisco 4000 Integrated Services Routers and Cisco Catalyst 8000 Series Edge Platforms](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/m-cube-ha-isr-g3.html), Connection topology recommendations. Checked 2026-09-25. [^43]: Adding or removing the redundancy-group command under voice service voip requires a reload to take effect. Source: [Implement CUBE high availability as Local Gateway](https://help.webex.com/en-us/article/ndiofhf/Implement-CUBE-High-Availability-as-Local-Gateway), Configure redundancy on both CUBEs. Checked 2026-09-25. [^44]: Both CUBE HA routers must be in the same data center; geographic stateful switchover and routers connected over MAN Ethernet are not supported. Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - High Availability on Cisco C8000V Series Cloud Services Routers](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/m-cube-ha-csr.html), Restrictions. Checked 2026-09-25. [^45]: CUBE box-to-box HA requires the same redundancy group priority and failover threshold to be configured on both routers. Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - High Availability on Cisco 4000 Integrated Services Routers and Cisco Catalyst 8000 Series Edge Platforms](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/m-cube-ha-isr-g3.html), Restrictions / configuration notes for redundancy group priority. Checked 2026-09-25. [^46]: Both platforms of a box-to-box CUBE HA pair must establish trust with the same CSSM Smart Virtual Account. Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - Smart Licensing](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/m_smart_licensing.html), Smart Licensing / Box-to-Box High Availability. Checked 2026-09-25. [^47]: The CUBE stateful switchover chapter states that calls on hold/resume, transfer and conference are preserved across switchover and that primary and forked call legs are checkpointed. Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - Stateful Switchover Between Redundancy Paired Intra or Inter-box Devices](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/m_voi-stateful-switchover.html), Checkpointing / preserved call flows. Checked 2026-09-25. [^48]: Configuration replicated from the active router lands only in the standby's running configuration and must be committed there with write memory. Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - High Availability on Cisco 4000 Integrated Services Routers and Cisco Catalyst 8000 Series Edge Platforms](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/m-cube-ha-isr-g3.html), Configuration notes on replicating configuration to the standby. Checked 2026-09-25. [^49]: After CUBE HA failover the SIP-layer signaling state is preserved but remote user agents must re-establish TCP sessions before sending further messages. Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - High Availability on Cisco 4000 Integrated Services Routers and Cisco Catalyst 8000 Series Edge Platforms](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/m-cube-ha-isr-g3.html), Restrictions (TCP sessions note). Checked 2026-09-25. [^50]: TAC tech note 221645 demonstrates CUBE HA on ASR1001-X routers running IOS XE 16.09.04. Source: [Configure High Availability (HA) on CUBE Routers](https://www.cisco.com/c/en/us/support/docs/unified-communications/unified-border-element/221645-configure-high-availability-ha-on-cube.html), Components Used. Checked 2026-09-25. [^51]: Interface tracking of the LAN and WAN interfaces (for example track 1 interface ... line-protocol) is assigned to the redundancy group so that traffic-interface failure triggers switchover. Source: [Configure High Availability (HA) on CUBE Routers](https://www.cisco.com/c/en/us/support/docs/unified-communications/unified-border-element/221645-configure-high-availability-ha-on-cube.html), Configure / interface tracking and assign tracks to redundancy group. Checked 2026-09-25. [^52]: Calls still in transit, for example in trying or ringing state, are not checkpointed by CUBE HA. Source: [Implement CUBE high availability as Local Gateway](https://help.webex.com/en-us/article/ndiofhf/Implement-CUBE-High-Availability-as-Local-Gateway), Layer 2 Box-to-Box Redundancy. Checked 2026-09-25. [^53]: TCP, TLS and UDP transport-layer sessions are not checkpointed between the CUBE HA pair. Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - High Availability on Cisco 4000 Integrated Services Routers and Cisco Catalyst 8000 Series Edge Platforms](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/m-cube-ha-isr-g3.html), Restrictions. Checked 2026-09-25. [^54]: Up to two active/standby CUBE HA pairs (two redundancy groups) may exist in the same Layer 2 segment, with a unique RII per redundant interface pair. Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - High Availability on Cisco 4000 Integrated Services Routers and Cisco Catalyst 8000 Series Edge Platforms](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/m-cube-ha-isr-g3.html), Redundancy Interface Identifier note. Checked 2026-09-25. [^55]: VIPs are assigned on each redundant interface with the form redundancy group ip
exclusive. Source: [Configure High Availability (HA) on CUBE Routers](https://www.cisco.com/c/en/us/support/docs/unified-communications/unified-border-element/221645-configure-high-availability-ha-on-cube.html), Configure / Virtual IPs on LAN and WAN side. Checked 2026-09-25. [^56]: All CUBE HA signaling and media is sourced from and sent to the Virtual IP address configured on the externally facing interfaces. Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - High Availability on Cisco 4000 Integrated Services Routers and Cisco Catalyst 8000 Series Edge Platforms](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/m-cube-ha-isr-g3.html), Redundancy Group Infrastructure / Virtual IP Address. Checked 2026-09-25. [^57]: VRFs must be defined identically and in the same order on both active and standby routers for accurate data synchronisation. Source: [Cisco Unified Border Element Configuration Guide - Cisco IOS XE 17.6 Onwards - High Availability on Cisco 4000 Integrated Services Routers and Cisco Catalyst 8000 Series Edge Platforms](https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/voice/cube/ios-xe/config/ios-xe-book/m-cube-ha-isr-g3.html), VRF configuration notes. Checked 2026-09-25. [^58]: Webex Contact Center component-redundancy guidance requires CUBE HA peers to use the same hardware, the same software configuration and the same IOS version, with VIPs for signaling and media. Source: [Component Redundancy](https://help.webex.com/article/yr5u2m), CUBE Redundancy Within the Enterprise Network. Checked 2026-09-25.