High-Availability (HA) technologies - NSR (GR)

BGP Nonstop Routing


BGP NSR is a unique, self-contained routing high-availability solution that extends IP high-availability deployments and benefits to the entire
edge. Currently BGP supports NSF (through BGP Graceful Restart) as part of the NSF/SSO high-availability offering in Cisco IOS Software.
BGP NSR extends the routing high-availability capabilities to the next level by “maintaining all necessary” BGP routing and session
information across a route-processor switchover.

Cisco support for BGP Nonstop Forwarding (also called Graceful Restart) follows the implementation specification described in the IETF proposed standard. According to this implementation, to achieve continuous packet forwarding the following conditions must be met:

• The NSF-capable router and the peer router must each agree to support BGP Graceful Restart.

• The peer router must not prematurely declare the NSF-capable router as unavailable.

• The peer router must not communicate any state change in the NSF-capable router to any of its peers. This avoids the networkwide detrimental effect on performance associated with the sudden failure of a router.

• The peer router must send BGP updates to help the restarting NSF-capable router to reacquire its BGP RIB.

• The peer router must signal the completion of the initial routing update by sending the End-of-RIB marker.

• In the interim (before the restarting NSF-capable router has reacquired the routing information), the peer router must mark any routes associated with the restarting router as "stale", but continue to use those routes for packet forwarding.


From:Cisco IOS Software High-Availability Enhancements for IP/MPLS Provider Edge
Cisco Nonstop Forwarding with Stateful Switchover Deployment Guide

HIGH AVAILABILITY (HA) technologies - Cisco NSF

Cisco NSF and Timer Manipulation for Fast Convergence

Cisco NSF with SSO is a Cisco innovation for systems with dual route processors. Cisco NSF with SSO allows a router that has experienced a hardware or software failure of an active route processor to maintain data link layer connections and to continue forwarding packets during the switchover to the standby route processor. This forwarding can continue despite the loss of routing protocol peering arrangements with other routers. Routing information is recovered dynamically in the background, while packet forwarding proceeds uninterrupted.

Initially, it appears that Cisco NSF and OSPF/ISIS/EIGRP timer manipulation have complimentary objectives. Each feature is dedicated to achieving the fastest possible convergence in the event of a failure on a router. However, more careful analysis reveals that these technologies also have conflicting goals. Cisco NSF attempts to maintain the flow of traffic through a router that has experienced a failure; conversely, OSPF/ISIS/EIGRP timer manipulation tries to quickly redirect the flow of traffic away from a router that has experienced a failure towards an alternate path. While not mutually exclusive, the two technologies try to address different aspects of the same problem in disparate ways. It is therefore important to carefully consider the network design goals and establish precedence for redundancy.

The network designer has three alternatives

1. Raise the IGP hold-timers to seven seconds to accommodate all failure scenarios. Setting the timer to this value would account for the situation in which the route processor has to be detected via IPC keep-alive failure (3 seconds) plus the safe value for post-switchover behavior (4 seconds for the Cisco 10000 and 12000 Series Internet Routers).

2. Leave the IGP hold-timers at 4 seconds. This will allow Cisco NSF with SSO to operate as expected in the majority of failure scenarios. In the exception cases, where the route processor needs to use IPC keep-alive to determine the need to switchover to the redundant route processor, the traffic will failover to a redundant path on a different system. Remember, the keep-alive procedure is a "failsafe" mechanism while the internal switchover signaling procedures are expected to cover most failures.

3. Lower the IPC keep-alive timer. This can be achieved with the command "redundancy/main-cpu/switchover timeout <milliseconds>". By default, this timer is set for 3 seconds, and can be lowered with the preceding command. It should be strongly emphasized that there is an element of risk to lowering this timer. If the standby route processor does not hear from the active route processor within the timeout period, an route processor switchover will be initiated. Thus, if this timer is set to a very low value, there is the danger of false alarms-causing an route processor switchover when one is not required. In addition, there will be increased CPU and IPC bandwidth usage associated with setting this timer to a very low value.

From:Cisco NSF and Timer Manipulation for Fast Convergence

Tuning for input and output drops

SPD and Input-queue tuning for input drops and flushes
http://www.cisco.com/en/US/products/hw/routers/ps167/products_tech_note09186a008012fb87.shtml
http://www.cisco.com/web/about/security/intelligence/spd.html

Queue-limit tuning for output drops

http://www.cisco.com/en/US/products/hw/routers/ps341/products_tech_note09186a0080af893d.shtml
http://www.cisco.com/en/US/docs/ios/12_0s/feature/guide/12simql.html

service compress-config

Usage Guidelines

After you configure the service compress-config command, the router will compress configuration files every time you save a configuration to the startup configuration. For example, when you enter the copy system:running-config nvram:startup-config command, the running configuration will be compressed before storage in NVRAM. 

Ref:Configuration File Management Commands 

http://www.davidsudjiman.info/2008/10/20/service-compress-config/ 

Configuration Generation Performance Enhancement

The Configuration Generation Performance Enhancement feature assists configuration management by enabling faster collection of running configuration file information. This feature is especially useful in managing large networks with numerous interfaces configured. 

Cisco IOS Software Configuration Storage

In the Cisco IOS software configuration model, the configuration state is maintained in a distributed manner, with each component storing its own configuration state. To retrieve configuration information, the software must poll every component to collect the distributed information. This configuration state retrieval operation is performed by a process known as nonvolatile generation (NVGEN), and it is used by command-line interface (CLI) commands such as show running-config, write memory, and copy system:running-configuration to display or copy the running system configuration. When invoked, NVGEN queries each system component and each instance of interface or other configuration objects. A running configuration file is constructed as NVGEN traverses the system performing these queries.  

Note If you try to configure the write memory command when a router is low on memory and the backup buffer cannot be allocated, then the command will fail with the error message, "Not enough space." When the write memory command fails to apply the new configuration, the backup configuration is used to restore the original configuration.  

Benefits of the Configuration Generation Performance Enhancement

Before the Configuration Generation Performance Enhancement feature was introduced, NVGEN always had to query the entire system and could generate only a total configuration. The time required to process the running configuration creates performance problems for configuration management, because completion of the NVGEN operation can take many minutes.

The Configuration Generation Performance Enhancement feature reduces the execution time for NVGEN processes and is especially useful for managing large configuration files that contain numerous interface configurations. This feature provides faster execution of commands that process the running system configuration by caching interface configuration information in system memory, and by retrieving only configuration information that has changed.

Configuring the Configuration Generation Performance Enhancement

Perform this task to enable the Configuration Generation Performance Enhancement.

SUMMARY STEPS

1. enable

2. configure terminal

3. parser config cache interface

4. end

Ref: http://www.cisco.com/en/US/partner/docs/ios/fundamentals/configuration/guide/config_cache_ps6922_TSD_Products_Configuration_Guide_Chapter.html

IPERF traffic direction

IPERF

Normally, the iperf client will send traffic to the server.

e.g. in UDP mode, the client will send almost 100% traffic to server side.

In TCP mode, the client will send two times of traffic than other way around.

The show processes Command

router#show processes 
CPU utilization for five seconds: 0%/0%; one minute: 0%; five minutes: 0%

CPU utilization for the last five seconds. 

The second number indicates the percent of CPU time spent at the interrupt level.

The show processes Command