Cisco Nonstop Forwarding

Transcription

1 Cisco Nonstop Forwarding Feature History Release Modification 12.0(22)S This feature was introduced. 12.0(23)S Support was added for 1xGE and 3xGE line cards on the 12.0(24)S Support was added for the following line cards on the Engine 1 2-port OC-12/STM-4c DPT Engine 2 1-port OC-48/STM-16c DPT 8-port OC-3/STM-1c ATM IP Service Engine (ISE) 4-port OC-3c/STM-1c POS/SDH ISE 8-port OC-3c/STM-1c POS/SDH ISE 16-port OC-3c/STM-1c POS/SDH ISE 4-port OC-12c/STM-4c POS/SDH ISE 1-port OC-48c/STM-16c POS/SDH ISE 4-port channelized OC-12/STM-4 (DS3/E3, OC-3c/STM-1c) POS/SDH ISE 1-port channelized OC-48/STM-16 (DS3/E3, OC-3c/STM-1c) POS/SDH ISE Supported Platforms For platforms supported in Cisco IOS Release 12.0(22)S, 12.0(23)S, and 12.0(24)S, consult Cisco Feature Navigator. This document describes the Cisco Nonstop Forwarding (NSF) feature in Cisco IOS Release 12.0(24)S. It includes the following sections: Feature Overview, page 2 Supported Platforms, page 8 Supported Standards, MIBs, and RFCs, page 9 Prerequisites, page 9 1

2 Feature Overview Cisco Nonstop Forwarding Configuration Tasks, page 10 Configuration Examples, page 17 Command Reference, page 18 Note Throughout this document, the term Route Processor (RP) is used to describe the route processing engine on all networking devices, regardless of the platform designation, unless otherwise noted. For example, on the Cisco series Internet router the RP is referred to as the Performance Routing Engine (PRE), on the Cisco series Internet router the RP is referred to as the Gigabit Route Processor (GRP), and on the Cisco 7500 series router the RP is referred to as the Route Switch Processor (RSP). Feature Overview Cisco NSF works with the Stateful Switchover (SSO) feature in Cisco IOS software. SSO is a prerequisite of Cisco NSF. NSF works with SSO to minimize the amount of time a network is unavailable to its users following a switchover. The main objective of Cisco NSF is to continue forwarding IP packets following a route processor (RP) switchover. Usually, when a networking device restarts, all routing peers of that device detect that the device went down and then came back up. This transition results in what is called a routing flap, which could spread across multiple routing domains. Routing flaps caused by routing restarts create routing instabilities, which are detrimental to the overall network performance. Cisco NSF helps to suppress routing flaps in SSO-enabled devices, thus reducing network instability. Cisco NSF allows for the forwarding of data packets to continue along known routes while the routing protocol information is being restored following a switchover. With Cisco NSF, peer networking devices do not experience routing flaps. Data traffic is forwarded through intelligent line cards or dual forwarding processors (FPs) while the standby RP assumes control from the failed active RP during a switchover. The ability of line cards and FPs to remain up through a switchover and to be kept current with the Forwarding Information Base (FIB) on the active RP is key to Cisco NSF operation. SSO Dependency Cisco NSF always runs together with SSO. This section provides some background information on the SSO feature. In specific Cisco networking devices that support dual RPs, SSO establishes one of the RPs as the active processor while the other RP is designated as the standby processor, and then synchronizes information between them. A switchover from the active to the standby processor occurs when the active RP fails, is removed from the networking device, or is manually taken down for maintenance. In networking devices running SSO, both RPs must be running the same configuration so that the standby RP is always ready to assume control following a fault on the active RP. The configuration information is synchronized from the active RP to the standby RP at startup and whenever changes to the active RP configuration occur. Following an initial synchronization between the two processors, SSO maintains RP state information between them, including forwarding information. During switchover, system control and routing protocol execution is transferred from the active processor to the standby processor. The time required by the device to switch over from the active to the standby processor ranges from just a few seconds to approximately 30 seconds, depending on the platform. 2

3 Cisco Nonstop Forwarding Feature Overview SSO supported protocols and applications must be high-availability (HA)-aware. A feature or protocol is HA aware if it maintains, either partially or completely, undisturbed operation through an RP switchover. For some HA aware protocols and applications, state information is synchronized from the active to the standby processor. For Cisco NSF, enhancements to the routing protocols (Cisco Express Forwarding, or CEF; Open Shortest Path First, or OSPF; Border Gateway Protocol, or BGP; and Intermediate System-to-Intermediate System, or IS-IS) have been made to support the HA features in SSO. For more information on SSO, see the section Related Documents. Cisco NSF Routing and Forwarding Operation Cisco NSF is supported by the BGP, OSPF, and IS-IS protocols for routing and by Cisco Express Forwarding (CEF) for forwarding. Of the routing protocols, BGP, OSPF, and IS-IS have been enhanced with NSF-capability and awareness, which means that routers running these protocols can detect a switchover and take the necessary actions to continue forwarding network traffic and to recover route information from the peer devices. The IS-IS protocol can be configured to use state information that has been synchronized between the active and the standby RP to recover route information following a switchover instead of information received from peer devices. In this document, a networking device is said to be NSF-aware if it is running NSF-compatible software. A device is said to be NSF-capable if it has been configured to support NSF; therefore, it would rebuild routing information from NSF-aware or NSF-capable neighbors. Each protocol depends on CEF to continue forwarding packets during switchover while the routing protocols rebuild the Routing Information Base (RIB) tables. Once the routing protocols have converged, CEF updates the FIB table and removes stale route entries. CEF, in turn, updates the line cards with the new FIB information. Table 1 lists the routing protocol and CEF support in Cisco NSF. Table 1 Routing Protocol and CEF Support in Cisco NSF NSF Support in Cisco IOS Software Release Protocol Platform 12.0(22)S 12.0(23)S 12.0(24)S BGP Cisco 7200 Yes 1 Yes 1 Yes 1 Cisco 7500 Yes Yes Yes Cisco Yes Yes Yes Cisco Yes Yes Yes OSPF Cisco 7200 Yes 1 Yes 1 Yes 1 Cisco 7500 Yes Yes Yes Cisco Yes Yes Yes Cisco Yes Yes Yes IS-IS Cisco 7200 Yes 1 Yes Yes 1 Cisco 7500 Yes Yes Yes Cisco Yes Yes Yes Cisco Yes Yes Yes 3

4 Feature Overview Cisco Nonstop Forwarding Table 1 Routing Protocol and CEF Support in Cisco NSF Protocol Platform NSF Support in Cisco IOS Software Release 12.0(22)S 12.0(23)S 12.0(24)S CEF Cisco 7200 N/A 2 N/A 2 Cisco 7500 Yes Yes Yes Cisco Yes Yes Yes Cisco Yes Yes Yes 1. The Cisco 7200 is a single-route processor system and cannot maintain its forwarding table in the event of a route processor failure. It cannot perform nonstop forwarding of packets. However, it supports the NSF protocol extensions for BGP, OSPF, and ISIS. Therefore, it can peer with NSF-capable routers and facilitate the resynchronization of routing information with such routers. 2. The Cisco 7200 is a single processor device and does not support SSO; therefore, CEF support for NSF does not apply. Cisco Express Forwarding A key element of NSF is packet forwarding. In a Cisco networking device, packet forwarding is provided by CEF. CEF maintains the FIB, and uses the FIB information that was current at the time of the switchover to continue forwarding packets during a switchover. This feature reduces traffic interruption during the switchover. During normal NSF operation, CEF on the active RP synchronizes its current FIB and adjacency databases with the FIB and adjacency databases on the standby RP. Upon switchover of the active RP, the standby RP initially has FIB and adjacency databases that are mirror images of those that were current on the active RP. For platforms with intelligent line cards, the line cards will maintain the current forwarding information over a switchover; for platforms with forwarding engines, CEF will keep the forwarding engine on the standby RP current with changes that are sent to it by CEF on the active RP. In this way, the line cards or forwarding engines will be able to continue forwarding after a switchover as soon as the interfaces and a data path are available. As the routing protocols start to repopulate the RIB on a prefix-by-prefix basis, the updates in turn cause prefix-by-prefix updates to CEF, which it uses to update the FIB and adjacency databases. Existing and new entries will receive the new version ( epoch ) number, indicating that they have been refreshed. The forwarding information is updated on the line cards or forwarding engine during convergence. The RP signals when the RIB has converged. The software removes all FIB and adjacency entries that have an epoch older than the current switchover epoch. The FIB now represents the newest routing protocol forwarding information. Routing Protocols The routing protocols run only on the active RP, and they receive routing updates from their neighbor routers. Routing protocols do not run on the standby RP. Following a switchover, the routing protocols request that the NSF-aware neighbor devices send state information to help rebuild the routing tables. Alternately, the IS-IS protocol can be configured to synchronize state information from the active to the standby RP to help rebuild the routing table on the NSF-capable device in environments where neighbor devices are not NSF-aware. Note For NSF operation, the routing protocols depend on CEF to continue forwarding packets while the routing protocols rebuild the routing information. 4

5 Cisco Nonstop Forwarding Feature Overview BGP Operation When a NSF-capable router begins a BGP session with a BGP peer, it sends an OPEN message to the peer. Included in the message is a declaration that the NSF-capable device has graceful restart capability. Graceful restart is the mechanism by which BGP routing peers avoid a routing flap following a switchover. If the BGP peer has received this capability, it is aware that the device sending the message is NSF-capable. Both the NSF-capable router and its BGP peer(s) need to exchange the Graceful Restart Capability in their OPEN messages, at the time of session establishment. If both the peers do not exchange the Graceful Restart Capability, the session will not be graceful restart capable. If the BGP session is lost during the RP switchover, the NSF-aware BGP peer marks all the routes associated with the NSF-capable router as stale; however, it continues to use these routes to make forwarding decisions for a set period of time. This functionality means that no packets are lost while the newly active RP is waiting for convergence of the routing information with the BGP peers. After an RP switchover occurs, the NSF-capable router reestablishes the session with the BGP peer. In establishing the new session, it sends a new graceful restart message that identifies the NSF-capable router as having restarted. At this point, the routing information is exchanged between the two BGP peers. Once this exchange is complete, the NSF-capable device uses the routing information to update the RIB and the FIB with the new forwarding information. The NSF-aware device uses the network information to remove stale routes from its BGP table. Following that, the BGP protocol is fully converged. If a BGP peer does not support the graceful restart capability, it will ignore the graceful-restart capability in an OPEN message but will establish a BGP session with the NSF-capable device. This function will allow interoperability with non-nsf-aware BGP peers (and without NSF functionality), but the BGP session with non-nsf-aware BGP peers will not be graceful restart capable. Note BGP support in NSF requires that neighbor networking devices be NSF-aware; that is, the devices must have the Graceful Restart Capability and advertise that capability in their OPEN message during session establishment. If an NSF-capable router discovers that a particular BGP neighbor does not have Graceful Restart Capability, it will not establish an NSF-capable session with that neighbor. All other neighbors that have Graceful Restart Capability will continue to have NSF-capable sessions with this NSF-capable networking device. OSPF Operation When an OSPF NSF-capable router performs an RP switchover, it must perform two tasks in order to resynchronize its Link State Database with its OSPF neighbors. First, it must relearn the available OSPF neighbors on the network without causing a reset of the neighbor relationship. Second, it must reacquire the contents of the Link State Database for the network. As quickly as possible after an RP switchover, the NSF-capable router sends an OSPF NSF signal to neighboring NSF-aware devices. Neighbor networking devices recognize this signal as a cue that the neighbor relationship with this router should not be reset. As the NSF-capable router receives signals from other routers on the network, it can begin to rebuild its neighbor list. Once neighbor relationships are reestablished, the NSF-capable router begins to resynchronize its database with all of its NSF-aware neighbors. At this point, the routing information is exchanged between the OSPF neighbors. Once this exchange is complete, the NSF-capable device uses the routing information to remove stale routes, update the RIB, and update the FIB with the new forwarding information. The OSPF protocols are then fully converged. 5

6 Feature Overview Cisco Nonstop Forwarding Note OSPF NSF requires that all neighbor networking devices be NSF-aware. If an NSF-capable router discovers that it has non-nsf -aware neighbors on a particular network segment, it will disable NSF capabilities for that segment. Other network segments composed entirely of NSF-capable or NSF-aware routers will continue to provide NSF capabilities. IS-IS Operation When an IS-IS NSF-capable router performs an RP switchover, it must perform two tasks in order to resynchronize its Link State Database with its IS-IS neighbors. First, it must relearn the available IS-IS neighbors on the network without causing a reset of the neighbor relationship. Second, it must reacquire the contents of the Link State Database for the network. The IS-IS NSF feature offers two options when configuring NSF: Internet Engineering Task Force (IETF) IS-IS Cisco IS-IS If neighbor routers on a network segment are NSF-aware, meaning that neighbor routers are running a software version that supports the IETF Internet draft for router restartability, they will assist an IETF NSF router which is restarting. With IETF, neighbor routers provide adjacency and link-state information to help rebuild the routing information following a switchover. A benefit of IETF IS-IS configuration is operation between peer devices based on a proposed standard. Note If you configure IETF on the networking device, but neighbor routers are not IETF-compatible, NSF will abort following a switchover. If the neighbor routers on a network segment are not NSF-aware, you must use the Cisco configuration option. The Cisco IS-IS configuration transfers both protocol adjacency and link-state information from the active to the standby RP. A benefit of Cisco configuration is that it does not rely on NSF-aware neighbors. IETF IS-IS Configuration Using the IETF IS-IS configuration, as quickly as possible after an RP switchover, the NSF-capable router sends IS-IS NSF restart requests to neighboring NSF-aware devices. Neighbor networking devices recognize this restart request as a cue that the neighbor relationship with this router should not be reset, but that they should initiate database resynchronization with the restarting router. As the restarting router receives restart request responses from routers on the network, it can begin to rebuild its neighbor list. Once this exchange is complete, the NSF-capable device uses the link-state information to remove stale routes, update the RIB, and update the FIB with the new forwarding information. IS-IS is then fully converged. The switchover from one RP to the other happens within seconds. IS-IS reestablishes its routing table and resynchronizes with the network within a few additional seconds. At this point, IS-IS waits for a specified interval before it will attempt a second NSF restart. During this time, the new standby RP will boot up and synchronize its configuration with the active RP. The IS-IS NSF operation waits for a specified interval to ensure that connections are stable before attempting another restart of IS-IS NSF. This functionality prevents IS-IS from attempting back-to-back NSF restarts with stale information. 6

7 Cisco Nonstop Forwarding Feature Overview Cisco IS-IS Configuration Using the Cisco configuration option, full adjacency and LSP information is saved, or checkpointed, to the standby RP. Following a switchover, the newly active RP maintains its adjacencies using the checkpointed data, and can quickly rebuild its routing tables. Note Following a switchover, Cisco IS-IS NSF has complete neighbor adjacency and LSP information; however, it must wait for all interfaces that had adjacencies prior to the switchover to come up. If an interface does not come up within the allocated interface wait time, the routes learned from these neighbor devices are not considered in routing table recalculation. IS-IS NSF provides a command to extend the wait time for interfaces that, for whatever reason, do not come up in a timely fashion. The switchover from one RP to the other happens within seconds. IS-IS reestablishes its routing table and resynchronizes with the network within a few additional seconds. At this point, IS-IS waits for a specified interval before it will attempt a second NSF restart. During this time, the new standby RP will boot up and synchronize its configuration with the active RP. Once this synchronization is completed, IS-IS adjacency and LSP data is checkpointed to the standby RP; however, a new NSF restart will not be attempted by IS-IS until the interval time expires. This functionality prevents IS-IS from attempting back-to-back NSF restarts. Benefits Improved Network Availability NSF continues forwarding network traffic and application state information so that user session information is maintained after a switchover. Overall Network Stability Network stability may be improved with the reduction in the number of route flaps that had been created when routers in the network failed and lost their routing tables. Neighboring Routers Do Not Detect a Link Flap Because the interfaces remain up across a switchover, neighboring routers do not detect a link flap (the link does not go down and come back up). Prevents Routing Flaps Because SSO continues forwarding network traffic in the event of a switchover, routing flaps are avoided. No Loss of User Sessions User sessions established prior to the switchover are maintained. Restrictions General Restrictions For NSF operation, you must have SSO configured on the device. The Hot Standby Routing Protocol (HSRP) is not supported with Cisco Nonstop Forwarding with Stateful Switchover. Do not use HSRP with Cisco Nonstop Forwarding with Stateful Switchover. 7

8 Supported Platforms Cisco Nonstop Forwarding BGP NSF All neighboring devices participating in BGP NSF must be NSF-capable, having been configured for BGP graceful restart as specified in the Configuring BGP NSF section. OSPF NSF OSPF NSF for virtual links is not supported. All OSPF networking devices on the same network segment must be NSF-aware (running an NSF software image). IS-IS NSF For IETF IS-IS, all neighboring devices must be running an NSF-aware software image. Cisco 7200 Series Router The Cisco 7200 series router has a single CPU; therefore, it cannot support the stateful switchover in the event of a network processor engine (NPE) fault. The Cisco 7206 does support NSF and can operate in a peer role with a Cisco 7500, 10000, or series router running. With NSF enabled, an RP switchover on the Cisco 7500, 10000, or series router peer should not cause a loss of PPP, ATM, high-level data link control (HDLC), or Frame Relay sessions, or a loss of any OSPF, BGP, or IS-IS adjacencies established between the Cisco 7200 and the peer. Related Features and Technologies Stateful Switchover BGP OSPF IS-IS CEF Related Documents Stateful Switchover, feature module Cisco IOS Network Protocols Configuration Guide, Part 1, Release 12.0 Cisco IOS Switching Services Configuration Guide, Release 12.0 Supported Platforms Determining Platform Support Through Cisco Feature Navigator Cisco IOS software is packaged in feature sets that are supported on specific platforms. To obtain updated information about platform support for this feature, access Cisco Feature Navigator. Cisco Feature Navigator dynamically updates the list of supported platforms as new platform support is added for the feature. 8

9 Cisco Nonstop Forwarding Supported Standards, MIBs, and RFCs Cisco Feature Navigator is a web-based tool that enables you to determine which Cisco IOS software images support a specific set of features and which features are supported in a specific Cisco IOS image. You can search by feature or release. In the release section, you can compare releases side by side to display both the features unique to each software release and the features that releases have in common. To access Cisco Feature Navigator, you must have an account on Cisco.com. If you have forgotten or lost your account information, send a blank to cco-locksmith@cisco.com. An automatic check will verify that your address is registered with Cisco.com. If the check is successful, account details with a new random password will be ed to you. Qualified users can establish an account on Cisco.com by following the directions at Cisco Feature Navigator is updated regularly when major Cisco IOS software releases and technology releases occur. For the most current information, go to the Cisco Feature Navigator home page at the following URL: Availability of Cisco IOS Software Images Platform support for particular Cisco IOS software releases is dependent on the availability of the software images for those platforms. Software images for some platforms may be deferred, delayed, or changed without prior notice. For updated information about platform support and availability of software images for each Cisco IOS software release, refer to the online release notes or, if supported, Cisco Feature Navigator. Supported Standards, MIBs, and RFCs Standards Restart Signaling for ISIS, Internet Engineering Task Force (IETF) Network Working Group Internet Draft, September 2001 MIBs Graceful Restart Mechanism for BGP (draft-ietf-idr-restart-05.txt) To obtain lists of supported MIBs by platform and Cisco IOS release, and to download MIB modules, go to the Cisco MIB website on Cisco.com at the following URL: RFCs No new or modified RFCs are supported by this feature. Prerequisites NSF must be configured on a networking device that has been configured for SSO. On platforms supporting the Route Switch Processor (RSP), and where the CEF switching mode is configurable, configure distributed CEF (dcef) switching mode using the ip cef distributed command. 9

10 Configuration Tasks Cisco Nonstop Forwarding Configuration Tasks See the following sections for configuration tasks for the SSO feature. Each task in the list is identified as either required or optional. Configuring CEF NSF (required) Configuring BGP NSF (required) Configuring OSPF NSF (required) Configuring IS-IS NSF (required) Verifying CEF NSF (optional) Verifying BGP NSF (optional) Verifying OSPF NSF (optional) Verifying IS-IS NSF (optional) Configuring CEF NSF The CEF NSF feature operates by default while the networking device is running in SSO mode. No configuration is necessary. Configuring BGP NSF Note You must configure BGP graceful restart on all peer devices participating in BGP NSF. To configure BGP for NSF, use the following commands beginning in privileged EXEC mode, and repeat this procedure on each of the BGP NSF peer devices: Command Purpose Step 1 Router# configure terminal Enters global configuration mode. Step 2 Router(config)# router bgp as-number Enables a BGP routing process, which places the router in router configuration mode. Step 3 Router(config-router)# bgp graceful-restart Enables the BGP graceful restart capability, starting NSF for BGP. If you enter this command after the BGP session has been established, you must restart the session for the capability to be exchanged with the BGP neighbor. Use this command on the restarting router and all of its peers. 10

11 Cisco Nonstop Forwarding Configuration Tasks Configuring OSPF NSF Note All peer devices participating in OSPF NSF must be made OSPF NSF-aware, which happens automatically once you install an NSF software image on the device. To configure NSF for OSPF, use the following commands beginning in privileged EXEC mode: Command Purpose Step 1 Router# configure terminal Enters global configuration mode. Step 2 Router(config)# router ospf processid Enables an OSPF routing process, which places the router in router configuration mode. Step 3 Router(config-router)# nsf Enables NSF operations for OSPF. Configuring IS-IS NSF To configure NSF for IS-IS, use the following commands beginning in privileged EXEC mode: Command Purpose Step 1 Router# configure terminal Enters global configuration mode. Step 2 Router(config)# router isis [tag] Enables an IS-IS routing process, which places the router in router configuration mode. Step 3 Router(config-router)# nsf [cisco ietf] Enables NSF operation for IS-IS. Enter the ietf keyword to enable IS-IS in homogeneous network where adjacencies with networking devices supporting IETF draft-based restartability is guaranteed. Enter the cisco keyword to run IS-IS in heterogeneous networks that might not have adjacencies with NSF-aware networking devices. Step 4 Router(config-router)# nsf interval [minutes] (Optional) Specifies the minimum time between NSF restart attempts. The default time between consecutive NSF restart attempts is 5 minutes. 11

12 Configuration Tasks Cisco Nonstop Forwarding Command Step 5 Router(config-router)# nsf t3 {manual [seconds] adjacency} Purpose (Optional) Specifies the time IS-IS will wait for the IS-IS database to synchronize before generating overloaded link-state information for itself and flooding that information out to its neighbors. The t3 keyword applies only if you selected IETF operation. Specifying adjacency means that the restarting router obtains its wait time from neighboring devices. Step 6 Router(config-router)# nsf interface wait seconds (Optional) Specifies how long an IS-IS NSF restart will wait for all interfaces with IS-IS adjacencies to come up before completing the restart. The default is 10 seconds. Verifying CEF NSF To verify that CEF is NSF-capable, use the show cef state command: router# show cef state CEF Status [RP] CEF enabled/running dcef enabled/running CEF switching enabled/running CEF default capabilities: Always FIB switching: yes Default CEF switching: yes Default dcef switching: yes Update HWIDB counters: no Drop multicast packets: no... CEF NSF capable: yes IPC delayed func on SSO: no RRP state: I am standby RRP: no My logical slot: 0 RF PeerComm: no Verifying BGP NSF To verify NSF for BGP, you must check that the graceful restart function is configured on the SSO-enabled networking device and on the neighbor devices. Perform the following steps: Step 1 Verify that bgp graceful-restart appears in the BGP configuration of the SSO-enabled router by entering the show running-config command: Router# show running-config... router bgp

13 Cisco Nonstop Forwarding Configuration Tasks... bgp graceful-restart neighbor remote-as Step 2 Step 3 Repeat step 1 on each of the BGP neighbors. On the SSO device and the neighbor device, verify that the graceful restart function is shown as both advertised and received, and confirm the address families that have the graceful restart capability. If no address families are listed, then BGP NSF also will not occur: router#show ip bgp neighbors x.x.x.x BGP neighbor is , remote AS YY, external link BGP version 4, remote router ID BGP state = Established, up for 00:01:18 Last read 00:00:17, hold time is 180, keepalive interval is 60 seconds Neighbor capabilities: Route refresh:advertised and received(new) Address family IPv4 Unicast:advertised and received Address famiiy IPv4 Multicast:advertised and received Graceful Restart Capabilty:advertised and received Remote Restart timer is 120 seconds Address families preserved by peer: IPv4 Unicast, IPv4 Multicast Received 1539 messages, 0 notifications, 0 in queue Sent 1544 messages, 0 notifications, 0 in queue Default minimum time between advertisement runs is 30 seconds Verifying OSPF NSF To verify NSF for OSPF, you must check that the NSF function is configured on the SSO-enabled networking device. Perform the following steps: Step 1 Verify that nsf appears in the OSPF configuration of the SSO-enabled device by entering the show running-config command: Router# show running-config router ospf 120 log-adjacency-changes nsf network area 0 network area 1 network area 2... Step 2 Use the show ip ospf command to verify that NSF is enabled on the device: router> show ip ospf Routing Process "ospf 1" with ID and Domain ID Supports only single TOS(TOS0) routes Supports opaque LSA 13

14 Configuration Tasks Cisco Nonstop Forwarding SPF schedule delay 5 secs, Hold time between two SPFs 10 secs Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs Number of external LSA 0. Checksum Sum 0x0 Number of opaque AS LSA 0. Checksum Sum 0x0 Number of DCbitless external and opaque AS LSA 0 Number of DoNotAge external and opaque AS LSA 0 Number of areas in this router is 1. 1 normal 0 stub 0 nssa External flood list length 0 Non-Stop Forwarding enabled, last NSF restart 00:02:06 ago (took 44 secs) Area BACKBONE(0) Number of interfaces in this area is 1 (0 loopback) Area has no authentication SPF algorithm executed 3 times Verifying IS-IS NSF To verify NSF for IS-IS, you must check that the NSF function is configured on the SSO-enabled networking device. Perform the following steps: Step 1 Step 2 Verify that nsf appears in the IS-IS configuration of the SSO-enabled device by entering the show running-config command. The display will show either Cisco IS-IS or IETF IS-IS configuration. The following display indicates that the device uses the Cisco implementation of IS-IS NSF: Router# show running-config... router isis nsf cisco... If the NSF configuration is set to cisco, use the show isis nsf command to verify that NSF is enabled on the device. Using the Cisco configuration, the display output will be different on the active and standby RPs. The following display shows sample output for the Cisco configuration on the active RP. In this example, note the presence of NSF restart enabled : router# show isis nsf NSF is ENABLED, mode 'cisco' RP is ACTIVE, standby ready, bulk sync complete NSF interval timer expired (NSF restart enabled) Checkpointing enabled, no errors Local state:active, Peer state:standby HOT, Mode:SSO The following display shows sample output for the Cisco configuration on the standby RP. In this example, note the presence of NSF restart enabled : router# show isis nsf NSF enabled, mode 'cisco' RP is STANDBY, chkpt msg receive count:adj 2, LSP 7 NSF interval timer notification received (NSF restart enabled) Checkpointing enabled, no errors Local state:standby HOT, Peer state:active, Mode:SSO 14

15 Cisco Nonstop Forwarding Configuration Tasks Step 3 If the NSF configuration is set to ietf, enter the show isis nsf command to verify that NSF is enabled on the device. The following display shows sample output for the IETF IS-IS configuration on the networking device: router# show isis nsf NSF is ENABLED, mode IETF NSF pdb state:inactive NSF L1 active interfaces:0 NSF L1 active LSPs:0 NSF interfaces awaiting L1 CSNP:0 Awaiting L1 LSPs: NSF L2 active interfaces:0 NSF L2 active LSPs:0 NSF interfaces awaiting L2 CSNP:0 Awaiting L2 LSPs: Interface:Serial3/0/2 NSF L1 Restart state:running NSF p2p Restart retransmissions:0 Maximum L1 NSF Restart retransmissions:3 L1 NSF ACK requested:false L1 NSF CSNP requested:false NSF L2 Restart state:running NSF p2p Restart retransmissions:0 Maximum L2 NSF Restart retransmissions:3 L2 NSF ACK requested:false Interface:GigabitEthernet2/0/0 NSF L1 Restart state:running NSF L1 Restart retransmissions:0 Maximum L1 NSF Restart retransmissions:3 L1 NSF ACK requested:false L1 NSF CSNP requested:false NSF L2 Restart state:running NSF L2 Restart retransmissions:0 Maximum L2 NSF Restart retransmissions:3 L2 NSF ACK requested:false L2 NSF CSNP requested:false Interface:Loopback1 NSF L1 Restart state:running NSF L1 Restart retransmissions:0 Maximum L1 NSF Restart retransmissions:3 L1 NSF ACK requested:false L1 NSF CSNP requested:false NSF L2 Restart state:running NSF L2 Restart retransmissions:0 Maximum L2 NSF Restart retransmissions:3 L2 NSF ACK requested:false L2 NSF CSNP requested:false Troubleshooting Tips To troubleshoot the NSF feature, use the following commands in privileged EXEC mode, as needed: 15

16 Configuration Tasks Cisco Nonstop Forwarding Command Router# clear cef epoch Router# debug isis nsf [detail] Router# debug ospf nsf [detail] Router# show cef nsf Router# show cef state Router# show clns neighbors Router> show ip bgp Router# show ip bgp neighbor Router# show ip cef Router> show ip ospf Router> show ip ospf neighbor [detail] Router# show isis database [detail] Router# show isis nsf Purpose Begins a new epoch and increments the epoch number for a CEF table. Displays information about the IS-IS state during a Cisco NSF restart. Displays debugging messages related to OSPF Cisco NSF commands. Displays the current NSF state of CEF on both the active and standby RPs. Displays the state of CEF on a networking device. Display both end-system (ES) and intermediate system (IS) neighbors. Displays entries in the BGP routing table. Displays information about the TCP and BGP connections to neighbor devices. Displays entries in the FIB that are unresolved, or displays a FIB summary. Displays general information about OSPF routing processes. Displays OSPF-neighbor information on a per-interface basis. Displays the IS-IS link-state database. Displays the current state information regarding IS-IS Cisco NSF. The following tips may help you to troubleshoot the device. The system displays FIB errors. Use the show cef state command to verify that distributed CEF switching is enabled on your platform. To enable distributed CEF, enter the ip cef distributed command in global configuration mode on the active RP. Note For Cisco series Internet routers and Cisco series Internet routers, distributed CEF is always enabled and is not configurable. Cannot determine if an OSPF neighbor is NSF-aware. To verify whether an OSPF neighbor device is NSF-aware and if NSF is operating between them, use the show ip ospf neighbor detail command. The system loses, or appears to lose, adjacencies with network peers following a stateful switchover. Use the show clns neighbors detail command to find any neighbors that do not have NSF capable and make sure that they are running NSF-aware images. 16

17 Cisco Nonstop Forwarding Configuration Examples Additionally, for ISIS, the standby RP must be stable for 5 minutes (default) before another restart can be initiated. Use the nsf interval command to reset the restart period. Configuration Examples This section provides the following configuration examples: Configuring BGP NSF Example Configuring BGP NSF Neighbor Device Example Configuring OSPF NSF Example Configuring IS-IS NSF Example Configuring BGP NSF Example The following example configures BGP NSF on a networking device: router# configure terminal router(config)# router bgp 590 router(config-router)# bgp graceful-restart Configuring BGP NSF Neighbor Device Example The following example configures BGP NSF on a neighbor router. All devices supporting BGP NSF must be NSF-aware, meaning that these devices recognize and advertise graceful restart capability. router# configure terminal router(config)# router bgp 770 router(config-router)# bgp graceful-restart Configuring OSPF NSF Example The following example configures OSPF NSF on a networking device: router# configure terminal router(config)# router ospf 400 router(config-router)# nsf Configuring IS-IS NSF Example The following example configures Cisco proprietary IS-IS NSF operation on a networking device: router# configure terminal router(config)# router isis router(config-router)# nsf cisco The following example configures IS-IS NSF for IETF operation on a networking device: router# configure terminal router(config)# router isis router(config-router)# nsf ietf 17

18 Command Reference Cisco Nonstop Forwarding Command Reference This section documents new and modified commands. All other commands used with this feature are documented in the Cisco IOS high-availability command reference publications for various releases. New Commands bgp graceful-restart debug ip ospf nsf debug isis nsf nsf (IS-IS) nsf (OSPF) nsf interface wait nsf interval nsf t3 show cef nsf show cef state show isis nsf Modified Commands clear ip cef epoch show clns neighbors show ip bgp show ip bgp neighbors show ip cef show ip ospf show ip ospf neighbor 18

19 Cisco Nonstop Forwarding bgp graceful-restart bgp graceful-restart To enable the Border Gateway Protocol (BGP) graceful restart capability, use the bgp graceful-restart command in router configuration mode. To remove this command from the configuration file and restore the system to its default condition with respect to this command, use the no form of this command. bgp graceful-restart [restart-time seconds stalepath-time seconds] no bgp graceful-restart [restart-time seconds stalepath-time seconds] Syntax restart-time stalepath-time seconds (Optional) Used to set the maximum time to wait for a graceful-restart-capable neighbor to come back up after a restart. The default is 120 seconds. (Optional) Used to set the maximum time to hold on to the stale paths of a gracefully restarted peer. All stale paths are deleted after the expiration of this timer. The default is 360 seconds. (Optional) The restart-time or stalepath-time value in number of seconds. The valid range is from 1 to 3600 seconds. Defaults BGP Cisco Nonstop Forwarding (NSF) is disabled. Command Modes Router configuration Command History Release 12.0(22)S Modification This command was introduced. Usage Guidelines The BGP graceful restart capability is negotiated in the OPEN message. If the user enters the bgp graceful-restart command after the BGP session is established, the session will need to be restarted. When you enter the bgp graceful-restart command, the bgp graceful-restart restart-time and bgp graceful-restart stalepath-time commands are enabled by default. After the bgp graceful-restart command is used to configure the graceful restart capability, you may tune the configuration using the restart-time and stalepath-time keywords. If you do not first configure the graceful restart capability using the bgp graceful-restart command, the tuning values will not appear in the configuration file. We recommend that the bgp graceful-restart restart-time and bgp graceful-restart stalepath-time commands remain set to their default values. 19

20 bgp graceful-restart Cisco Nonstop Forwarding Examples The following example shows how to configure the BGP graceful restart capability. Enter one command per line: Router# configure terminal Router(config)# router bgp Router(config-router)# bgp graceful-restart Router(config-router)# end Related Commands Command show ip bgp Displays entries in the BGP routing table. show ip bgp neighbors Displays information about the TCP and BGP connections to neighbors. 20

21 Cisco Nonstop Forwarding clear ip cef epoch clear ip cef epoch To begin a new epoch and increment the epoch number for a Cisco Express Forwarding (CEF) table, use the clear ip cef epoch command in privileged EXEC mode. To remove this command from the configuration file and restore the system to its default condition with respect to this command, use the no form of this command. clear ip cef epoch [all-vrfs full vrf [name]] no clear ip cef epoch [all-vrfs full vrf [name]] Syntax all-vrfs full vrf name (Optional) Begin a new epoch for all CEF tables. (Optional) Begin a new epoch for all tables, including adjacency tables. (Optional) Begin a new virtual private network (VPN) routing and forwarding instance CEF table. (Optional) VPN VRF instance name. Defaults No default behavior or values. Command Modes Privileged EXEC Command History Release 12.1(8a)EX 12.0(22)S Modification This command was introduced. This command was introduced on Cisco 7500, 10000, series Internet routers. Usage Guidelines Use the clear ip cef epoch command when you want to rebuild a table. This command allows old and new table entries to be distinguished within the same data structure and allows you to retain the old CEF database table while constructing the new table. Examples The following example shows the output before and after you clear the epoch table and increment the epoch number: router# show ip cef epoch CEF epoch information: Table: Default-table Table epoch: 2 (43 entries at this epoch) Adjacency table Table epoch: 2 (5 entries at this epoch) router# clear ip cef epoch full 21

22 clear ip cef epoch Cisco Nonstop Forwarding router# show ip cef epoch CEF epoch information: Table: Default-table Table epoch: 3 (43 entries at this epoch) Adjacency table Table epoch: 3 (5 entries at this epoch) Related Commands Command show cef state Displays the state of CEF. 22

23 Cisco Nonstop Forwarding debug ip ospf nsf debug ip ospf nsf To display debugging messages about Open Shortest Path First (OSPF) during a Cisco Nonstop Forwarding (NSF) restart, use the debug ip ospf nsf command in privileged EXEC mode. To disable the display of debugging output, use the no form of this command. debug ip ospf nsf [detail] no debug ip ospf nsf [detail] Syntax detail (Optional) Displays detailed debug messages. Command Modes Privileged EXEC Command History Release 12.0(22)S Modification This command was introduced. Usage Guidelines Use the debug ip ospf nsf command to diagnose problems with OSPF link-state database (LSDB) resynchronization and NSF operations. Examples The following example shows that OSPF NSF events debugging is enabled: router# debug ip ospf nsf Related Commands Command nsf (OSPF) show ip ospf show ip ospf neighbor Configures NSF operations for OSPF. Displays general information about OSPF routing processes. Displays OSPF-neighbor information on a per-interface basis. 23

24 debug isis nsf Cisco Nonstop Forwarding debug isis nsf To display information about the Intermediate System-to-Intermediate System (IS-IS) state during a Cisco Nonstop Forwarding (NSF) restart, use the debug isis nsf command in EXEC mode. To disable debugging output, use the no form of this command. debug isis nsf [detail] no debug isis nsf [detail] Syntax detail (Optional) Provides detailed debugging information. Command Modes EXEC Command History Release 12.0(22)S Modification This command was introduced. Usage Guidelines Use the debug isis nsf command to display basic information about the IS-IS state during an NSF restart. Use the debug isis nsf detail command to display additional IS-IS state detail during an NSF restart. Examples The following example displays IS-IS state information during an NSF restart: router# debug isis nsf IS-IS NSF events debugging is on The following example displays detailed IS-IS state information during an NSF restart: router# debug isis nsf detail IS-IS NSF events (detailed) debugging is on router# Jan 24 20:04:54.090:%CLNS-5-ADJCHANGE:ISIS:Adjacency to gsr1 (GigabitEthernet2/0/0) Up, Standby adjacency Jan 24 20:04:54.090:ISIS-NSF:ADJ:000C (Gi2/0/0), type 8/1, cnt 0/1, ht 10 (NEW) Jan 24 20:04:54.142:ISIS-NSF:Rcv LSP - L2 000B , seq 251, csum B0DC, ht 120, len 123 (local) Jan 24 20:04:55.510:ISIS-NSF:Rcv LSP - L1 000B , seq 23E, csum D20D, ht 120, len 100 (local) Jan 24 20:04:56.494:ISIS-NSF:ADJ:000C (Gi2/0/0), type 8/0, cnt 0/1, ht 30 Jan 24 20:04:56.502:ISIS-NSF:Rcv LSP - L1 000B , seq 21C, csum 413, ht 120, len 58 (local) Jan 24 20:04:58.230:ISIS-NSF:Rcv LSP - L2 000C , seq 11A, csum E197, ht 1194, len 88 (Gi2/0/0) Jan 24 20:05:00.554:ISIS-NSF:Rcv LSP - L1 000B , seq 23F, csum 1527, ht 120, len 111 (local) 24

25 Cisco Nonstop Forwarding debug isis nsf Related Commands Command nsf (IS-IS) Configures NSF operations for IS-IS. nsf interface wait Specifies how long an NSF restart will wait for all interfaces with IS-IS adjacencies to come up before completing the restart. nsf interval Specifies the minimum time between NSF restart attempts. nsf t3 Specifies the methodology used to determine how long IETF NSF will wait for the LSP database to synchronize before generating overloaded link state information for itself and flooding that information out to its neighbors. show clns neighbors Displays both ES and IS neighbors. show isis nsf Displays current state information regarding IS-IS NSF. 25

26 nsf (IS-IS) Cisco Nonstop Forwarding nsf (IS-IS) To configure Cisco Nonstop Forwarding (NSF) operations for Intermediate System-to-Intermediate System (IS-IS), use the nsf command in router configuration IS-IS mode. To remove this command from the configuration file and restore the system to its default condition with respect to this command, use the no form of this command. nsf [cisco ietf] no nsf [cisco ietf] Syntax cisco ietf (Optional) Enables Cisco proprietary IS-IS NSF. (Optional) Enables IETF IS-IS NSF. Defaults NSF is disabled by default. Command Modes Router configuration IS-IS Command History Release 12.0(22)S Modification This command was introduced. Usage Guidelines The user must configure NSF operation only if a router is expected to perform NSF during restart. The optional cisco keyword enables the use of checkpointing to allow the standby route processor (RP) to restore protocol state when an NSF restart occurs. Examples The following example enables Cisco proprietary IS-IS NSF operation: nsf cisco The following example enables IETF IS-IS NSF operation: nsf ietf Related Commands Command debug isis nsf nsf interface wait nsf interval nsf t3 Displays information about the IS-IS state during an NSF restart. Specifies how long a NSF restart will wait for all interfaces with IS-IS adjacencies to come up before completing the restart. Specifies the minimum time between NSF restart attempts. Specifies the methodology used to determine how long IETF NSF will wait for the LSP database to synchronize before generating overloaded link state information for itself and flooding that information out to its neighbors. 26

27 Cisco Nonstop Forwarding nsf (IS-IS) Command show clns neighbors show isis nsf Displays both ES and IS neighbors. Displays current state information regarding IS-IS NSF. 27

28 nsf (OSPF) Cisco Nonstop Forwarding nsf (OSPF) To configure Cisco Nonstop Forwarding (NSF) operations for Open Shortest Path First (OSPF), use the nsf command in router configuration OSPF mode. To remove this command from the configuration file and restore the system to its default condition with respect to this command, use the no form of this command. nsf [enforce global] no nsf [enforce global] Syntax enforce global (Optional) Cancels NSF restart when non-nsf-aware neighboring networking devices are detected. Defaults NSF is disabled by default. Command Modes Router configuration OSPF Command History Release 12.0(22)S Modification This command was introduced. Usage Guidelines In router configuration mode, enter OSPF mode to enter and use this command. The user must configure NSF operation only if a router is expected to perform NSF during restart. For users to have full NSF benefits, all neighbors of the specified router must be NSF-aware. If non-nsf-aware neighbors are detected on a network interface, NSF restart is aborted on that interface; however, NSF restart will continue on other interfaces. This functionality applies to the default NSF mode of operation when NSF is configured. If the user configures the optional enforce global keywords, NSF restart will be canceled for the entire process when non-nsf-aware neighbors are detected on any network interface during restart. To revert to the default NSF mode, configure the nsf command without any keywords. Examples The following example enters router configuration OSPF mode and cancels the NSF restart for the entire OSPF process if non-nsf-aware neighbors are detected on any network interface during restart: router(config)# router ospf 1 router(config-router)# nsf enforce global Related Commands Command debug ip ospf nsf router ospf Displays debugging messages related to OSPF NSF commands. Enables OSPF routing, which places the router in router configuration mode. 28