High Availability (HA) is a feature that ensures the availability of resources in a computer system, in case of component failures in the system. The unique hardware and software architecture of the Cisco ASR1000 Series, Cisco ISR G2 and Cisco ISR 4000 Series routers is designed to maximize router uptime during any network event, and thereby provide maximum uptime and resilience within any network scenario. Figure 1: CUBE High Availability The diagram above illustrates the CUBE's HA feature that allows active calls to be preserved when a CUBE router experiences an outage. This chapter provides a brief overview of the different types of high availability (HA) options on the Cisco routers for the CUBE Enterprise edition. Information About High Availability, page 1 Restrictions for CUBE High Availability, page 5 Information About High Availability Inbox versus Box-to-Box Redundancy Refer to the next section in this document. For detailed information about inbox and box-to-box redundancies, refer to the chapter titled Stateful Switchover Between Redundancy Paired Intra- or Inter-box Devices in the. 1
Route Processor Redundancy Route Processor Redundancy Route Processor Redundancy (RPR) allows you to configure a standby RP. When you configure RPR, the standby RP loads the Cisco IOS software on bootup and initializes itself in standby mode. In the event of a fatal error on the active RP, the system switches to the standby RP, which reinitializes itself as the active RP. In this event, the entire system is rebooted, so the switchover with RPR is slower than with other High Availability switchover features such as Nonstop Forwarding/Stateful Switchover (NSF/SSO). Stateful Switchover Stateful switchover (SSO) provides media preservation of calls and post-switchover teardown of calls, in case of active RP failure. This means that the CUBE calls would continue to be active even after the active RP card goes down (provided a redundant RP is present). The standby RP would become active and service new CUBE(ENT) calls. The context of the CUBE (ENT) calls that were switched over from the Active card would be present on the new active card. Hold/Resume or any other supplementary services will work after switchover. In SSO, both media and signaling session context are preserved on failover. Note The terms failover and switchover are used interchangeably. Nonstop Forwarding Nonstop forwarding (NSF) helps to suppress routing flaps in devices that are enabled with stateful switchover (SSO), thereby reducing network instability. NSF allows for the forwarding of data packets to continue along known routes while the routing protocol information is being restored after a switchover. Non Stop Forwarding (NSF) works together with SSO and allows the routing protocols to reestablish their routing information by requesting their network neighbors to resend all of the routing information when a switchover occurs. HA Checkpointing Checkpointing refers to the facility or architecture to implement stateful switchover (SSO). It provides the mechanisms to help synchronize state data between the active and standby route processors or chassis in a consistent, repeatable, and well-ordered manner. From Cisco IOS Release 15.6(1)T and Cisco IOS-XE Release 3.17S onwards, checkpointing mechanism is enhanced to provide support for multimedia endpoints with larger SDP up to 6000 bytes. With the new enhancement, CUBE supports preservation of media up to a maximum of 6 m-lines/streams (audio, video, and application). CUBE HA is enhanced to support the preservation of Record-Route and Contact header information. After SSO, all subsequent midcall SIP messages will be routed based on the correct Record-Route and Contact headers. 2
CUBE High Availability Options CUBE High Availability Options The CUBE HA implementation supports full stateful failover for active SIP-to-SIP calls. This means both media and signaling session information is preserved after switchover. The Cisco Unified Border Element (CUBE) provides three types of high availability (HA) options: Inbox redundancy Supported only on ASR devices. Inbox redundancy with Stateful Switchover (SSO) mechanism provides redundancy within the same device. Some models of the ASR offer hardware redundancy within the box and some offer software redundancy. Hardware redundancy Supports stateful failover from an active Enhanced Services Processor to a standby and from an active route processor to a standby on the same box. Cisco ASR1006 supports this type of failover. Software redundancy Supports stateful failover from an active IOS process to a standby process, both running on the same route processor. This is different than the platforms running Cisco IOS such as the ISR G2 devices, where only one process can run on the operating system. Cisco ASR1001/1002/1004 supports this type of failover. Figure 2: Inbox Redundancy L2 box-to-box redundancy (stateful failover of active calls) ASR, ISR G2, and ISR G3 platforms support box-to-box HA. The redundancy protocols used are: ASR Redundancy Group (RG) infrastructure ISR G2 Hot Standby Routing Protocol (HSRP) ISR G3 Redundancy Group (RG) infrastructure Figure 3: L2 Box-to-Box Redundancy 3
CUBE High Availability Options Clustering with load balancing Clustering is supported on ISR G2 and ASR devices. Clustering with load balancing provides local and geographical redundancies. Load balancing can be achieved using Cisco Unified SIP Proxy (CUSP) or using a Service Provider (SP) call agent. Figure 4: Clustering with Load Balancing Hot Standby Routing Protocol (ISR-G2 Devices) The Cisco Unified Border Element (CUBE) provides high availability (HA) using box-to-box redundancy configurations when implemented on a Cisco ISR-G2 platform. CUBE box-to-box redundancy on ISR-G2 is based on the Hot Standby Routing Protocol (HSRP) router technology, and HSRP is specific to ISR-G2. HSRP technology provides high network availability by routing IP traffic from hosts on networks without relying on the availability of any single router. HSRP is used in a group of routers for selecting an Active router and a Standby router. HSRP monitors both the inside and outside interfaces if any interface goes down, the whole device is considered down, the standby device becomes active and takes over the responsibilities of the active router. Box-to-box high availability is supported using virtual IP addresses for the signaling and media. For more information about HA support using virtual IP addresses, refer to the section titled Stateful Switchover Between Redundancy Paired Intra- or Inter-box Devices in the CUBE Configuration Guide. RG Infrastructure (ASR Devices) On the ASR, box-to-box redundancy option (introduced in the previous section) uses the Redundancy Group (RG) Infrastructure to form an Active/Standby pair of routers. The Active/Standby pair share the same virtual IP address (VIP) and continually exchange status messages. CUBE session information is check-pointed across the Active/Standby pair of routers enabling the Standby router to take over immediately all CUBE call processing responsibilities if the Active router should go out of service. This redundancy option is supported on the ASR 1001/1002-X/1004 platforms, and with Cisco IOS XE 3.11S, it is also supported on ASR 1006 with a single route processor and an Embedded Services Processor (ESP). ASR 1006 supports both box-to-box and inbox redundancy, and you cannot switch between these two modes dynamically. Box-to-box redundancy requires two identical ASR platforms on the same physical LAN. Redundancy Group (RG) Infra component provides the box-to-box communication infrastructure support between the two ASRs and will negotiate the final stable redundancy state. The RG Infra component provides: An HSRP-like protocol that negotiates the final redundancy state for each router by exchanging keepalive and hello messages between the two ASRs in pair (using the control interface). A transport mechanism for checkpointing the signaling and media state for each call from the ACTIVE to the STANDBY router (using the data interface). Configuration/management of the virtual IP (VIP) interface for the traffic interfaces (multiple traffic interfaces can be configured using the same RG). 4
Considerations for Choosing an HA Configuration Note Licensing implications and configuration details are not covered in this chapter. For information about HA, refer to the High Availability section in the CUBE Advanced guide. Considerations for Choosing an HA Configuration When considering HA design, the following VoIP aspects apply: Media preservation of active calls Calls that are currently being signaled Signaling protocol state preservation for active calls (supplementary services will work after switchover) Transcoded calls Calls using software MTP on the CUBE H323-to-SIP and H323-to-H323 calls Licensing implications Restrictions for CUBE High Availability IPv6 is not supported on CUBE HA. 5
Restrictions for CUBE High Availability 6