MANET Enhancements to PPPoE for Router-to-Radio Links

Mobile Ad Hoc Networks (MANETs) for device-to-radio communications address the challenges faced when merging IP routing and mobile radio communications in ad hoc networking applications:

• Optimal route selection based on Layer 2 feedback from the radio network
• Faster convergence when nodes join and leave the network because devices are able to respond faster to network topology changes
• Efficient integration of point-to-point, directional radio topologies with multihop routing
• Flow-controlled communications between each radio and its partner device enables applications such as voice and video to work better because outages caused by moving links are reduced or eliminated. Sessions are more stable and remain active longer

Through the device-to-radio link, the radio can inform the device immediately when a node joins or leaves, and this enables the device to recognize topology changes more quickly than if it had to rely on timers. Without this link-status notification from the radio, the device would likely time out while waiting for traffic. The link-status notification from the radio enables the device to respond faster to network topology changes. Metric information regarding the quality of a link is passed between the device and radio, enabling the device to more intelligently decide on which link to use.

With the link-status signaling provided by the device-to-radio link, applications such as voice and video work better because outages caused by topology changes are reduced or eliminated. Sessions are more stable and remain active longer.

Cross-layer feedback for device-to-radio integration of Radio-Aware Routing (RAR) takes advantage of the functions defined in RFC 5578. The RFC 5578 is an Internet Engineering Task Force (IETF) standard that defines PPP over Ethernet (PPPoE) extensions for Ethernet-based communications between a device and a mobile radio, that operates in a variable-bandwidth environment and has limited buffering capabilities. These extensions provide a PPPoE session-based mechanism for sharing radio network status such as link-quality metrics and establishing flow control between a device and an RAR-compliant radio.

An RAR-compliant radio initiates a Layer 2 PPPoE session with its adjacent device on behalf of every device and radio neighbor discovered in the network. These Layer 2 sessions are the means by which radio network status for each neighbor link is reported to the device. The radio establishes the correspondence between each PPPoE session and each link to a neighbor.

Mobile Ad Hoc Networks (MANETs) enable users deployed in areas with no fixed communications infrastructure to access critical voice, video, and data services. For example, 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 multiagency 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.

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 device, with the two devices interconnected over an Ethernet. Because 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 device network.

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 multihop, multipoint device environments because it increases the size of each device's topology database and reduces routing efficiency.

Effective networking in a MANET environment therefore requires mechanisms by which

• Devices and radios can interoperate efficiently, and without impacting operation of the radio network.
• Radio point-to-point and device point-to-multipoint paradigms can be rationalized.
• Radios can report status to devices for each link and each neighbor.
• Devices can use this information to optimize routing decisions.

The Mobile Ad Hoc Network (MANET) implementation uses PPP over Ethernet (PPPoE) sessions to enable intranodal communications between a device 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 (device-to-device). This is duplicated each time a radio establishes a new radio link. The virtual multipoint interface (VMI) on the device can aggregate multiple PPPoE sessions and multiplex them to look like a single interface to the routing processes. Underneath the VMI are virtual access interfaces that are associated with each of the PPP and PPPoE connections.

A PPPoE session is established between a device and a radio on behalf of every other device and 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 device. The figure below shows the PPPoE session exchange between mobile devices and directional radios in a MANET network.

This capability requires that a Radio-Aware Routing (RAR)-compliant radio be connected to a device through Ethernet. The device always considers the Ethernet link to be up. If the radio side of the link goes down, the device waits until a routing update timeout occurs to declare the route down and then updates the routing table. The figure below shows a simple device-to-radio link topology.

The routing protocols optimized for VMI PPPoE are Enhanced Interior Gateway Routing Protocol (EIGRP) (IPv4, IPv6) and Open Shortest Path First version 3 (OSPFv3) for IPv4 and IPv6.

The virtual multipoint interface (VMI) provides services that map outgoing packets to the appropriate PPP over Ethernet (PPPoE) sessions based on the next-hop forwarding address for that packet. The VMI 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 in aggregate mode, VMI replicates the packet and sends it through the virtual access interfaces 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. However, the routing processes in Mobile Ad Hoc Networks (MANETs) operate most efficiently because the network link is treated as point-to-multipoint, with broadcast capability. For the device, modeling the MANET as a collection of point-to-point nodes has a dramatic impact on the size of its internal database.

The VMI within the device can aggregate 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, multiaccess, 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. The VMI signals are used by the Enhanced Interior Gateway Routing Protocol (EIGRP) for IPv4 and IPv6 neighbors and the Open Shortest Path First version 3 (OSPFv3) for IPv6 neighbors.

You can configure virtual multipoint interfaces (VMIs) with IPv6 addresses only, IPv4 addresses only, or both IPv4 and IPv6 addresses.

IPv6 addresses are assigned to individual device interfaces and enable the forwarding of IPv6 traffic globally on the device. By default, IPv6 addresses are not configured and IPv6 routing is disabled.

Note

The ipv6-address argument in the ipv6 address command must be in the form documented in RFC 2373 where the address is specified in hexadecimal using 16-bit values between colons. 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

The Open Shortest Path First version 3 9OSPFv3) address family feature is implemented according to RFC 5838 and enables the concurrent routing of IPv4 and IPv6 prefixes.

When this feature is enabled with Mobile Ad Hoc Networks (MANETs), IPv6 packets are routed in mobile environments over OSPFv3 using IPv4 or IPv6 addresses.

For configuration details, see the IP Routing: OSPF Configuration Guide.

Mobile Ad Hoc Networks (MANETs) are highly dynamic environments. Nodes might move into, 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 devices. Routing protocols normally use timer-driven hello messages or neighbor timeouts to track topology changes, but MANETs reliance on these mechanisms can result in unacceptably slow convergence.

The neighbor up/down signaling capability provides faster network convergence by using link-status signals generated by the radio. The radio notifies the device each time a link to another neighbor is established or terminated by the creation and termination of PPP over Ethernet (PPPoE) sessions. In the device, the routing protocols (Open Shortest Path First version 3 [OSPFv3] or Enhanced Interior Gateway Routing Protocol [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 device 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 virtual multipoint interfaces (VMIs) with PPPoE are used and a partner node has left or a new one has joined, the radio informs the device immediately of the topology change. Upon receiving the signal, the device immediately declares the change and updates the routing tables. The signaling capability provides these advantages:

• 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 queueing and buffering
• Provides consistent quality of service for networks with multiple radios

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

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

The figure below shows the signaling sequence that occurs when radio links go up and down.

Each radio initiates a PPP over Ethernet (PPPoE) session with its local device 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 (device-to-device). This process is duplicated each time a radio establishes a new link.

The carrying capacity of each radio link might vary due to location changes or environmental conditions, and many radio transmission systems have limited buffering capabilities. To minimize the need for packet queueing in the radio, PPPoE protocol extensions enable the device to control traffic buffering in congestion situations. Implementing flow-control on these device-to-radio sessions allows use of quality of service (QoS) features such as fair queueing.

The flow-control solution utilizes a credit-granting mechanism documented in RFC 5578. When the PPPoE session is established, the radio can request a flow-controlled session. If the device acknowledges the request, all subsequent traffic must be flow controlled. If a flow-control session is requested and cannot be supported by the device, the session is terminated. Typically, both the radio and the device initially grant credits during session discovery. Once a device exhausts its credits, it must stop sending until additional credits are granted. Credits can be added incrementally over the course of a session.

Metrics scaling is used with high-performance radios that require high-speed links. The radio can express the maximum and current data rates with different scaler values. Credit scaling allows a radio to change the default credit grant (or scaling factor) of 64 bytes to its default value. You can display the maximum and current data rates and the scalar value set by the radio in the show vmi neighbor detail command output.

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    subscriber profile profile-name

4.    pppoe service manet_radio

5.    exit

6.    subscriber authorization enable

7.    exit

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Device> enable	Enables privileged EXEC mode. Enter your password if prompted.
Step 2	configure terminal Example: Device# configure terminal	Enters global configuration mode.
Step 3	subscriber profile profile-name Example: Device(config)# subscriber profile manet	Enters subscriber profile configuration mode.
Step 4	pppoe service manet_radio Example: Device(config-sss-profile)# pppoe service manet_radio	Adds a PPPoE MANET radio service name to a subscriber profile to enable the use of the VMI.
Step 5	exit Example: Device(config-sss-profile)# exit	Returns to global configuration mode.
Step 6	subscriber authorization enable Example: Device(config)# subscriber authorization enable	Enable Subscriber Service Switch type authorization. This command is required when virtual private dialup networks (VPDNs) are not used.
Step 7	exit Example: Device(config)# exit	Returns to privileged EXEC mode.

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    bba-group pppoe {group-name | global}

4.    virtual-template template-number

5.    service profile subscriber-profile-name [refresh minutes]

6.    end

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Device> enable	Enables privileged EXEC mode. Enter your password if prompted.
Step 2	configure terminal Example: Device# configure terminal	Enters global configuration mode.
Step 3	bba-group pppoe {group-name | global} Example: Device(config)# bba-group pppoe group1	Defines a PPPoE profile and enters BBA group configuration mode. The global keyword creates a profile that serves as the default profile for any PPPoE port that is not assigned a specific profile.
Step 4	virtual-template template-number Example: Device(config-bba-group)# virtual-template 1	Specifies which virtual template will be used to clone virtual access interfaces for all PPPoE ports that use this PPPoE profile.
Step 5	service profile subscriber-profile-name [refresh minutes] Example: Device(config-bba-group)# service profile subscriber-group1	Assigns a subscriber profile to a PPPoE profile. The PPPoE server advertises the service names that are listed in the subscriber profile to each PPPoE client connection that uses the configured PPPoE profile. Use the refresh minutes keyword and argument to cause the cached PPPoE configuration to time out after a specified number of minutes.
Step 6	end Example: Device(config-bba-group)# end	(Optional) Returns to privileged EXEC mode.

• Troubleshooting Tips

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    interface type number

4.    pppoe enable [group group-name]

5.    end

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Device> enable	Enables privileged EXEC mode. Enter your password if prompted.
Step 2	configure terminal Example: Device# configure terminal	Enters global configuration mode.
Step 3	interface type number Example: Device(config)# interface fastethernet 3/1	Specifies an interface and enters interface configuration mode. Ethernet, Fast Ethernet, Gigabit Ethernet, VLANs, and VLAN subinterfaces can be used.
Step 4	pppoe enable [group group-name] Example: Device(config-if)# pppoe enable group bba1	Enables PPPoE sessions on an interface or subinterface.
Step 5	end Example: Device(config-if)# end	(Optional) Returns to privileged EXEC mode.

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    interface virtual-template number

4.    Perform steps 5 and 8 if you are using IPv4. Perform steps 6, 7, and 8 if you are using IPv6. If you are using both, perform steps 5, 6, 7, and 8.

5.    ip unnumbered interface-type interface-number

6.    ipv6 enable

7.    ipv6 unnumbered interface-type interface-number

8.    end

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Device> enable	Enables privileged EXEC mode. Enter your password if prompted.
Step 2	configure terminal Example: Device# configure terminal	Enters global configuration mode.
Step 3	interface virtual-template number Example: Device(config)# interface virtual-template 1	Creates a virtual template, and enters interface configuration mode.
Step 4	Perform steps 5 and 8 if you are using IPv4. Perform steps 6, 7, and 8 if you are using IPv6. If you are using both, perform steps 5, 6, 7, and 8. Example: Example:	--
Step 5	ip unnumbered interface-type interface-number Example: Device(config-if)# ip unnumbered vmi 1	Enables IP processing of IPv4 on an interface without assigning an explicit IP address to the interface.
Step 6	ipv6 enable Example: Device(config-if)# ipv6 enable	Enables IPv6 processing on the interface.
Step 7	ipv6 unnumbered interface-type interface-number Example: Device(config-if)# ipv6 unnumbered vmi I	Enables IPv6 processing on an interface without assigning an explicit IPv6 address to the interface.
Step 8	end Example: Device(config-if)# end	(Optional) Returns to privileged EXEC mode.

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    ip routing

4.    no virtual-template subinterface

5.    policy-map policy-mapname

6.    class class-default

7.    fair-queue

8.    exit

9.    exit

10.    interface virtual-template number

11.    ip unnumbered interface-type interface-number

12.    service-policy output policy-mapname

13.    no keepalive

14.    interface type number

15.    ip address address mask

16.    no ip redirects

17.    no ip split-horizon eigrp autonomous-system-number

18.    physical-interface type number

19.    exit

20.    router eigrp autonomous-system-number

21.    network network-number ip-mask

22.    redistribute connected

23.    end

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Device> enable	Enables privileged EXEC mode. Enter your password if prompted.
Step 2	configure terminal Example: Device# configure terminal	Enters global configuration mode.
Step 3	ip routing Example: Device(config)# ip routing	Enables IP routing on the device.
Step 4	no virtual-template subinterface Example: Device(config)# no virtual-template subinterface	Disables the virtual template on the subinterface.
Step 5	policy-map policy-mapname Example: Device(config)# policy-map fair-queue	Enters QoS policy-map configuration mode and creates or modifies a policy map that can be attached to one or more interfaces to specify a service policy.
Step 6	class class-default Example: Device(config-pmap)# class class-default	Specifies the name of the class whose policy you want to create or change or specifies the default class (commonly known as the class-default class) before you configure its policy. Enters Qos policy-map class configuration mode.
Step 7	fair-queue Example: Device(config-pmap-c)# fair-queue	Enables weighted fair queueing (WFQ) on the interface.
Step 8	exit Example: Device(config-pmap-c)# exit	Returns to QoS policy-map configuration mode.
Step 9	exit Example: Device(config-pmap)# exit	Returns to global configuration mode.
Step 10	interface virtual-template number Example: Device(config)# interface virtual-template 1	Enters interface configuration mode and creates a virtual template interface that can be configured and applied dynamically in creating virtual access interfaces.
Step 11	ip unnumbered interface-type interface-number Example: Device(config-if)# ip unnumbered vmi 1	Enables IP processing of IPv4 on a serial interface without assigning an explicit IP address to the interface.
Step 12	service-policy output policy-mapname Example: Device(config-if)# service-policy output fair-queue	Attaches a policy map to an input interface, virtual circuit (VC), or to an output interface or VC. The policy map is as the service policy for that interface or VC.
Step 13	no keepalive Example:no Device(config-if)# no keepalive	Turns off PPP keepalive messages to the interface.
Step 14	interface type number Example: Device(config-if)# interface vmi 1	Specifies the number of the VMI.
Step 15	ip address address mask Example: Device(config-if)# ip address 209.165.200.225 255.255.255.224	Specifies the IP address of the VMI.
Step 16	no ip redirects Example: Device(config-if)# no ip redirects	Disables the sending of Internet Control Message Protocol (ICMP) redirect messages if the Cisco software is forced to resend a packet through the same interface on which it was received.
Step 17	no ip split-horizon eigrp autonomous-system-number Example: Device(config-if)# no ip split-horizon eigrp 101	Disables the split horizon mechanism for the specified session.
Step 18	physical-interface type number Example: Device(config-if)# physical-interface FastEthernet 0/1	Creates the physical subinterface to be associated with the VMIs on the device.
Step 19	exit Example: Device(config-if)# exit	Exits interface configuration mode and returns to global configuration mode.
Step 20	router eigrp autonomous-system-number Example: Device(config)# router eigrp 100	Enables EIGRP routing on the device, identifies the autonomous system number, and enters router configuration mode.
Step 21	network network-number ip-mask Example: Device(config-router)# network 209.165.200.225 255.255.255.224	Identifies the EIGRP network.
Step 22	redistribute connected Example: Device(config-router)# redistribute connected	Redistributes routes from one routing domain into another routing domain.
Step 23	end Example: Device(config-router)# end	(Optional) Returns to privileged EXEC mode.

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    no virtual-template subinterface

4.    ipv6 unicast-routing

5.    ipv6 cef

6.    policy-map policy-mapname

7.    class class-default

8.    fair-queue

9.    exit

10.    exit

11.    interface virtual-template number

12.    ipv6 enable

13.    no keepalive

14.    service-policy output policy-mapname

15.    interface type number

16.    ipv6 address address/prefix-length

17.    ipv6 enable

18.    ipv6 eigrp as-number

19.    no ipv6 redirects

20.    no ipv6 split-horizon eigrp as-number

21.    physical-interface type number

22.    no shutdown

23.    ipv6 router eigrp as-number

24.    redistribute connected

25.    end

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Device> enable	Enables privileged EXEC mode. Enter your password if prompted.
Step 2	configure terminal Example: Device# configure terminal	Enters global configuration mode.
Step 3	no virtual-template subinterface Example: Device(config)# no virtual-template subinterface	Disables the virtual template on the subinterface.
Step 4	ipv6 unicast-routing Example: Device(config)# ipv6 unicast-routing	Enables IPv6 unicast routing.
Step 5	ipv6 cef Example: Device(config)# ipv6 cef	Enables IPv6 Cisco Express Forwarding on the device
Step 6	policy-map policy-mapname Example: Device(config-pmap)# policy-map fair-queue	Enters QoS policy-map configuration mode and creates or modifies a policy map that can be attached to one or more interfaces to specify a service policy.
Step 7	class class-default Example: Device(config-pmap)# class class-default	Specifies the name of the class whose policy you want to create or change or specifies the default class (commonly known as the class-default class) before you configure its policy. Enters QoS policy-map class configuration mode.
Step 8	fair-queue Example: Device(config-pmap-c)# fair-queue	Enables weighted fair queueing (WFQ) on the interface.
Step 9	exit Example: Device(config-pmap-c)# exit	Returns to QoS policy-map configuration mode.
Step 10	exit Example: Device(config-pmap)# exit	Returns to global configuration mode.
Step 11	interface virtual-template number Example: Device(config)# interface virtual-template 1	Enters interface configuration mode and creates a virtual template interface that can be configured and applied dynamically in creating virtual access interfaces.
Step 12	ipv6 enable Example: Device(config-if)# ipv6 enable	Enables IPv6 routing on the virtual template.
Step 13	no keepalive Example: Device(config-if)# no keepalive	Turns off PPP keepalive messages to the virtual template.
Step 14	service-policy output policy-mapname Example: Device(config-if)# service-policy output fair-queue	Attaches a policy map to an input interface, virtual circuit (VC), or to an output interface or VC. The policy map is as the service policy for that interface or VC.
Step 15	interface type number Example: Device(config-if)# interface vmi 1	Creates a VMI.
Step 16	ipv6 address address/prefix-length Example: Device(config-if)# ipv6 address 2001:0DB8::/32	Specifies the IPv6 address for the interface.
Step 17	ipv6 enable Example: Device(config-if)# ipv6 enable	Enables IPv6 routing on the interface.
Step 18	ipv6 eigrp as-number Example: Device(config-if)# ipv6 eigrp 1	Enables the EIGRP for IPv6 on a specified interface and specifies the autonomous system number.
Step 19	no ipv6 redirects Example: Device(config-if)# no ipv6 redirects	Disables the sending of Internet Control Message Protocol (ICMP) IPv6 redirect messages if the software is forced to resend a packet through the same interface on which the packet was received
Step 20	no ipv6 split-horizon eigrp as-number Example: Device(config-if)# no ipv6 split-horizon eigrp 100	Disables the split horizon for EIGRP IPv6. Associates this command with a specific EIGRP autonomous system number.
Step 21	physical-interface type number Example: Device(config-if)# physical-interface FastEthernet 1/0	Creates the physical subinterface to be associated with the VMIs on the device.
Step 22	no shutdown Example: Device(config-if)# no shutdown	Restarts a disabled interface or prevents the interface from being shut down.
Step 23	ipv6 router eigrp as-number Example: Device(config-if)# ipv6 router eigrp 100	Places the device in router configuration mode, creates an EIGRP routing process in IPv6, and allows you to enter additional commands to configure this process.
Step 24	redistribute connected Example: Device(config-router)# redistribute connected	Allows the target protocol to redistribute routes learned by the source protocol and connected prefixes on those interfaces over which the source protocol is running. Redistributes IPv6 routes from one routing domain into another routing domain.
Step 25	end Example: Device(config-router)# end	(Optional) Returns to privileged EXEC mode.

You can use the following commands to verify the virtual multipoint interface (VMI) configuration:

• show pppoe session all
• show interface vmi
• show vmi neighbors
• show vmi neighbors detail
• show ip eigrp interfaces
• show ip eigrp neighbors
• show ipv6 eigrp interfaces
• show ipv6 eigrp neighbors
• show ipv6 ospf interface