-
IP Mobility: Mobile Networks Configuration Guide, Cisco IOS Release 15M&T
-
Cisco Mobile Networks
-
Cisco Mobile Networks Asymmetric Link
-
Cisco Mobile Networks Static Collocated Care-of Address
-
Cisco Mobile Networks Priority HA Assignment
-
Cisco Mobile Networks Tunnel Templates for Multicast
-
Mobile Networks Dynamic Collocated Care-of Address
-
Mobile Networks Deployment MIB
-
Mobile IP - Foreign Agent Local Routing to Mobile Networks
-
Mobile IP - Generic Routing Encapsulation for Cisco Mobile Networks
-
Mobile IP Support for RFC 3519 NAT Traversal on the Mobile Router
-
Mobile IP Policy and Application-Based Routing for MR Multipath
-
Mobile Router DHCP Support for Dynamic CCoA and Foreign Agent Processing
-
MANET Enhancements to PPPoE for Router-to-Radio Links
-
OSPFv3 Extensions for Mobile Ad Hoc Networks
-
IP Multiplexing
-
MANET Enhancements to PPPoE for Router-to-Radio Links
-
EIGRP Dynamic Metric Calculations
-
Multicast for Virtual Multipoint Interfaces
-
OSPFv3 Dynamic Interface Cost Support
-
VMI QoS
-
Feedback
Contents
- EIGRP Dynamic Metric Calculations
- Finding Feature Information
- Prerequisites for EIGRP Dynamic Metric Calculations
- Information About EIGRP Dynamic Metric Calculations
- Link-Quality Metrics Reporting for EIGRP
- EIGRP Cost Metrics for VMIs
- VMI Metric to EIGRP Metric Conversion
- EIGRP Metric Dampening for VMIs
- How to Configure EIGRP Dynamic Metric Calculations
- Setting the EIGRP Change-based Dampening Interval Using Classic-Style Configuration
- Setting the EIGRP Change-based Dampening Interval Using Named-Style Configuration
- Setting the EIGRP Interval-based Dampening Interval Using Classic-Style Configuration
- Setting the EIGRP Interval-based Dampening Interval Using Named-Style Configuration
- Configuration Examples for EIGRP Dynamic Metric Calculations
- Example: EIGRP Change-based Dampening for VMIs
- Example: EIGRP Interval-based Dampening for VMIs
- Additional References
- Feature Information for EIGRP Dynamic Metric Calculations
EIGRP Dynamic Metric Calculations
The EIGRP Dynamic Metric Calculations features enables the Enhanced Interior Gateway Routing Protocol (EIGRP) to use dynamic raw radio-link characteristics (current and maximum bandwidth, latency, and resources) to compute a composite EIGRP metric. A tunable hysteresis mechanism helps to avoid churn in the network as a result of the change in the link characteristics. In addition to the link characteristics, the L2/L3 API provides an indication when a new adjacency is discovered, or an existing unreachable adjacency is again reachable. When the Interior Gateway Routing Protocol (IGRP) receives the adjacency signals, it responds with an immediate Hello out the specified interface to expedite the discovery of the EIGRP peer.
- Finding Feature Information
- Prerequisites for EIGRP Dynamic Metric Calculations
- Information About EIGRP Dynamic Metric Calculations
- How to Configure EIGRP Dynamic Metric Calculations
- Configuration Examples for EIGRP Dynamic Metric Calculations
- Additional References
- Feature Information for EIGRP Dynamic Metric Calculations
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 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.
Information About EIGRP Dynamic Metric Calculations
Link-Quality Metrics Reporting for EIGRP
The quality of a radio link has a direct impact on the throughput that can be achieved by device-to-device traffic. The PPP over Ethernet (PPPoE) provides a process by which a device can request, or a radio can report, link-quality metric information. With the Cisco Enhanced Interior Gateway Routing Protocol (EIGRP) implementation, the route cost to a neighbor is dynamically updated based on metrics reported by the radio, thus allowing the best route to be chosen within a given set of radio links and reducing the effect of frequent routing changes.
The routing protocols receive raw radio-link data and compute a composite quality metric for each link In computing these metrics, you should consider these factors:
- Maximum data rate--the theoretical maximum data rate of the radio link, in scaled bits per second
- Current data rate--the current data rate achieved on the link, in scaled bits per second
- Resources--a percentage (0 to 100) that can represent the remaining amount of a resource (such as battery power)
- Latency--the transmission delay packets encounter, in milliseconds
- Relative link quality--a numeric value (0 to 100) representing relative quality, with 100 being the highest quality
You can weight metrics during the configuration process to emphasize or deemphasize particular characteristics. For example, if throughput is a particular concern, you can weight the throughput metric so that it is factored more heavily into the composite route cost. Similarly, a metric of no concern can be omitted from the composite calculation
Link metrics can change rapidly, often by very small degrees, which can result in a flood of meaningless routing updates. In a worst-case scenario, the network could churn almost continuously as it struggles to react to minor variations in link quality. To alleviate this concern, Cisco provides a tunable dampening mechanism that allows you to configure threshold values. Any metric change that falls below the threshold is ignored. The quality of a connection to a neighbor varies, based on various characteristics of the interface when EIGRP is used as the routing protocol. The routing protocol receives dynamic raw radio-link characteristics and computes a composite metric that is used to reduce the effect of frequent routing changes.
By using the tunable hysteresis mechanism, you can adjust the threshold to the routing changes that occur when the device receives a signal that a new peer has been discovered or that an existing peer is unreachable. The tunable metric is weighted and is adjusted dynamically to account for these characteristics:
You can deconfigure individual weights, and you can clear all weights so that the cost returns to the default value for the interface type. Based on the routing changes that occur, you can determine the cost by applying these metrics.
EIGRP Cost Metrics for VMIs
When the Enhanced Interior Gateway Routing Protocol (EIGRP) is used as the routing protocol, metrics allow EIGRP to respond to routing changes. The link-state metric is advertised as the link cost in the device link advertisement. The reply sent to any routing query always contains the latest metric information. The exceptions that result in an immediate update being sent are:
- A down interface
- A down route
- Any change in a metric that results in the device selecting a new next hop
EIGRP receives dynamic raw radio-link characteristics and computes a composite EIGRP metric based on a proprietary formula. To avoid churn in the network as a result of the change in the link characteristics, EIGRP uses a tunable dampening mechanism.
EIGRP uses the metric weights along with a set of vector metrics to compute the composite metric for local routing information base (RIB) installation and route selections. The EIGRP composite metric is calculated using the formula:
metric = [K1 * BW + (K2 * BW) / (256 - Load) + K3 * Delay] * [K5 / (Reliability + K4)]
If K5 = 0, the formula reduces to metric = [K1 * BW + (K2 * BW)/(256 - Load) + K3 * Delay]
 Note | Use K values only after careful planning. Mismatched K values prevent a neighbor relationship from being built, which can cause your network to fail to converge. |
The table below lists the EIGRP vector metrics and their descriptions.
| Table 1 | EIGRP Vector Metrics |
|
Vector Metric |
Description |
|---|---|
|
BW |
Minimum bandwidth of the route in kb/s. It can be 0 or any positive integer. |
|
Delay |
Route delay in tens of microseconds. It can be 0 or any positive number that is a multiple of 39.1 nanoseconds. |
|
Reliability |
Likelihood of successful packet transmission expressed as a number from 0 to 255. The value 255 means 100 percent reliability; 0 means no reliability. |
|
Load |
Effective load of the route expressed as a number from 0 to 255 (255 is 100 percent loading). |
|
MTU |
Minimum maximum transmission unit (MTU) size of the route in bytes. It can be 0 or any positive integer. |
EIGRP monitors metric weights on an interface to allow for the tuning of EIGRP metric calculations and indicate the type of service (ToS). The table below lists the K-values and their default.
Most configurations use the first two metrics--delay and bandwidth. The default formula of (BW + Delay) is the EIGRP metric. The bandwidth for the formula is scaled and inverted by this formula:
(10^7/minimum BW in kilobits per second)
You can change the weights, but these weights must be the same on all the devices.
For example, look at an EIGRP link where the bandwidth to a particular destination is 128k and the Relative Link Quality (RLQ) is 50 percent.
BW = (256 * 10000000) / 128 = 20000000
Delay = (((10000000000 / 128) * 100) / (50 * 1000)) * 256 = (40000000 / 10) = 4000000
Using the cut-down formula, the EIGRP metric calculation would simplify to 256*(BW + Delay), resulting in the following value:
Metric = (BW + Delay) = 20000000 + 4000000 = 240000000
VMI Metric to EIGRP Metric Conversion
The quality of connection to a virtual multipoint interface (VMI) neighbor varies based on various characteristics computed dynamically based on the feedback from Layer 2 to Layer 3. The table below lists the Enhanced Interior Gateway Routing Protocol (EIGRP) metrics and their significance.
| Table 3 | EIGRP MANET Metrics for VMI Interfaces |
|
Metric |
Significance |
|
|---|---|---|
|
Current data rate |
uint64_t |
The current data rate reported from the radio. EIGRP converts the value into kilobits per second. |
|
Max data rate |
uint64_t |
The maximum data rate reported from the radio. EIGRP converts the value into kilobits per second. |
|
Latency |
unsigned int |
The latency computed and reported by the radio in milliseconds. |
|
Resources |
unsigned int |
The resources computed by the radio. A representation of resources, such as battery power, ranges from 0 to 100. If a radio does not report dynamic resources, the value is always 100. |
|
Relative link quality |
unsigned int |
An opaque number that ranges from 0 to 100 is computed by the radio, representing radio's view of link quality. 0 represents the worst possible link, 100 represents the best possible link. |
|
Link-load |
unsigned int |
An opaque number that ranges from 0 to 100 is computed by VMI, representing the load on the Ethernet link. 0 represents an idle Ethernet link, 100 represents a fully loaded Ethernet link. Note that this is not associated with the radio link. |
The table below shows how these EIGRP vector metric values map to the basic EIGRP interface parameters.
| Table 4 | Mapping of VMI Metric Values to EIGRP Vector Metrics Values |
|
VMI Metric |
EIGRP Metric |
Mapping |
|---|---|---|
|
Current data rate |
Bandwidth |
Calculated: bandwidth = (256 * 10000000) / (current data rate / 1000) |
|
Relative link quality resources |
Reliability |
Calculated: reliability = (255 * (relative link quality) / 100)) * (resources / 100) |
|
Current data rate Relative link quality |
Delay |
Calculated: delay = 256 * (1E10 / (current data rate / 1000)) * ((100 / relative link quality) / 1000) / 10 |
|
Load |
Load |
Calculated: load = ((255 * link-load) / 100) |
EIGRP Metric Dampening for VMIs
Rapid changes in metric components can affect the network by requiring that prefixes learned though the virtual multipoint interface (VMI) be updated and sent to all adjacencies. This update can result in further updates and, in a worst-case scenario, cause network-wide churn. To prevent such effects, metrics can be dampened, or thresholds set, so that any change that does not exceed the dampening threshold is ignored.
Network changes that cause an immediate update include
- A down interface
- A down route
- Any change in a metric that results in the device selecting a new next hop
Dampening the metric changes can be configured based on change or time intervals.
If the dampening method is change-based, changes in routes learned though a specific interface, or in the metrics for a specific interface, are not advertised to adjacencies until the computed metric changes from the last advertised value significantly enough to cause an update to be sent.
If this dampening method is interval-based, changes in routes learned though a specific interface, or in the metrics for a specific interface, are not advertised to adjacencies until the specified interval is met, unless the change results in a new route path selection.
When the timer expires, any routes that have outstanding changes to report are sent. If a route changes, such that the final metric of the route matches the last updated metric, no update is sent.
How to Configure EIGRP Dynamic Metric Calculations
- Setting the EIGRP Change-based Dampening Interval Using Classic-Style Configuration
- Setting the EIGRP Change-based Dampening Interval Using Named-Style Configuration
- Setting the EIGRP Interval-based Dampening Interval Using Classic-Style Configuration
- Setting the EIGRP Interval-based Dampening Interval Using Named-Style Configuration
Setting the EIGRP Change-based Dampening Interval Using Classic-Style Configuration
Perform this optional task to set the Enhanced Interior Gateway Routing Protocol (EIGRP) change-based dampening interval for virtual multipoint interfaces (VMIs) using classic-style configuration. Configuring the router eigrp autonomous-system-number command creates an EIGRP configuration referred to as autonomous system (AS) configuration. An EIGRP AS configuration creates an EIGRP routing instance that can be used for tagging routing information.
You can configure this feature with either an IPv4 or an IPv6 address, or you can use both. If you are using both IPv4 and IPv6, complete the entire configuration.
This configuration sets the threshold to 50 percent tolerance for routing updates involving VMIs and peers.
DETAILED STEPS
Setting the EIGRP Change-based Dampening Interval Using Named-Style Configuration
Perform this optional task to set the Enhanced Interior Gateway Routing Protocol (EIGRP) change-based dampening interval for virtual multipoint interfaces (VMIs) using named-style configuration. Configuring the router eigrp virtual-instance-name command creates an EIGRP configuration referred to as an EIGRP named configuration. An EIGRP named configuration does not create an EIGRP routing instance by itself. EIGRP named configuration is a base configuration that is required to define address-family configurations under it that are used for routing.
You can configure this feature with either an IPv4 or an IPv6 address, or you can use both. If you are using both IPv4 and IPv6, then complete the entire configuration.
This configuration sets the threshold to 50 percent tolerance for routing updates involving VMIs and peers.
DETAILED STEPS
Setting the EIGRP Interval-based Dampening Interval Using Classic-Style Configuration
Perform this optional task to set an Enhanced Interior Gateway Routing Protocol (EIGRP) interval-based dampening interval for virtual multipoint interfaces (VMIs) using classic-style configuration. Configuring the router eigrp autonomous-system-number command creates an EIGRP configuration referred to as autonomous system (AS) configuration. An EIGRP AS configuration creates an EIGRP routing instance that can be used for tagging routing information.
This configuration sets the interval to 30 seconds at which updates occur for topology changes that affect VMIs and peers.
DETAILED STEPS
Setting the EIGRP Interval-based Dampening Interval Using Named-Style Configuration
Perform this optional task to set an Enhanced Interior Gateway Routing Protocol (EIGRP) interval-based dampening interval for virtual multipoint interfaces (VMIs) using named-style configuration. Configuring the router eigrp eigrp virtual-instance-name command creates an EIGRP configuration referred to as an EIGRP named configuration. An EIGRP named configuration does not create an EIGRP routing instance by itself. EIGRP named configuration is a base configuration that is required to define address-family configurations under it that are used for routing.
This configuration sets the interval to 30 seconds at which updates occur for topology changes that affect VMIs and peers.
DETAILED STEPS
Configuration Examples for EIGRP Dynamic Metric Calculations
Example: EIGRP Change-based Dampening for VMIs
The following example configures the Enhanced Interior Gateway Routing Protocol (EIGRP) address-family Ethernet interface 0/0 to limit the metric change frequency to no more than one change in a 45-second interval:
Device(config)# router eigrp virtual-name Device(config-router)# address-family ipv4 autonomous-system 5400 Device(config-router-af)# af-interface ethernet 0/0 Device(config-router-af-interface)# dampening-interval 45
Example: EIGRP Interval-based Dampening for VMIs
The following example configures the Enhanced Interior Gateway Routing Protocol (EIGRP) address-family Ethernet interface 0/0 to limit the metric change frequency to no more than one change in a 45-second interval:
Device(config)# router eigrp virtual-name Device(config-router)# address-family ipv4 autonomous-system 5400 Device(config-router-af)# af-interface ethernet 0/0
Additional References
Related Documents
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 Dynamic Metric Calculations
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.
| Table 5 | Feature Information for EIGRP Dynamic Metric Calculations |
| Feature Name | Releases | Feature Information |
|---|---|---|
|
EIGRP Dynamic Metric Calculations |
12.4(15)XF 12.4(15)T 15.0(1)M |
The EIGRP Dynamic Metric Calculations features enables the Enhanced Interior Gateway Routing Protocol (EIGRP) to use dynamic raw radio-link characteristics (current and maximum bandwidth, latency, and resources) to compute a composite EIGRP metric. A tunable hysteresis mechanism helps to avoid churn in the network as a result of the change in the link characteristics. In addition to the link characteristics, the L2/L3 API provides an indication when a new adjacency is discovered, or an existing unreachable adjacency is again reachable. When the Interior Gateway Routing Protocol (IGRP) receives the adjacency signals, it responds with an immediate Hello out the specified interface to expedite the discovery of the EIGRP peer. The following commands were introduced or modified: dampening-change, dampening-interval, debug eigrp notifications, debug vmi. |
Cisco and the Cisco logo are trademarks or registered trademarks of Cisco and/or its affiliates in the U.S. and other countries. To view a list of Cisco trademarks, go to this URL: 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. (1110R)
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.