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EIGRP nonstop forwarding (NSF) capabilities are exchanged by EIGRP peers in hello packets. NSF works with the SSO feature in Cisco software to minimize the amount of time that a network is unavailable to its users following a switchover. The main objective of NSF is to continue forwarding IP packets following a Route Processor (RP) switchover.
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. |
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 at the end of this module.
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.
Note |
Distributed platforms that run a supporting version of Cisco software can support full NSF capabilities. These devices can perform a restart operation and can support other NSF capable peers. |
Information About EIGRP Nonstop Forwarding
Note |
In the following content, 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. |
NSF works with the SSO feature in Cisco software to minimize the amount of time a network is unavailable to its users following a switchover. The main objective of NSF is to continue forwarding IP packets following an 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. NSF helps to suppress routing flaps in SSO-enabled devices, thus reducing network instability.
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 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 NSF operation.
The NSF feature provides the following benefits:
NSF always runs together with SSO. 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 during an RP switchover. For some HA-aware protocols and applications, state information is synchronized from the active to the standby processor.
Cisco NSF is supported by the EIGRP protocol for routing and by CEF for forwarding. EIGRP 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.
EIGRP nonstop forwarding (NSF) capabilities are exchanged by EIGRP peers in hello packets. The NSF-capable device notifies its neighbors that an NSF restart operation has started by setting the restart (RS) bit in a hello packet. When an NSF-aware device receives notification from an NSF-capable neighbor that an NSF-restart operation is in progress, the NSF-capable and NSF-aware devices immediately exchange their topology tables. The NSF-aware device sends an end-of-table (EOT) update packet when the transmission of its topology table is complete. The NSF-aware device then performs the following actions to assist the NSF-capable device:
When the switchover operation is complete, the NSF-capable device notifies its neighbors that it has reconverged and has received all of their topology tables by sending an EOT update packet to the assisting devices. The NSF-capable device then returns to normal operation. The NSF-aware device will look for alternate paths (go active) for any routes that are not refreshed by the NSF-capable (restarting device). The NSF-aware device will then return to normal operation. If all paths are refreshed by the NSF-capable device, the NSF-aware device will immediately return to normal operation.
NSF-aware devices are completely compatible with non-NSF-aware or non-NSF-capable neighbors in an EIGRP network. A non-NSF-aware neighbor will ignore NSF capabilities and reset adjacencies and otherwise maintain the peering sessions normally.
How to Configure EIGRP Nonstop Forwarding
Repeat this task on each peer device.
1. enable
2. configure terminal
3. router eigrp as-number
4. nsf
5. timers nsf converge seconds
6. timers nsf signal seconds
7. timers graceful-restart purge-time seconds
8. end
9. show ip protocols
Use the following commands in any order to troubleshoot issues with nonstop forwarding using the EIGRP protocol.
1. enable
2. debug eigrp nsf
3. debug ip eigrp notifications
4. show cef nsf
5. show cef state
6. show ip cef
7. show ip eigrp neighbors detail
Configuration Examples for EIGRP Nonstop Forwarding
The following sample output shows that EIGRP NSF support is present in the installed software image.
Device# show ip protocols Routing Protocol is "eigrp 100" 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 100 EIGRP NSF-aware route hold timer is 240s EIGRP NSF enabled NSF signal timer is 20s NSF converge timer is 120s 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
Related Topic |
Document Title |
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Cisco IOS commands |
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EIGRP commands |
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EIGRP FAQ |
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EIGRP L2/L3 API and Tunable Metric for Mobile Adhoc Networks feature |
“Mobile Ad Hoc Networks for Router-to-Radio Communications” module of the IP Mobility Configuration Guide |
EIGRP Technology Support |
|
EIGRP Technology White Papers |
|
IPv6 Routing EIGRP Support |
EIGRP Configuration Guide |
Protocol-independent features that work with EIGRP |
IP Routing: Protocol-Independent Configuration Guide |
Service Advertisement Framework |
Service Advertisement Framework Configuration Guide |
Service Advertisement Framework commands |
Standard/RFC |
Title |
---|---|
FIPS PUB 180-2 |
SECURE HASH STANDARD (SHS) |
RFC 1321 |
The MD5 Message-Digest Algorithm |
RFC 2104 |
HMAC: Keyed-Hashing for Message Authentication |
Description |
Link |
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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. |
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 |
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NSF – EIGRP |
Cisco IOS XE Release 3.2SE |
EIGRP nonstop forwarding (NSF) capabilities are exchanged by EIGRP peers in hello packets. NSF works with the SSO feature in Cisco software to minimize the amount of time that a network is unavailable to its users following a switchover. The main objective of NSF is to continue forwarding IP packets following a Route Processor (RP) switchover. The following commands were introduced or modified: debug ip eigrp notifications, nsf (EIGRP), router eigrp, and show ip eigrp neighbors. |