Software Configuration Guide for the Cisco 5900 Embedded Services Routers

Configuring EIGRP in a MANET

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This chapter explains how to configure the Enhanced Interior Gateway Routing Protocol (EIGRP) in a MANET.

This chapter includes the following major sections:

• Understanding The Enhanced Interior Gateway Protocol
• Using EIGRP Cost Metrics for VMI Interfaces
• Understanding VMI Metric to EIGRP Metric Conversion
• Understanding EIGRP Metric Dampening for VMI
• Understanding Neighbor Up/Down Signaling for EIGRP
• Enabling EIGRP for IPv4
• Activating EIGRP IPv4 on a Configured VMI
• Enabling EIGRP for IPv6
• Setting the EIGRP Metric Change-based Dampening for VMI
• Setting the EIGRP Interval-based Metric Dampening for VMI

Understanding The Enhanced Interior Gateway Protocol

The Enhanced Interior Gateway Routing Protocol (EIGRP) integrates the capabilities of link-state protocols into distance vector protocols. EIGRP is distinguished from other routing protocols by the following key capabilities:

• Fast convergence
• Supports variable-length subnet mask
• Supports partial updates
• Supports multiple network layer protocols

A router running EIGRP stores all of its neighbors' routing tables so that the router running EIGRP can quickly adapt to alternate routes. If no appropriate route exists, EIGRP queries its neighbors to discover an alternate route. These queries propagate until an alternate route is found.

EIGRP supports variable-length subnet masks permitting routes to be automatically summarized on a network number boundary. EIGRP can be configured to summarize on any bit boundary at any interface.

EIGRP does not make periodic updates. EIGRP sends partial updates when the route metric changes. Propagation of partial updates is automatically bounded, so only routers needing the information update. EIGRP consumes significantly less bandwidth than the Interior Gateway Routing Protocol (IGRP).

Using EIGRP Cost Metrics for VMI Interfaces

When using EIGRP as the routing protocol, metrics allow EIGRP to respond to routing changes. The link-state metric is advertised as the link cost in the router link advertisement. The reply sent to any routing query always contains the latest metric information. The following exceptions result in an immediate update being sent:

• A down interface
• A down route
• Any change in metrics that result in the router 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)]

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.

Note If K5 = 0, the formula reduces to metric = [K1 * BW + (K2 * BW)/(256 - Load) + K3 * Delay].

Table 11-1 lists the EIGRP vector metrics and their descriptions.

EIGRP monitors metric weights on an interface to allow for the tuning of EIGRP metric calculations and indicate Type of Service (ToS). Table 11-2 lists the K-values and their default.

As shown in Table 11-2 , cost 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 the following formula:

(10^7/minimum BW in kilobits per second)

Note You can change the weights, but these weights must be the same on all the routers.

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

Understanding VMI Metric to EIGRP Metric Conversion

With the VMI interface, the quality of connection to a neighbor varies based on a number of characteristics computed dynamically as a result of layer 2 feedback to layer 3. Table 11-3 lists the metrics and their significance.

Table 11-4 lists these EIGRP vector metric values map to the basic EIGRP interface parameters.

Note Although not explicit in Table 11-4, all variables are converted to the proper units.

Understanding EIGRP Metric Dampening for VMI

Because metric components can change rapidly, the frequency of the changes have an impact on the network. Frequent changes require that prefixes learned though the 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.

The following network changes cause an immediate update:

• A down interface
• A down route
• Any change in a metric that results in the router 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 the 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 with outstanding changes to report are sent out. If a route changes, such that the final metric of the route matches the last updated metric, no update is sent.

Understanding Neighbor Up/Down Signaling for EIGRP

MANETs are highly dynamic environments. Nodes may move in to, or out of, radio range at a fast pace. Each time a node joins or leaves, the network topology must be logically reconstructed by the routers. Routing protocols normally use timer-driven “hello” messages or neighbor time-outs to track topology changes. MANETs reliance on these mechanisms can result in unacceptably slow convergence.

This signaling capability provides faster network convergence by using link-status signals generated by the radio. The radio notifies the router each time a link to another neighbor is established or terminated by the creation and termination of PPPoE sessions. In the router, the EIGRP responds immediately to these signals by expediting the formation of a new adjacency (for a new neighbor) or tearing down an existing adjacency (if a neighbor is lost). For example, if a vehicle drives behind a building and loses its connection, the router immediately senses the loss and establishes a new route to the vehicle through neighbors that are not blocked. This high speed network convergence is essential for minimizing dropped voice calls and disruptions to video sessions.

When VMI with PPPoE is used and a partner node has left or a new one has joined, the radio informs the router immediately of the topology change. Upon receiving the signal, the router immediately declares the change and updates the routing tables.

The signaling capability offers the following benefits:

• Reduces routing delays and prevents applications from timing out
• Enables network-based applications and information to be delivered reliably and quickly over directional radio links
• Provides faster convergence and optimal route selection so that delay-sensitive traffic such as voice and video are not disrupted
• Reduces impact on radio equipment by minimizing the need for internal queuing/buffering
• Provides consistent Quality of Service (QoS) for networks with multiple radios

The messaging allows for flexible rerouting when necessary because of the following factors:

• Noise on the Radio links
• Fading of the Radio links
• Congestion of the Radio links
• Radio link power fade
• Utilization of the Radio

Figure 11-1 illustrates the signaling sequence that occurs when radio links go up and down.

Figure 11-1 Up and Down Signaling Sequence

Enabling EIGRP for IPv4

To create an EIGRP routing process, use the following commands beginning in global configuration mode:

Activating EIGRP IPv4 on a Configured VMI

Perform this task to activate EIGRP IPv4 on a configured VMI.

Enabling EIGRP for IPv6

Perform the following task to enable EIGRP for IPv6 on a specified interface. EIGRP for IPv6 is directly configured on the interfaces over which it runs, which allows EIGRP for IPv6 to be configured without the use of a global IPv6 address.

Setting the EIGRP Metric Change-based Dampening for VMI

Perform the following tasks to set the change-based dampening interval for VMI:

This configuration assumes that a virtual template and appropriate PPPoE configurations have already been completed. Refer to the Cisco IOS IP Mobility Configuration Guide for VMI configuration details.

This configuration sets the threshold to 50 percent tolerance routing updates involving VMIs and peers.

Setting the EIGRP Interval-based Metric Dampening for VMI

Perform this task to set an interval-based dampening interval for VMI interfaces.

This configuration assumes that a virtual template and appropriate PPPoE configurations have already been completed. Refer to the Cisco IOS IP Mobility Configuration Guide for VMI configuration details.

This configuration sets the interval to 30 seconds at which updates occur for topology changes that affect VMI interfaces and peers: