- EIGRP
- EIGRP MIB
- EIGRP MPLS VPN PE-CE Site of Origin
- EIGRP Nonstop Forwarding (NSF) Awareness
- EIGRP Prefix Limit Support
- EIGRP Support for Route Map Filtering
- IPv6 Routing: EIGRP Support
- Add Path Support in EIGRP
- EIGRP IPv6 VRF-Lite
- EIGRP Stub Routing
- BFD Support for EIGRP IPv6
- EIGRP Route Tag Enhancements
- EIGRP Wide Metrics
- EIGRP/SAF HMAC-SHA-256 Authentication
- IP EIGRP Route Authentication
- EIGRP Support for 6PE/6VPE
- EIGRP Over the Top
- EIGRP Classic to Named Mode Conversion
- EIGRP IWAN Simplification
- Finding Feature Information
- Prerequisites for EIGRP Nonstop Forwarding Awareness
- Restrictions for EIGRP Nonstop Forwarding Awareness
- Information About EIGRP Nonstop Forwarding Awareness
- How to Modify and Maintain EIGRP Nonstop Forwarding Awareness
- Configuration Examples for EIGRP Nonstop Forwarding Awareness
- Additional References
- Feature Information for EIGRP Nonstop Forwarding Awareness
EIGRP Nonstop Forwarding (NSF) Awareness
Nonstop Forwarding (NSF) awareness allows an NSF-aware router to assist NSF-capable and NSF-aware neighbors to continue forwarding packets during a switchover operation or during a well-known failure condition. The EIGRP Nonstop Forwarding Awareness feature allows an NSF-aware router that is running Enhanced Interior Gateway Routing Protocol (EIGRP) to forward packets along routes known to a router performing a switchover operation or in a well-known failure condition. This capability allows the EIGRP peers of the failing router to retain the routing information that it has advertised and to continue using this information until the failed router resumes normal operation and is able to exchange routing information. The peering session is maintained throughout the entire NSF operation.
- Finding Feature Information
- Prerequisites for EIGRP Nonstop Forwarding Awareness
- Restrictions for EIGRP Nonstop Forwarding Awareness
- Information About EIGRP Nonstop Forwarding Awareness
- How to Modify and Maintain EIGRP Nonstop Forwarding Awareness
- Configuration Examples for EIGRP Nonstop Forwarding Awareness
- Additional References
- Feature Information for EIGRP Nonstop Forwarding Awareness
Finding Feature Information
Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the feature information table.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Prerequisites for EIGRP Nonstop Forwarding Awareness
Your network is configured to run EIGRP.
An NSF-aware router must be up and completely converged with the network before it can assist an NSF-capable router in an NSF restart operation.
A version of Cisco IOS that supports NSF awareness or NSF capabilities must be installed.
Restrictions for EIGRP Nonstop Forwarding Awareness
All neighboring devices participating in EIGRP NSF must be NSF-capable or NSF-aware.
EIGRP NSF awareness does not support two neighbors performing an NSF restart operation at the same time. However, both neighbors can reestablish peering sessions after the NSF restart operation is completed.
Information About EIGRP Nonstop Forwarding Awareness
- Cisco NSF Routing and Forwarding Operation
- Cisco Express Forwarding
- EIGRP Nonstop Forwarding Awareness
- EIGRP NSF Capable and NSF Aware Interoperation
- Non-NSF Aware EIGRP Neighbors
- EIGRP NSF Route-Hold Timers
Cisco NSF Routing and Forwarding Operation
Cisco NSF is supported by the BGP, EIGRP, 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 route processor (RP) to recover route information following a switchover instead of information received from peer devices.
In this document, a networking device that is NSF-aware is running NSF-compatible software. A device that is NSF-capable has been configured to support NSF; therefore, the device rebuilds 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. After the routing protocols have converged, CEF updates the forwarding information base (FIB) table and removes stale route entries. CEF, in turn, updates the line cards with the new FIB information.
Cisco Express Forwarding
In a Cisco networking device, CEF provides packet forwarding, a key element of NSF. CEF maintains the FIB and uses the FIB information that was current at the time of a switchover to continue forwarding packets during the switchover. NSF helps to reduce 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 for 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
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.
Note | For NSF operation, the routing protocols depend on CEF to continue forwarding packets while the routing protocols rebuild the routing information. |
EIGRP Nonstop Forwarding Awareness
NSF awareness allows a router that is running EIGRP to assist NSF-capable neighbors to continue forwarding packets during a switchover operation or well-known failure condition. The EIGRP Nonstop Forwarding Awareness feature provides EIGRP with the capability to detect a neighbor that is undergoing an NSF restart event (RP switchover operation) or well-known failure condition, maintain the peering session with this neighbor, retain known routes, and continue to forward packets for these routes. The deployment of EIGRP NSF awareness can minimize the effects of the following:
Well-known failure conditions (for example, a stuck-in-active event)
Unexpected events (for example, an RP switchover operation)
Scheduled events (for example, a hitless software upgrade)
EIGRP NSF awareness is enabled by default and is transparent to the network operator and EIGRP peers that do not support NSF capabilities.
Note | An NSF-aware router must be up and completely converged with the network before it can assist an NSF-capable router in an NSF restart operation. |
EIGRP NSF Capable and NSF Aware Interoperation
EIGRP NSF capabilities are exchanged by EIGRP peers in hello packets. An NSF-capable router notifies its neighbors that an NSF restart operation has started by setting the restart (RS) bit in a hello packet. When an NSF-aware router receives notification from an NSF-capable neighbor that an NSF-restart operation is in progress, both routers immediately exchange their topology tables. The NSF-aware router sends an end-of-table (EOT) update packet when the transmission of its topology table is complete. The NSF-aware router then performs the following actions to assist the NSF-capable router:
Expires the EIGRP hello hold timer to reduce the time interval set for hello packet generation and transmission. This allows the NSF-aware router to reply to the NSF-capable router more quickly and reduces the amount of time required for the NSF-capable router to rediscover neighbors and rebuild the topology table.
Starts the route-hold timer. This timer is used to set the period of time that the NSF-aware router will hold known routes for the NSF-capable neighbor. This timer is configured with the timers graceful-restart purge-timecommand. The default time period is 240 seconds.
Notes in the peer list that the NSF-capable neighbor is restarting, maintains adjacency, and holds known routes for the NSF-capable neighbor until the neighbor signals that it is ready for the NSF-aware router to send its topology table or the route-hold timer expires. If the route-hold timer expires on the NSF-aware router, it discards held routes and treats the NSF-capable router as a new router joining the network and reestablishing adjacency accordingly.
When the switchover operation is complete, the NSF-capable router notifies its neighbors that it has reconverged and has received all of their topology tables by sending an EOT update packet to the assisting routers. The NSF-capable router then returns to normal operation. The NSF-aware router looks for alternate paths (go active) for any routes that are not refreshed by the NSF-capable (restarting) router. The NSF-aware router returns to normal operation. If all paths are refreshed by the NSF-capable router, the NSF-aware router immediately returns to normal operation.
Non-NSF Aware EIGRP Neighbors
NSF-aware routers are completely compatible with non-NSF aware or non-NSF capable neighbors in an EIGRP network. A non-NSF aware neighbor ignores NSF capabilities and resets the adjacency when they are received.
The NSF-capable router drops any queries that are received while converging to minimize the number of transient routes that are sent to neighbors. The NSF-capable router, however, still acknowledges these queries to prevent these neighbors from resetting adjacency.
Note | An NSF-aware router continues to send queries to an NSF-capable router that is converging after a switchover, effectively extending the time before a stuck-in-active (SIA) condition can occur. |
EIGRP NSF Route-Hold Timers
The route-hold timer is configurable, which allows you to tune network performance and avoid undesired conditions such as “black holing” routes if the switchover operation is lengthy. When the timer expires, the NSF-aware router scans the topology table and discards stale routes, allowing EIGRP peers to find alternate routes instead of waiting during a long switchover operation.
The route-hold timer is configured with the timers graceful-restart purge-time router configuration command. The default time period for the route-hold timer is 240 seconds. The configurable range is from 10 to 300 seconds.
How to Modify and Maintain EIGRP Nonstop Forwarding Awareness
- Adjusting NSF Route-Hold Timers
- Monitoring EIGRP NSF Debug Events and Notifications
- Verifying the Local Configuration of EIGRP NSF Awareness
Adjusting NSF Route-Hold Timers
Perform the following steps to configure NSF route-hold timers on an NSF-aware router.
1.
enable
2.
configure
terminal
3.
router
eigrp
{autonomous-system-number | virtual-instance-name}
4.
address-family
ipv4
[multicast][unicast][vrf vrf-name] autonomous-system autonomous-system-number
5.
timers
graceful-restart
purge-time
seconds
6.
exit
DETAILED STEPS
Troubleshooting Tips
Neighbor adjacencies are maintained during NSF switchover operations. If adjacencies between NSF-capable and NSF-aware neighbors are being reset too often, the route-hold timers may need to be adjusted. The show ip eigrp neighbors detail command can be used to help determine if the route-hold timer value should be set to a longer time period. The time that adjacency is established with specific neighbors is displayed in the output. This time indicates if adjacencies are being maintained or reset and when the last time that specific neighbors were restarted.
Monitoring EIGRP NSF Debug Events and Notifications
Perform the following steps to monitor EIGRP NSF debug events and notifications on an NSF-aware router.
The debug eigrp nsf and debug ip eigrp notifications commands are provided together for example purposes only. You do not have to issue these commands together or in the same session as there are differences in the information that is provided.
Debugging processes are heavy users of CPU resources. Debug commands should not be used in a production network unless you are troubleshooting a problem.
1.
enable
2.
debug
eigrp
nsf
3.
debug
ip
eigrp
notifications
DETAILED STEPS
Command or Action | Purpose | |
---|---|---|
Step 1 |
enable
Example: Router> enable |
Enables higher privilege levels, such as privileged EXEC mode.
|
Step 2 |
debug
eigrp
nsf
Example: Router# debug eigrp nsf |
Displays NSF notifications and information about NSF events in an EIGRP network on the console of the router. |
Step 3 |
debug
ip
eigrp
notifications
Example: Router# debug ip eigrp notifications |
Displays EIGRP events and notifications in the console of the router. The output from this command also includes NSF notifications and information about NSF events. |
Verifying the Local Configuration of EIGRP NSF Awareness
Perform the following steps to verify NSF-awareness configuration on a router that is running EIGRP.
1.
enable
2.
show
ip
protocols
DETAILED STEPS
Command or Action | Purpose | |
---|---|---|
Step 1 |
enable
Example: Router> enable |
Enables higher privilege levels, such as privileged EXEC mode.
|
Step 2 |
show
ip
protocols
Example: Router# show ip protocols |
Displays the parameters and current state of the active routing protocol process. The output of this command can be used to verify EIGRP NSF-awareness. |
Configuration Examples for EIGRP Nonstop Forwarding Awareness
- Example: EIGRP Graceful-Restart Purge-Time Timer Configuration
- Example Monitoring EIGRP NSF Debug Events and Notifications Configuration
- Example Verifying Local Configuration of EIGRP NSF Awareness
Example: EIGRP Graceful-Restart Purge-Time Timer Configuration
The following example shows how to set the graceful-restart purge-time timer to 2 minutes:
Device(config-router)# timers graceful-restart purge-time 120
Example Monitoring EIGRP NSF Debug Events and Notifications Configuration
The following example output shows that an NSF-aware router has received a restart notification. The NSF-aware router waits for EOT to be sent from the restarting (NSF-capable) neighbor.
Router# debug ip eigrp notifications *Oct 4 11:39:18.092:EIGRP:NSF:AS2. Rec RS update from 135.100.10.1, 00:00:00. Wait for EOT. *Oct 4 11:39:18.092:%DUAL-5-NBRCHANGE:IP-EIGRP(0) 2:Neighbor 135.100.10.1 (POS3/0) is up:peer NSF restarted *Sep 23 18:49:07.578: %DUAL-5-NBRCHANGE: EIGRP-IPv4 100: Neighbor 1.1.2.1 (Ethernet1/0) is resync: peer graceful-restart
Example Verifying Local Configuration of EIGRP NSF Awareness
The following is example output from the show ip protocols command. The output from this command can be used to verify the local configuration of EIGRP NSF awareness. The output shows that the router is NSF-aware and that the route-hold timer is set to 240 seconds, which is the default value.
Router# show ip protocols *** IP Routing is NSF aware *** Routing Protocol is “eigrp 101” Outgoing update filter list for all interfaces is not set Incoming update filter list for all interfaces is not set Default networks flagged in outgoing updates Default networks accepted from incoming updates EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0 EIGRP maximum hopcount 100 EIGRP maximum metric variance 1 Redistributing: eigrp 101 EIGRP NSF-aware route hold timer is 240s Automatic network summarization is in effect Maximum path: 4 Routing for Networks: 10.4.9.0/24 Routing Information Sources: Gateway Distance Last Update Distance: internal 90 external 170
Additional References
Related Documents
Related Topic |
Document Title |
---|---|
Cisco IOS commands |
|
CEF commands |
Cisco IOS IP Switching Command Reference |
EIGRP commands |
Cisco IOS IP Routing: EIGRP Command Reference |
NSF with SSO deployment |
Cisco Nonstop Forwarding with Stateful Switchover Deployment Guide |
Standards
Standards |
Title |
---|---|
No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature. |
-- |
MIBs
MIBs |
MIBs Link |
---|---|
No new or modified MIBs are supported by this feature, and support for existing MIBs has not been modified by this feature. |
To locate and download MIBs for selected platforms, Cisco software releases, and feature sets, use Cisco MIB Locator found at the following URL: |
RFCs
RFCs |
Title |
---|---|
RFC 4724 |
Graceful Restart Mechanism for BGP |
Technical Assistance
Description |
Link |
---|---|
The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password. |
Feature Information for EIGRP Nonstop Forwarding Awareness
The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Feature Name |
Releases |
Feature Information |
---|---|---|
EIGRP Nonstop Forwarding (NSF) Awareness |
12.2(15)T 12.2(33)SRE 15.0(1)M 15.0(1)S |
The EIGRP Nonstop Forwarding Awareness feature allows an NSF-aware router running EIGRP to forward packets along routes known to a router performing a switchover operation or in a well-known failure condition. The following commands were introduced or modified: debug eigrp nsf, debug ip eigrp notifications, show ip eigrp neighbors, show ip protocols, timers graceful-restart purge-time, timers nsf route-hold. |