- Configuring OSPF
- OSPFv3 Graceful Restart
- IPv6 Routing: OSPFv3
- OSPF Stub Router Advertisement
- OSPF Update Packet-Pacing Configurable Timers
- OSPF Sham-Link Support for MPLS VPN
- OSPF Support for Multi-VRF on CE Routers
- OSPF Forwarding Address Suppression in Translated Type-5 LSAs
- OSPF Inbound Filtering Using Route Maps with a Distribute List
- OSPFv3 Fast Convergence: LSA and SPF Throttling
- Graceful Shutdown Support for OSPFv3
- OSPFv3 ABR Type 3 LSA Filtering
- OSPFv3 Demand Circuit Ignore
- OSPFv3 External Path Preference Option
- Configuring NSSA for OSPFv3
- Prefix Suppression Support for OSPFv3
- OSPF Retransmissions Limit
- OSPF Mechanism to Exclude Connected IP Prefixes from LSA Advertisements
- OSPFv2 Loop-Free Alternate Fast Reroute
- OSPF Shortest Path First Throttling
- OSPF Support for Fast Hello Packets
- OSPF Incremental SPF
- OSPF Limit on Number of Redistributed Routes
- OSPF Link-State Advertisement Throttling
- OSPF Support for Unlimited Software VRFs per PE Router
- OSPF Area Transit Capability
- OSPF Per-Interface Link-Local Signaling
- OSPF Link-State Database Overload Protection
- OSPF MIB Support of RFC 1850 and Latest Extensions
- OSPF Support for Forwarding Adjacencies over MPLS TE Tunnels
- Configuring OSPF TTL Security Check and OSPF Graceful Shutdown
- Area Command in Interface Mode for OSPFv2
- OSPFv2 Local RIB
- OSPFv3 Address Families
- TTL Security Support for OSPFv3 on IPv6
- OSPF Nonstop Routing
- OSPFv3 NSR
- OSPFv3 MIB
- OSPFv3 IPSec ESP Encryption and Authentication
- IPv6 Routing: OSPFv3 Authentication Support with IPsec
- OSPFv3 VRF-Lite/PE-CE
- Index
- Finding Feature Information
- Prerequisites for OSPF Support for Fast Hello Packets
- Information About OSPF Support for Fast Hello Packets
- How to Configure OSPF Fast Hello Packets
- Configuration Examples for OSPF Support for Fast Hello Packets
- Additional References
- Feature Information for OSPF Support for Fast Hello Packets
OSPF Support for Fast Hello Packets
The OSPF Support for Fast Hello Packets feature provides a way to configure the sending of hello packets in intervals less than 1 second. Such a configuration would result in faster convergence in an Open Shortest Path First (OSPF) network.
- Finding Feature Information
- Prerequisites for OSPF Support for Fast Hello Packets
- Information About OSPF Support for Fast Hello Packets
- How to Configure OSPF Fast Hello Packets
- Configuration Examples for OSPF Support for Fast Hello Packets
- Additional References
- Feature Information for OSPF Support for Fast Hello Packets
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 OSPF Support for Fast Hello Packets
OSPF must be configured in the network already or configured at the same time as the OSPF Support for Fast Hello Packets feature.
Information About OSPF Support for Fast Hello Packets
OSPF Hello Interval and Dead Interval
OSPF hello packets are packets that an OSPF process sends to its OSPF neighbors to maintain connectivity with those neighbors. The hello packets are sent at a configurable interval (in seconds). The defaults are 10 seconds for an Ethernet link and 30 seconds for a non broadcast link. Hello packets include a list of all neighbors for which a hello packet has been received within the dead interval. The dead interval is also a configurable interval (in seconds), and defaults to four times the value of the hello interval. The value of all hello intervals must be the same within a network. Likewise, the value of all dead intervals must be the same within a network.
These two intervals work together to maintain connectivity by indicating that the link is operational. If a router does not receive a hello packet from a neighbor within the dead interval, it will declare that neighbor to be down.
OSPF Fast Hello Packets
OSPF fast hello packets refer to hello packets being sent at intervals of less than 1 second. To understand fast hello packets, you should already understand the relationship between OSPF hello packets and the dead interval. See the section OSPF Hello Interval and Dead Interval.
OSPF fast hello packets are achieved by using the ip ospf dead-interval command. The dead interval is set to 1 second, and the hello-multiplier value is set to the number of hello packets you want sent during that 1 second, thus providing subsecond or "fast" hello packets.
When fast hello packets are configured on the interface, the hello interval advertised in the hello packets that are sent out this interface is set to 0. The hello interval in the hello packets received over this interface is ignored.
The dead interval must be consistent on a segment, whether it is set to 1 second (for fast hello packets) or set to any other value. The hello multiplier need not be the same for the entire segment as long as at least one hello packet is sent within the dead interval.
Benefits of OSPF Fast Hello Packets
The benefit of the OSPF Fast Hello Packets feature is that your OSPF network will experience faster convergence time than it would without fast hello packets. This feature allows you to detect lost neighbors within 1 second. It is especially useful in LAN segments, where neighbor loss might not be detected by the Open System Interconnection (OSI) physical layer and data-link layer.
How to Configure OSPF Fast Hello Packets
Configuring OSPF Fast Hello Packets
1.
enable
2.
configure
terminal
3.
interface
type
number
4.
ip
ospf
dead-interval
minimal
hello-multiplier
multiplier
5.
end
6.
show
ip
ospf
interface
[interface-type
interface-number]
DETAILED STEPS
Examples
The following example output verifies that OSPF Support for Fast Hello Packets is configured. In the line that begins with "Timer intervals configured," the hello interval is 200 milliseconds, the dead interval is 1 second, and the next hello packet is due in 76 milliseconds.
Router# show ip ospf interface ethernet 1/3 Ethernet1/3 is up, line protocol is up Internet Address 172.16.1.2/24, Area 0 Process ID 1, Router ID 172.17.0.2, Network Type BROADCAST, Cost:1 Transmit Delay is 1 sec, State DR, Priority 1 Designated Router (ID) 172.17.0.2, Interface address 172.16.1.2 Backup Designated router (ID) 172.16.0.1, Interface address 172.16.1.1 Timer intervals configured, Hello 200 msec, Dead 1, Wait 1, Retransmit 5 Hello due in 76 msec Index 2/2, flood queue length 0 Next 0x0(0)/0x0(0) Last flood scan length is 2, maximum is 3 Last flood scan time is 0 msec, maximum is 0 msec Neighbor Count is 1, Adjacent neighbor count is 1 Adjacent with neighbor 172.16.0.1 (Backup Designated Router) Suppress hello for 0 neighbor(s)
Configuration Examples for OSPF Support for Fast Hello Packets
Example OSPF Fast Hello Packets
The following example configures OSPF fast hello packets; the dead interval is 1 second and five hello packets are sent every second:
interface ethernet 1 ip ospf dead-interval minimal hello-multiplier 5
Additional References
The following sections provide references related to OSPF Support for Fast Hello Packets.
Related Documents
Related Topic |
Document Title |
---|---|
OSPF commands: complete command syntax, command mode, command history, defaults, usage guidelines, and examples |
Cisco IOS IP Routing: OSPF Command Reference |
Standards
Standards |
Title |
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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 |
---|---|
None |
To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL: |
RFCs
RFCs |
Title |
---|---|
None |
-- |
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 OSPF Support for Fast Hello Packets
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 |
---|---|---|
OSPF Support for Fast Hello Packets |
12.0(23)S 12.2(18)S 12.2(27)SBC 12.2(15)T |
The OSPF Support for Fast Hello Packets feature provides a way to configure the sending of hello packets in intervals less than 1 second. Such a configuration would result in faster convergence in an Open Shortest Path First (OSPF) network. The following command was introduced: ip ospf dead-interval. |