Table Of Contents
Mobile Ad Hoc Networks for Router-to-Radio Communications
Prerequisites for Mobile Ad Hoc Networks for Router-to-Radio Communications
Restrictions for Mobile Ad Hoc Networks for Router-to-Radio Communications
Information About Mobile Ad Hoc Networks for Router-to-Radio Communications
MANETs for Router-to-Radio Communications
PPPoE Interfaces for Mobile Radio Communications
Link Quality Metrics Reporting for OSPFv3 and EIGRP with VMI Interfaces
Neighbor Up/Down Signaling for OSFPv3 and EIGRP
PPPoE Credit-based Flow Control
How to Configure Router-to-Radio Links Using VMI PPPoE
Implementing the VMI Infrastructure Using PPPoE
Implementing the VMI and Configuring the Routing Protocol
Configuration Examples for VMI PPPoE
Basic VMI PPPoE Configuration with EIGRP IPv4: Example
Basic VMI PPPoE Configuration Using EIGRP for IPv6: Example
VMI PPPoE Configuration Using EIGRP for IPv4 and IPv6: Example
VMI PPPoE Configuration for OSPFv3: Example
VMI PPPoE Configuration Using Multiple Virtual Templates: Example
Marking and Queuing Packets over VMI: Example
Feature Information About the Mobile Ad Hoc Networks for Router-to-Radio Communications
Mobile Ad Hoc Networks for Router-to-Radio Communications
First Published: May 17, 2007
Last Updated: May 17, 2007Mobile Ad Hoc Networks (MANET) for router-to-radio communications address the challenges faced when merging IP routing and mobile radio communications in ad hoc networking applications. the Cisco solution for MANETs provides capabilities that enable
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Optimal route selection based on Layer 2 feedback from the radio network
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Through the router-to-radio link, the radio can inform the router immediately when a node joins or leaves, and this enables the router to recognize topology changes more quickly than if it had to rely on timers. Without this link-status notification from the radio, the router would likely time out while waiting for traffic. The link-status notification from the radio enables the router to respond faster to network topology changes. Metric information regarding the quality of a link is passed between the router and radio, enabling the router to more intelligently decide on which link to use.
With the link-status signaling provided by the router-to-radio link, applications such voice and video work better because outages caused by topology changes are reduced or eliminated. Sessions are more stable and remain active longer.
Key features of Cisco's mobile ad hoc networks for router-to-radio communications include the following:
Link Quality Metrics Reporting
The PPPoE protocol has been extended to enable a router or radio to query or report link-quality metric information. Cisco routers have been enhanced so that OSPFv3 or EIGRP routing protocols can factor link quality metrics into route cost calculations.
Neighbor Up or Down Signaling
Neighbor up or down signaling enables Cisco routers to use link establishment or termination signals from the radio to update routing topology.
PPPoE Credit-based Flow Control
This extension to the PPPoE protocol allows a receiver to control the rate at which a sender can transmit data for each PPPoE session, so that the need for queuing in the radio is minimized.
Virtual Multipoint Interface (VMI)
This Cisco router enhancement maps multiple PPPoE sessions (each representing a point-to-point neighbor connection) into a single broadcast-capable, multi-access interface.
Finding Feature Information in This Module
Your Cisco IOS software release may not support all of the features documented in this module. To reach links to specific feature documentation in this module and to see a list of the releases in which each feature is supported, use the " "Command Reference" section.
Finding Support Information for Platforms and Cisco IOS and Catalyst OS Software Images
Use Cisco Feature Navigator to find information about platform support and Cisco IOS and Catalyst OS software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
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Prerequisites for Mobile Ad Hoc Networks for Router-to-Radio Communications
The features described in this document require one of the following router platforms:
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To use the PPPoE and virtual multipoint interface (VMI) features described in this document, a radio device that implements the PPPoE functionality enhancements described in the draft RFC 2516 is required. Users can optionally implement draft-bberry-pppoe-credit-06.txt for PPP Over Ethernet (PPPoE) Extensions for Credit Flow and Link Metrics, but this draft must be implemented if you plan to use VMI features.
Restrictions for Mobile Ad Hoc Networks for Router-to-Radio Communications
VMI on Routed Ports
VMIs can be configured only on routed ports. VMIs are not supported on VLAN or switched ports.
Quality of Service
Of the Quality of Service (QoS) queueing features available from Cisco, only class-based Weighted Fair Queueing (WFQ) is supported on VMIs. The VMI can identify Differentiated Services Code Point (DSCP) values, and perform network-based application recognition (NBAR), but no policing or policy mapping occurs on those matches.
Information About Mobile Ad Hoc Networks for Router-to-Radio Communications
This section describes VMI PPPoE. The following sections are included:
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Benefits of Router-to-Radio Links Using Virtual Multipoint Interfaces with PPPoE in Cisco IOS Software
As the global leader in mission-critical networking and IP communications, Cisco is uniquely positioned to deliver reliable and efficient converged voice, video, and data solutions to organizations around the world. Benefits of this technology include the following:
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MANETs for Router-to-Radio Communications
Mobile Ad Hoc Networks (MANETs) enable users deployed in areas with no fixed communications infrastructure to access critical voice, video, and data services. Soldiers in the field can employ unified communications, multimedia applications, and real-time information dissemination to improve situational awareness and respond quickly to changing battlefield conditions. Disaster managers can use video conferences, database access, and collaborative tools to coordinate multi-agency responses within an Incident Command System (ICS) framework. For event planners and trade show managers, MANETs represent a cost-effective way to accommodate mobile end users on a short term basis. MANETs set the stage for more timely information sharing and faster, more effective decision-making.
In MANET environments, highly mobile nodes communicate with each other across bandwidth-constrained radio links. An individual node includes both a radio and a network router, with the two devices interconnected over an Ethernet. Since these nodes can rapidly join or leave the network, MANET routing topologies are highly dynamic. Fast convergence in a MANET becomes a challenge because the state of a node can change well before the event is detected by the normal timing mechanisms of the routing protocol.
Radio link quality in a MANET can vary dramatically because it can be affected by a variety of factors such as noise, fading, interference, and power fluctuation. As a result, avoiding congestion and determining optimal routing paths also pose significant challenges for the router network. Finally, directional radios that operate on a narrow beam tend to model the network as a series of physical point-to-point connections with neighbor nodes. This point-to-point model does not translate gracefully to multi-hop, multipoint router environments, as it increases the size of each router's topology database and reduces routing efficiency.
Effective networking in a MANET environment therefore requires mechanisms by which
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PPPoE Interfaces for Mobile Radio Communications
The Cisco MANET solution employs PPP-over-Ethernet (PPPoE) sessions to enable intra-nodal communications between a router and its partner radio. Each radio initiates the PPPoE session as soon as the radio establishes a radio link to another radio. After the PPPoE sessions are active, a PPP session is established end-to-end (router-to-router); This is duplicated each time a radio establishes a new radio link. The Virtual Multipoint Interface (VMI) on the router aggregates multiple PPPoE sessions and multiplexes these to look like a single interface to the routing processes. This interface collects the series of PPP/PPPoE connections. Underneath the VMI interface there are virtual access interfaces that are associated with each of the PPP/PPPoE connections.
A PPPoE session is established between a router and a radio on behalf of every other router/radio neighbor located in the MANET. These Layer 2 sessions are the means by which radio network status gets reported to the Layer 3 processes in the router. Figure 1 illustrates the PPPoE session exchange between mobile routers and directional radios in a MANET network.
Figure 1 PPPoE Session Exchange Between Mobile Routers and Directional Radios
This capability assumes that a PPPoE-equipped radio connects to a router using Ethernet. The router always considers the Ethernet link to be up. If the radio side of the link goes down, the router will wait until a routing update time-out has occurred to declare the route down and then update the routing table. Figure 2 illustrates a simple router-to-radio link topology.
Figure 2 Router-to-Radio Link
Routing protocols used for VMI PPPoE are EIGRP (IPv4, IPv6) and OSPFv3 (IPv6).
Virtual Multipoint Interface
The VMI interface provides services that map outgoing packets to the appropriate PPPoE sessions based on the next-hop forwarding address for that packet. The VMI interface also provides a broadcast service that emulates a set of point-to-point connections as a point-to-multipoint interface with broadcast ability. When a packet with a multicast address is forwarded through the VMI interface, VMI replicates the packet and unicasts it to each of its neighbors.
Directional radios are frequently used in applications that require greater bandwidth, increased power-to-transmission range, or reduced probability of detection. These radios operate in a point-to-point mode, and generally have no broadcast capability. On the other hand, the routing processes in Cisco's MANET solution operate most efficiently when viewing the network link as point-to-multipoint, with broadcast capability. For the router, modeling the MANET as a collection of point-to-point nodes would have a dramatic impact on the size of its internal database.
The Virtual Multipoint Interface (VMI) within the router aggregates all of the per-neighbor PPPoE sessions from the Radio Ethernet connection. The VMI maps the sessions to appear to Layer 3 routing protocols and applications as a single point-to-multipoint, multi-access, broadcast-capable network. However, the VMI preserves the integrity of the PPPoE sessions on the radio side, so that each point-to-point connection can have its own Quality of Service (QoS) queue.
The VMI also relays the link quality metric and neighbor up/down signaling from the radio to the routing protocols. Currently, VMI signals are used by EIGRP (for IPv4 and IPv6 neighbors) and OSPFv3 (for IPv6 neighbors).
Link Quality Metrics Reporting for OSPFv3 and EIGRP with VMI Interfaces
The quality of a radio link has a direct impact on the throughput that can be achieved by router-router traffic. The PPPoE protocol has been extended to provide a process by which a router can request, or a radio can report, link quality metric information. Cisco's OSFPv3 and EIGRP implementations have been enhanced so that 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.
The routing protocols receive raw radio link data, and compute a composite quality metric for each link. In computing these metrics, the following factors may be considered:
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Metrics can be weighted during the configuration process to emphasize or de-emphasize particular characteristics. For example, if throughput is a particular concern, the current data rate metric could be weighted so that it is factored more heavily into the composite metric. Similarly, a metric that is of no concern can be omitted from the composite calculation.
Link metrics can change rapidly, often by very small degrees, which could result in a flood of meaningless routing updates. In a worst case scenario, the network would be churning almost continuously as it struggled to react to minor variations in link quality. To alleviate this concern, Cisco provides a tunable dampening mechanism that allows the user 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 OSPF or 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.
A tunable hysteresis mechanism allows users to adjust the threshold to the routing changes that occur when the router 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 the following characteristics:
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Individual weights can be deconfigured and all weights can be cleared so that the cost is set back to the default value for the interface type. Based on the routing changes that occur, cost can be determined by the application of these metrics. The following sections provide more details about OSPF and EIGRP metrics:
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OSPF Cost Calculation
Because cost components can change rapidly, it might be necessary to dampen the volume of changes to reduce network-wide churn. The recommended values for S2, S3, and S4 are based on network simulations that may reduce the rate of network changes. The recommended value for S1 is zero to eliminate this variable from the route cost calculation.
The overall link cost is computed using the following formula:
Table 1 defines the symbols used in the OSPF cost calculation.
While each network might have unique characteristics that require different settings to optimize actual network performance, these are recommended values intended as a starting point for optimizing a OSPFv3 network. Table 2 lists the recommended value settings for OSPF cost metrics.
Using this formula, the default path costs were calculated as noted in the following list. If these values do not suit your network, you can use your own method of calculating path costs.
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To illustrate these settings, the following example shows how OSPF cost metrics might be defined for a VMI interface:
interface vmi1ipv6 ospf cost dynamic weight throughput 0ipv6 ospf cost dynamic weight resources 29ipv6 ospf cost dynamic weight latency 29ipv6 ospf cost dynamic weight L2-factor 29EIGRP Cost Metrics
When 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 router link advertisement.The reply sent to any routing query will always contain the latest metric information. Exceptions which will result in immediate update being sent:
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EIGRP uses the metric weights along with a set of vector metrics to compute the composite metric for local RIB installation and route selections. The EIGRP composite metric is calculated using the formula:
EIGRP Metric = 256*((K1*Bw) + (K2*Bw)/(256-Load) + (K3*Delay)*(K5/(Reliability + K4)))
Table 3 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 4 lists the K-values and their default.
Most configurations use the first two metrics -delay and bandwidth, with bandwidth taking precedence. The default formula of 256*(BW +Delay) is the EIGRP metric.
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For example, look at an IGRP link whose bandwidth to a particular destination is 128k and the delay is 84000 microseconds.
Using the cut-down formula, the EIGRP metric calculation would simplify to 256*(BW + Delay), resulting in the following value:
Metric = 256*(10^7/128 + 84000/10)= 256*86525 = 22150400
VMI Metric to EIGRP Metric Conversion
The quality of connection to a VMI neighbor will vary based on various characteristics computed dynamically based on the feedback from L2 to L3. Table 5 lists the EIGRP metrics and their significance.
These EIGRP metric values map to the basic EIGRP interface parameters as indicated in Table 6
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Dynamic Cost Metric for Interfaces
The dynamic cost metric used for interfaces is computed based on the Layer 2 (L2) feedback to Layer 3 (L3). The dynamic cost is calculated using the following formula:
L2L3API
Where the metric calculations are
S1 = ipv6 ospf dynamic weight throughput
S2 = ipv6 ospf dynamic weight resources
S3 = ipv6 ospf dynamic weight latency
S4 = ipv6 ospf dynamic weight L2 factor
OC = standard cost of a non-VMI routeThroughput = (current-data-rate)/(maximum-data-rate)
Router-dynamic cost= OC + (S1) + (S2) + (S3) + (S4)
For a dynamic cost to have the same cost as a default cost, all parameters must equal zero.
Each Layer 2 feedback can contribute a cost in the range of 0 to 65535. To tune down this cost range, use the optional weight keyword in conjunction with the throughput, resources, latency, or L2-factor keyword. Each of these weights has a default value of 100% and can be configured in the range from 0 to 100. When 0 is configured for a specific weight, that weight does not contribute to the Open Shortest Path First (OSPF) cost.
Because cost components can change rapidly, you may need to dampen the amount of changes in order to reduce network-wide churn. Use the optional hysteresis keyword with the threshold threshold-value keyword and argument to set a cost change threshold. Any cost change below this threshold is ignored
EIGRP Metric Dampening
Because metric components could be changing rapidly, the frequency of the changes can have an impact on the network. Frequent changes require that prefixes learned though the VMI interface 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
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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, will not be 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, will not be 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, which have outstanding changes to report, will be sent out. If a route changes, such that the final metric of the route matches the last updated metric, no update will be sent.
Neighbor Up/Down Signaling for OSFPv3 and EIGRP
MANETs are highly dynamic environments. Nodes may move into, or out of, radio range at a fast pace. Each time a node joins or leaves, of course, the network topology must be logically reconstructed by the routers. Routing protocols normally use timer-driven "hello" messages or neighbor timeouts to track topology changes, but for 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 routing protocols (OSPFv3 or EIGRP) respond immediately to these signals by expediting 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 will immediately sense the loss and establish 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 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; and reduces impact on radio equipment by minimizing the need for internal queuing/buffering; also provides consistent Quality of Service for networks with multiple radios.
The messaging allows for flexible rerouting when necessary because of
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Figure 3 illustrates the signaling sequence that occurs when radio links go up and down.
Figure 3 Up and Down Signaling Sequence
PPPoE Credit-based Flow Control
Each radio initiates a PPPoE session with its local router as soon as the radio establishes a link to another radio. Once the PPPoE sessions are active for each node, a PPP session is then established end-to-end (router-to-router). This process is duplicated each time a radio establishes a new link.
The carrying capacity of each radio link may vary due to location changes or environmental conditions, and many radio transmission systems have limited buffering capabilities. To minimize the need for packet queuing in the radio, Cisco has implemented extensions to the PPPoE protocol that enable the router to control traffic buffering in congestion situations. Implementing flow-control on these router-to-radio sessions also will allow use of quality of service features such as fair queuing.
The solution utilizes a credit-granting mechanism documented in an IETF informational draft. When the PPPoE session is established, the radio can request a flow-controlled session. If the router acknowledges the request, all subsequent traffic must be flow-controlled. If a flow control session has been requested and cannot be supported by the router, the session is terminated. Typically, both the radio and the router initially grant credits during session discovery. Once a device exhausts its credits, it must stop sending until additional credits have been granted. Credits can be added incrementally over the course of a session.
IPv6 Addresses
You can configure VMI interfaces with IPv6 addresses only, IPv4 addresses only, or both IPv4 and IPv6 addresses.
IPv6 addresses are assigned to individual router interfaces and enable the forwarding of IPv6 traffic globally on the router. By default, IPv6 addresses are not configured and IPv6 routing is disabled.
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The /prefix-length argument in the ipv6 address command is a decimal value that indicates how many of the high-order contiguous bits of the address comprise the prefix (the network portion of the address) A slash mark must precede the decimal value.Restrictions for IPv6 Addressing
In Cisco IOS Release 12.2(4)T or later releases, Cisco IOS Release 12.0(21)ST, and Cisco IOS Release 12.0(22)S or later releases, the ipv6 address or ipv6 address eui-64 command can be used to configure multiple IPv6 global addresses within the same prefix on an interface. Multiple IPv6 link-local addresses on an interface are not supported.
Prior to Cisco IOS Releases 12.2(4)T, 12.0(21)ST, and 12.0(22)S, the Cisco IOS command-line interface (CLI) displays the following error message when multiple IPv6 addresses within the same prefix on an interface are configured as:
Prefix <prefix-number> already assigned to <interface-type>For additional information about IPv6 addressing, see Implementing IPv6 Addressing in the Cisco IOS IPv6 Configuration Guide at the following URL:
http://www.cisco.com/en/US/products/ps6441/products_configuration_guide_chapter09186a00806f3a6a.html
How to Configure Router-to-Radio Links Using VMI PPPoE
This section identifies the tasks that will be used to configure VMI PPPoE. Configuring the VMI PPPoE involves implementing the infrastructure, establishing the IPv4 and IPv6 addressing schemes, and configuring the routing environment. This document contains configuration guidelines only for configuration of PPPoE as it relates to VMIs. For details about configuring PPPoE, refer to the Cisco IOS Broadband and DSL Configuration Guide. For details about PPPoE commands, refer to the Cisco IOS Broadband and DSL Command Reference.
The following sections are included:
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Implementing the VMI Infrastructure Using PPPoE
The PPPoE protocol provides the transport for the mobile network. The following tasks are required to configure PPPoE to support the VMI.
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Creating a Subscriber Profile for PPPoE Service Selection
Perform this task to configure a subscriber profile for PPPoE service selection.
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What to Do Next
After you have defined the PPPoE subscriber profile and service, you must apply the definitions to a BBA group
Configuring the PPPoE Profile for PPPoE Service Selection
Perform this task to associate a subscriber profile with a PPPoE profile. In this configuration, the BBA group name should match the subscriber profile name previously defined in the subscriber profile. In this case, the profile name used as the service name is manet_radio.
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Troubleshooting Tips
Use the show pppoe session and debug pppoe commands to troubleshoot PPPoE sessions.
Configuring PPPoE on an Ethernet Interface
Perform this task to assign a PPPoE profile to an Ethernet interface.
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Implementing the VMI and Configuring the Routing Protocol
The configuration guidelines in this section are all optional, depending on the method and routing protocol that you choose to support the VMI interface.
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Creating and Configuring a Virtual Template for VMI PPPoE
To create and configure a virtual template, use the following commands beginning in global configuration mode. Cisco recommends that, when using the virtual template, you turn off the PPP keepalive messages to make CPU usage more efficient and to help avoid the potential for the router to terminate the connection if PPP keepalive packets are missed over a lossy Radio Frequency (RF) link.
You can configure multiple virtual template interfaces for your VMI PPPoE connections. The selection of which virtual template to use is predicated on the service name sent by the radio during PPPoE session establishment. As an example, consider the following configuration:
subscriber authorization enable!subscriber profile onepppoe service manet_radio_over_x_band!!subscriber profile twopppoe service manet_radio_over_c_band!!!bba-group pppoe onevirtual-template 1service profile one!!bba-group pppoe twovirtual-template 2service profile two!!interface Virtual-Template1...!!interface Virtual-Template2...Using this configuration, any PPPoE request for a session (presentation of a PPPoE Active Discovery Initiate, or PADI packet) with the service name of "manet_radio_over_x_band" would use Virtual-Template1 as the interface to be cloned. Conversely, any PADI presented by the radio with the service name of "manet_radio_over_c_band" would use Virtual-Template2.
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ipv6 enable
or both if both IPv4 and IPv6 are used.DETAILED STEPS
Where To Go Next
Refer to the "Virtual Interface Template Service" chapter in the Cisco IOS Dial Solutions Configuration Guide for additional information about configuring the virtual templates
Creating and Configuring a VMI Interface for EIGRP IPv4
Perform this task to create the VMI interface and associate it with the Ethernet interface on which PPPoE is enabled. When you create a VMI interface, assign the IPv6 or IPv4 address to that VMI interface definition. Do not assign any addresses to the corresponding physical interface.
The radio alerts the router with PADT messages that the layer-2 radio frequency (RF) connection is no longer alive. Cisco recommends that you turn off the PPP keepalive messages to make CPU usage more efficient and to help avoid the potential for the router to terminate the connection if PPP keepalive packets are missed over a lossy RF link.
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Creating and Configuring a VMI interface for EIGRP IPv6
Perform this task to create the VMI interface and associate it with the Ethernet interface on which PPPoE is enabled. When you create a VMI interface, assign the IPv6 address to that VMI interface definition. Do not assign any addresses to the corresponding physical interface.
The radio alerts the router with PADT messages that the layer-2 radio frequency (RF) connection is no longer alive. If you turn off the PPP keepalive messages, it can make CPU usage more efficient and help to avoid the potential for the router to terminate the connection if PPP keepalive packets are missed over a lossy RF link.
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