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Table Of Contents
Router-Shelf Redundancy for the Cisco AS5800
Related Features and Technologies
Configuring the Cisco AS5800 for Shelf Redundancy
Configuring the Shelf Redundancy Feature
Feature Information for Router-Shelf Redundancy for the Cisco AS5800
Router-Shelf Redundancy for the Cisco AS5800
This document describes router-shelf redundancy for the Cisco AS5800 universal access server. It includes the following sections:
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Feature Information for Router-Shelf Redundancy for the Cisco AS5800
Feature Overview
This feature provides router-shelf redundancy by using a second router shelf that automatically takes over the other shelf's dial-shelf cards (DSCs) if it appears that the other router shelf has died. Failover is disruptive in that there is no attempt to maintain calls that were established on the failing router shelf; the DSCs controlled by the failing router shelf are restarted under control of the backup router shelf and hence become available again.
Two router shelves are connected to the same DSC (as in split mode), but with only one router shelf active at a time. Both router shelves are configured for normal mode as opposed to split mode. Each router shelf contains the same configuration, being whatever configuration is appropriate for the full set of DSCs. The active router shelf controls all the DSCs, while the other router shelf functions purely as a backup. If the active router shelf fails, all DSCs restart under the control of the backup router shelf, which then functions as the active router shelf.
Only one router shelf has control of the DSCs at a time; the other keeps trying to take control but is unable to, and does not interfere with operation of the active router shelf. If, however, the active router shelf crashes, then it relinquishes control of all DSCs to the other router shelf, which restarts the DSCs and commences normal operation. If the crashed router shelf recovers or is restarted, it does not take back control of the DSCs, but instead functions as a backup, and takes control again only if the other router shelf fails.
External interfaces cannot share the same IP address between the two routers shelves, to prevent duplicate IP address errors.
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Additional Considerations
System Controller
When a system controller is used with a redundant router shelf, router-shelf failover should look like a single router shelf going down briefly and then recovering. With the current system-controller code, this does not work. The Cisco SC3640 expects only a single router shelf to be configured with any given shelf ID. To get around this, a router in backup mode must be prevented from sending Session Definition Protocol (SDP) packets to the Cisco SC3640. In addition, the SDP packets sent by the router shelves to the Cisco SC3640 currently include a field identifying the MAC address of the sending router. The Cisco SC3640 stores this MAC address and, if it subsequently receives another SDP packet containing the same shelf ID but not the same MAC address, it concludes that multiple routers are configured with the same shelf ID and treats this as an error. This is precisely the situation after a failover, when the backup router shelf starts sending SDP packets with the same shelf ID but different MAC address.
To get around this, you must configure a failover group code—an integer that identifies a redundant pair of router shelves. Each member of the pair must be configured with the same group code. When failover mode is enabled, this group code is sent in place of the router MAC address. These changes are all made to the system-controller code that runs on the router shelf itself, rather than on the Cisco SC3640.
Load Sharing
There is no load sharing between the two routers shelves—no calls can go through the backup router shelf. One disadvantage of this is that you cannot split the load between the routers to reduce the number of calls that are lost when a router crashes. There are, however, also some advantages: with load sharing, you must ensure that each router can support the entire dial shelf, since upon failure of a router shelf the surviving router shelf owns all the dial-shelf resources, and therefore has a sudden change in the amount of traffic it is supporting. If care had not been taken to test under failover conditions, at full load the surviving router shelf might be overwhelmed, and perhaps provide degraded service. With a redundant router shelf instead acting purely as a standby, provided that the backup router shelf is the same model as the active router shelf, the load is unchanged after switchover—so no change is expected to the router-shelf performance.
Having a single router shelf active at a time is simpler, and makes it easier to support failover when dealing with external servers such as signaling controllers for SS7, RPMS server, and system controllers.
Hitless Redundancy
When router-shelf failover occurs, all calls associated with the failed router shelf are lost. To maintain calls through router-shelf failure requires mirroring call state and fast failure detection. This shelf-redundancy feature ensures only that resources (particularly trunk lines) do not remain unusable while the router shelf that was controlling them is down.
Network Management
Minimal Simple Network Management Protocol (SNMP) support is provided—a trap is issued when failover occurs, and SNMP variables indicate whether a router shelf is active or on standby. An existing MIB—CISCO-C8500-REDUNDANCY-MIB—defines a suitable trap for issuing on failover.
Benefits
When an active router shelf in a Cisco AS5800 loses communication with its DSC, a backup router shelf can be invoked to automatically take over DSCs controlled by the lost router shelf. This backup method, called redundancy, is provided on the Cisco AS5800 to prevent a single point of failure, subsequent downtime, and user intervention to resolve unrecoverable hardware faults.
Restrictions
Router Shelves
Two router shelves of the same model and configuration must be available for this feature to operate.
External Servers
Although some of the failover functionality exists in the existing code base, ensure that the various external servers that can run with the Cisco AS5800 still function when redundant router shelves are used. The servers of concern at the moment are RPMS, SS7, and System Controller; the first two are discussed below:
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Related Features and Technologies
RSC Handover Redundancy
The Router Shelf Controller Handover Redundancy feature that is available on the Cisco AS5850 is similar to Router Shelf Redundancy on the Cisco AS5800.
Prerequisites
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Configuration Examples
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Configuring the Cisco AS5800 for Shelf Redundancy
Connect to each router shelf in turn and enter these commands. Treat router shelves as if they are connected as a split dial-shelf configuration.
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Configuring the Shelf Redundancy Feature
Verifying Shelf Redundancy
Use the show redundancy command to verify whether the "Shelf is redundant" string is displayed on a redundancy-enabled access server, as illustrated below:
Router# show redundancyT1 1/0 is up.Applique type is Channelized T1Cablelength is long gain36 0dbNo alarms detected.alarm-trigger is not setVersion info of slot 3: HW: 256, PLD Rev: 1Framer Version: 0x8Manufacture Cookie Info:EEPROM Type 0x0001, EEPROM Version 0x01, Board ID 0x02,Board Hardware Version 1.0, Item Number 32-0-00,Board Revision 00, Serial Number 12059498,PLD/ISP Version <unset>, Manufacture Date 19-Jun-1999.Framing is ESF, Line Code is AMI, Clock Source is Line.Trunk setting is rbs-zero.Data in current interval (619 seconds elapsed):380 Line Code Violations, 171 Path Code Violations0 Slip Secs, 0 Fr Loss Secs, 137 Line Err Secs, 10 Degraded Mins137 Errored Secs, 21 Bursty Err Secs, 0 Severely Err Secs, 0 Unavail SecsTotal Data (last 24 hours)203903 Line Code Violations, 27284 Path Code Violations,7 Slip Secs, 531 Fr Loss Secs, 18414 Line Err Secs, 1431 Degraded MinsThe following example shows output from two router shelves configured as a failover pair. The active router shelf is initially RouterA. The commands show redundancy history and show redundancy have been issued. The show redundancy command shows that failover is enabled and shows the configured group number. The show redundancy command also shows that this router shelf is the active one of the pair. Compare this output with that from the backup router shelf (RouterB) further below.
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Log from the First Router Shelf (RouterA):
RouterA#RouterA# show redundancy historyDSC Redundancy Status Change History:010215 18:17 Slot -1 DSC:Failover configured -> ACTIVE role by default.010215 18:18 Slot -1 DSC:Failover -> BACKUP role.010215 18:18 Slot 12 DSC:Failover -> ACTIVE role.010215 18:18 Slot 12 DSC:Hub, becoming active - arb timeoutRouterA#RouterA# show redundancyfailover mode enabled, failover group = 32Currently ACTIVE role.DSC in slot 12:Hub is in 'active' state.Clock is in 'active' state.No connection to slot 13RouterA#RouterA# reloadProceed with reload? [confirm]*Feb 15 20:19:11.059:%SYS-5-RELOAD:Reload requestedSystem Bootstrap, Version 11.1(13)CA, EARLY DEPLOYMENT RELEASE SOFTWARE (fc1)Copyright (c) 1997 by cisco Systems, Inc.C7200 processor with 131072 Kbytes of main memoryrommon 1 >Log from the Second Router Shelf (RouterB):
RouterB#RouterB# show redundancyfailover mode enabled, failover group = 32Currently BACKUP role.No connection to slot 12DSC in slot 13:Hub is in 'backup' state.Clock is in 'backup' state.RouterB#*Feb 16 03:24:53.931:%DSC_REDUNDANCY-3-BICLINK:Switching to DSC 13*Feb 16 03:24:53.931:%DSC_REDUNDANCY-3-BICLINK:Failover:changing to active mode*Feb 16 03:24:54.931:%DIAL13-3-MSG:02:32:06:%DSC_REDUNDANCY-3-EVENT:Redundancy event:LINK_FAIL from other DSC*Feb 16 03:24:55.491:%OIR-6-INSCARD:Card inserted in slot 12, interfaces administratively shut down*Feb 16 03:24:58.455:%DIAL13-3-MSG:02:32:09:%DSC_REDUNDANCY-3-EVENT:Redundancy event:LINK_FAIL from other DSC*Feb 16 03:25:04.939:%DIAL13-0-MSG:RouterB# show redundancyfailover mode enabled, failover group = 32Currently ACTIVE role.No connection to slot 12DSC in slot 13:Hub is in 'active' state.Clock is in 'backup' state.RouterB# show redundancy historyDSC Redundancy Status Change History:010216 03:09 Slot -1 DSC:Failover configured -> BACKUP role.010216 03:24 Slot 13 DSC:Failover -> ACTIVE role.010216 03:24 Slot 13 DSC:Hub, becoming active - D12 linkfail010216 03:24 Slot 13 DSC:Hub, becoming active - D12 linkfailRouterB#*Feb 16 03:26:14.079:%DSIPPF-5-DS_HELLO:DSIP Hello from shelf 47 slot 1 Succeeded*Feb 16 03:26:14.255:%DSIPPF-5-DS_HELLO:DSIP Hello from shelf 47 slot 3 Succeeded*Feb 16 03:26:14.979:%DSIPPF-5-DS_HELLO:DSIP Hello from shelf 47 slot 10 SucceededAdditional References
Related Documents
Cisco IOS commands
AS5800 Operations, Administration, Maintenance, and Provisioning (OAM&P) Guide
http://www.cisco.com/univercd/cc/td/doc/product/access/acs_serv/as5800/sw_conf/58_oamp/index.htm
Cisco IOS Dial Technologies Configuration Guide
http://www.cisco.com/univercd/cc/cc/td/doc/product/software/ios122/122cgcr/fdial_c/index.htm
Cisco IOS Dial Technologies Command Reference
http://www.cisco.com/univercd/cc/cc/td/doc/product/software/ios122/122cgcr/fdial_r/index.htm
Cisco SS7 Interconnect for Access Servers Solution
http://www.cisco.com/univercd/cc/td/doc/product/access/sc/rel7/soln/das22/index.htm
Cisco SS7 Dial Access Solution System Integration
http://www.cisco.com/univercd/cc/td/doc/product/access/sc/r1/
Cisco SC2200 Signaling Controller documentation
http://www.cisco.com/univercd/cc/td/doc/product/access/sc/r2/
Standards
MIBs
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To locate and download MIBs for selected platforms, Cisco software releases, and feature sets, use Cisco MIB Locator found at the following URL:
RFCs
Feature Information for Router-Shelf Redundancy for the Cisco AS5800
Table 1 lists the release history for this feature.
Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
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Glossary
DSC—dial-shelf controller.
DSIP—Dial Shelf Interconnection Protocol.
RLM—redundant link manager.
RPM—resource pool management.
RPMS—resource pool manager server.
SDP—Session Definition Protocol.
SNMP—Simple Network Management Protocol.
SS7—Signaling System 7.
Cisco and the Cisco Logo are trademarks of Cisco Systems, Inc. and/or its affiliates in the U.S. and other countries. A listing of Cisco's trademarks can be found at www.cisco.com/go/trademarks. Third party trademarks mentioned are the property of their respective owners. The use of the word partner does not imply a partnership relationship between Cisco and any other company. (1005R)
Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental
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