Table Of Contents

High Availability Overview

Hardware Redundancy Overview on the Cisco ASR 1000 Series Routers

Software Redundancy on the Cisco ASR 1000 Series Routers

Software Redundancy Overview

Second IOS Process on a Cisco ASR 1002 or 1004 Router

Route Processor Redundancy

Stateful Switchover

SSO-Aware Protocol and Applications

Bidirectional Forwarding Detection

High Availability Overview

---

Cisco High Availability (HA) enables network-wide protection by providing fast recovery from faults that may occur in any part of the network. With Cisco High Availability, network hardware and software work together and enable rapid recovery from disruptions to ensure fault transparency to users and network applications.

The unique hardware and software architecture of the Cisco ASR 1000 Series Routers is designed to maximize router uptime during any network event, and thereby provide maximum uptime and resilience within any network scenario.

This chapter covers the aspects of High Availability that are unique to the Cisco ASR 1000 Series Routers. It is not intended as a comprehensive guide to High Availability, nor is it intended to provide information on High Availability features that are available on other Cisco routers that are configured and implemented identically on the Cisco ASR 1000 Series Routers. The Cisco IOS feature documents and guides should be used in conjunction with this chapter to gather information about High Availability-related features that are available on multiple Cisco platforms and work identically on the Cisco ASR 1000 Series Routers.

This section discusses various aspects of High Availability on the Cisco ASR 1000 Series Routers and contains the following sections:

•Hardware Redundancy Overview on the Cisco ASR 1000 Series Routers

•Software Redundancy on the Cisco ASR 1000 Series Routers

•Route Processor Redundancy

•Stateful Switchover

•Bidirectional Forwarding Detection

Hardware Redundancy Overview on the Cisco ASR 1000 Series Routers

Some models of the Cisco ASR 1000 Series Routers offer hardware redundancy within the same Cisco ASR 1000 Series Router through the following methods:

•Allowing two Route Processors (RPs) in the same Cisco ASR 1000 Series Router

•Allowing two Enhanced Services Processors (ESPs) in the same Cisco ASR 1000 Series Router

No hardware redundancy is supported for the following hardware:

•SPA interface processors (SIPs)—A SIP must be reloaded, and traffic briefly interrupted, for a SIP upgrade to complete.

•Shared port adapters (SPAs)—A SPA must be reloaded, which will briefly interrupt traffic to that SPA, for a SPA software sub-package update to complete.

Hardware redundancy on the Cisco ASR 1000 Series Routers gives users the following benefits:

•A failover option—If a processor fails, the standby processor immediately becomes the active processor with little or no delay. The failover happens completely within the same router, so a second standby router is not needed.

•No downtime upgrades—Using features like ISSU, a software upgrade can be handled on the standby processor while the active processor continues normal operation.

Hardware redundancy is available on the Cisco ASR 1006 Router only at this time.

Table 6-1 provides a hardware redundancy overview.

Table 6-1

Hardware	Support for Dual Hardware Configuration on Cisco ASR 1002 Router	Support for Dual Hardware Configuration on Cisco ASR 1004 Router	Support for Dual Hardware Configuration on Cisco ASR 1006 Router	Failover Behavior
Enhanced Services Processor	No	No	Yes	If an active ESP experiences a hardware or software event that makes it unable to forward traffic (such as a hardware failure, an OIR, or a manual switch) and a standby ESP is configured, the standby ESP becomes the active ESP with the possibility of a minor interruption (less than 200 ms).
Route Processor	No	No	Yes	If an active RP experiences an event that makes it unable to forward traffic (such as a hardware failure, a software failure, an OIR, or a manual switch) and a standby RP is configured, the standby RP immediately becomes the active RP.
SPA	No	No	No	No standby configurations are available for SPAs. If a SPA fails, that particular SPA is down and unable to forward traffic. In the event of a SPA shutdown, all other SIPs and SPAs on the router continue to be fully operational.
SIP	No	No	No	No standby configurations are available for SIPs. If a SIP fails, all SPAs in that SIP are down and unable to forward traffic. In the event of a SIP shutdown, all other SIPs and SPAs on the router continue to be fully operational.

Hardware Redundancy Overview

Software Redundancy on the Cisco ASR 1000 Series Routers

This section covers the following topics:

•Software Redundancy Overview

•Second IOS Process on a Cisco ASR 1002 or 1004 Router

•SSO-Aware Protocol and Applications

Software Redundancy Overview

On the Cisco ASR 1000 Series Routers, IOS runs as one of many processes within the operating system. This is different than on traditional Cisco IOS, where all processes are run within Cisco IOS. See the "IOS as a Process" section on page 2-7 for more information regarding IOS as a process on the Cisco ASR 1000 Series Router.

This architecture allows for software redundancy opportunities that are not available on other platforms that run Cisco IOS software. Specifically, a standby IOS process can be available on the same Route Processor as the active IOS process. This standby IOS process can be switched to in the event of an IOS failure, and can also be used to upgrade sub-package software in some scenarios as the standby IOS process in an ISSU upgrade.

On the Cisco ASR 1006 Router, the second IOS process can run only on the standby Route Processor. Two IOS processes on the same Router Processor are not possible for any Cisco ASR 1000 Series Router that supports dual RP hardware redundancy configurations since the second Route Processor can support a standby IOS process. An overview of software redundancy is shown in Table 6-2.

Table 6-2 Software Redundancy Overview

Router	Support for Two IOS Processes on Same Route Processor	Support for a Second IOS Process on Standby Route Processor	Explanation
Cisco ASR 1002 Router	Yes	N/A	The Cisco ASR 1002 Router only supports one RP, so dual IOS processes run on the lone RP.
Cisco ASR 1004 Router	Yes	N/A	The Cisco ASR 1004 Router only supports one RP, so dual IOS processes run on the lone RP.
Cisco ASR 1006 Router	No	Yes	The Cisco ASR 1006 Router supports a second Route Processor, so the second IOS process can only run on the standby Route Processor.

Second IOS Process on a Cisco ASR 1002 or 1004 Router

For Cisco ASR 1002 and 1004 routers, Route Processor Redundancy and Stateful Switchover can be used to switch between IOS processes. RPR and SSO need to be configured by the user, however, because a second IOS process is not available by default on Cisco ASR 1002 and 1004 routers.

Table 6-3 summarizes the software redundancy opportunities available with the second IOS process for the Cisco ASR 1002 and 1004 routers.

Table 6-3

Router	Default HA Setting	Options on Router with 2 GB or DRAM	Options with 4 GB or DRAM
Cisco ASR 1002 Router	None	None	None, RPR, SSO
Cisco ASR 1004 Router	None	None	None, RPR, SSO

Software Redundancy Options for Cisco ASR 1002 and 1004 Routers

ISSU cannot be used to upgrade consolidated packages on Cisco ASR 1002 or 1004 Routers, and only a few sub-packages can be upgraded individually using ISSU through the use of dual IOS processes on the same Route Processor. See the "Route Processor Redundancy" section for more information on which sub-packages can be upgraded using ISSU in a dual RP setup.

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).

On the Cisco ASR 1000 Series Router, RPR can also be used to enable a second IOS process on a single RP for a Cisco ASR 1002 or 1004 Router. See the "Second IOS Process on a Cisco ASR 1002 or 1004 Router" section for additional information on the second IOS process.

For the Cisco ASR 1000 Series Routers, RPR introduces the following functionality:

•Startup configuration synchronization between the active and standby RP or IOS process. It is important to note, however, that changes in the running configuration are not synchronized using RPR.

•Warm Reload—The Warm Reload feature allows users to reload their routers without reading images from storage; that is, the router reboots by restoring the read-write data from a previously saved copy in the RAM and by starting execution without either copying the software from flash to RAM or self-decompression of the image.

It is important to note that in most cases, Stateful Swithover (SSO) requires less downtime for switchover and upgrades than RPR. RPR should only be used when there is a compelling reason to not use SSO.

It is important to note RPR is supported on the Cisco ASR 1000 Series Routers while RPR+ is not.

Stateful Switchover

The Stateful Switchover (SSO) feature takes advantage of processor redundancy by establishing one of the processors as the active processor while the other RP is designated as the standby processor, and then synchronizing critical state information between them. Following an initial synchronization between the two processors, SSO dynamically maintains RP state information between the dual processors.

Stateful Switchover is particularly useful in conjunction with Nonstop Forwarding. SSO allows the dual processors to maintain state at all times, and Nonstop Forwarding lets a switchover happen seamlessly when a switchover occurs.

On the Cisco ASR 1000 Series Router, SSO can also be used to enable a second IOS process on a single RP for a Cisco ASR 1002 or 1004 Router. See the "Second IOS Process on a Cisco ASR 1002 or 1004 Router" section for additional information on the second IOS process.

It is important to note that in most cases, SSO requires less downtime for switchover and upgrades than RPR. RPR should only be used when there is a compelling reason to not use SSO.

For additional information on NSF/SSO, see the Cisco Nonstop Forwarding document.

SSO-Aware Protocol and Applications

SSO-supported line protocols and applications must be SSO-aware. A feature or protocol is SSO-aware if it maintains, either partially or completely, undisturbed operation through an RP switchover. State information for SSO-aware protocols and applications is synchronized from active to standby to achieve stateful switchover for those protocols and applications.

The dynamically created state of SSO-unaware protocols and applications is lost on switchover and must be reinitialized and restarted on switchover.

To see which protocols are SSO-aware on your router, enter the show redundancy comp-matrix command.

Bidirectional Forwarding Detection

Bidirectional Forwarding Detection (BFD) is a detection protocol designed to provide fast forwarding path failure detection times for all media types, encapsulations, topologies, and routing protocols. In addition to fast forwarding path failure detection, BFD provides a consistent failure detection method for network administrators. Because the network administrator can use BFD to detect forwarding path failures at a uniform rate rather than the variable rates for different routing protocol hello mechanisms, network profiling and planning is easier, and reconvergence time is consistent and predictable.

For more information on BFD, see the Bidirectional Forwarding Detection document.

For the Cisco ASR 1000 Series Routers, BFD for IPv4 Static Routes and BFD for BGP are supported.