Chapter 2


List the major entities in a Mobile IP deployment.


Answer: The major entities in a Mobile IP deployment are Mobile Node, Home Agent, and Foreign Agent (or Care-of Address).


Mobile IP provides which of the following features? (Select two.)

  1. A dynamic security association between the Mobile Node and Home Agent that changes as the Mobile Node roams across different subnets

  2. Seamless roaming across IP subnets

  3. Redirection routing to the Mobile Node based on the distance to the Mobile Node's new location

  4. Mobility transparent to Correspondent Nodes

  5. Host-specific routing to the Mobile Node


Answer: b and d. Mobile IP provides seamless roaming across different IP subnets. The Mobile Node maintains communication through its home IP address. Thus, communication is transparent to Correspondent Nodes. A tunnel entry is included in the routing table at the Home Agent to tunnel packets to the Mobile Node.


In Mobile IP, when a Mobile Node moves to another domain, how do the Correspondent Nodes (CNs) now communicate with the Mobile Node?

  1. The Mobile Node informs the Correspondent Node of its movement, and thus a dynamic tunnel is created between the Correspondent Node and the Mobile Node's Care-of Address. The Correspondent Node sends packets for the Mobile Node through the tunnel.

  2. The Correspondent Nodes communicate as normal with the Mobile Node, sending packets to the Mobile Node's home IP address. The Home Agent intercepts the packets and forwards them to the Mobile Node through a dynamic tunnel established between the Home Agent and Care-of-Address.

  3. The Correspondent Nodes sends packets to the home network and requests the Home Agent to tunnel the packets to the Mobile Node through the Mobile Node's Care-of Address.

  4. The Correspondent Node suspends communication with the Mobile Node until the Mobile Node returns home.


Answer: b. Mobility of the Mobile Node is transparent to the CN. The CN communicates with the Mobile Node as normal.


Which two features of a mobility protocol are facilitated by agent advertisements in Mobile IP?

  1. Location discovery

  2. Move detection

  3. Update signaling

  4. Path (re)establishment


Answer: a and b. The agent advertisement can be used for move detection and contains the Care-of Address, which is the location used by Mobile IP.


Which of the following is not used for move detection?

  1. The router address and prefix length extension portion of the agent advertisement

  2. The Care-of Address portion of the agent advertisement

  3. Link-state information

  4. RRQ message


Answer: d. The Mobile Node uses the RRQ message to communicate with its Home Agent after it detects movement.


Mobile IP handover occurs at Layer 2.

  1. True

  2. False


Answer: False. Mobile IP handover occurs at Layer 3 and is independent of Layer 2 handover. Mobile IP handover is the update of the routing table at the Home Agent.


Name three different types of Mobile IP handover policy algorithms. Briefly describe each one.



  • Steady-state algorithm In this algorithm, the Mobile Node holds on to its current Foreign Agent as long as it can. After the Mobile Node establishes a valid registration with a Foreign Agent, it continues to listen for advertisements from other Foreign Agents. However, the Mobile Node cannot register with a new Foreign Agent until the current Foreign Agent's advertisement lifetime has expired.

  • New network algorithm Using the Mobile IP agent advertisement and the prefix length extension, the Mobile Node knows exactly which subnets are available on the current link. When a Mobile Node hears an advertisement on that link, it compares the network prefix(es) of its current Mobility Agent's advertisement against any newly received agent advertisements. If they differ, the Mobile Node can assume that it has roamed and needs to initiate a Mobile IP handover.

  • Link-state triggers Using Layer 2 information along with Mobile IP agent solicitations, the Mobile Node can determine even more quickly whether it has moved.


How does a Mobile Node know whether it is on its Home Network or a Foreign Network?

  1. By comparing the lifetime granted in its current Mobile IP registration against that advertised in Mobile IP agent advertisements

  2. By comparing the FA address configured on the Mobile Node against that advertised in the Mobile IP agent advertisements

  3. By comparing its CoA against the Home Agent address advertised in Mobile IP agent advertisements

  4. By comparing its Home Address and network prefix against those advertised in Mobile IP agent advertisements


Answer: d. Upon hearing a Mobile IP agent advertisement, the Mobile Node can compare its network prefix against that advertised. It can thus discern whether it is at home or roaming.


A Mobile Node finds itself away from home on a network with a FA. Describe the Mobile IP registration process, starting with how the Mobile Node learns that it is not home.


Answer: The Mobile Node hears an agent advertisement from a Foreign Agent and determines that it is roaming by comparing its Home Network prefix against that in the advertisement. The Mobile Node learns the Care-of Address from the advertisement. It sends a RRQ to the Home Agent through the Foreign Agent. The Home Agent authenticates the RRQ and processes the request. It sends a RRP to the Mobile Node through the Foreign Agent. In the RRP, the Home Agent grants the registration lifetime for the Mobile Node.


What types of CoAes can a Mobile Node use on a Foreign Network?


Answer: A Mobile Node can use a Foreign Agentbased Care-of Address and a Colocated Care-of Address on a Foreign Network.


Which of the following are advantages of a Mobile Node using a FA CoA? (Select two.)

  1. Many Mobile Nodes can roam off of the same CoA, which saves address space in IPv4.

  2. The Mobile Node can retain the same FA CoA as it moves across different foreign domains.

  3. The Mobile Node can be preconfigured with the FA CoA.

  4. The same tunnel between the Home Agent and FA can support numerous Mobile Nodes.

  5. The Mobile Node does not need to reregister with its Home Agent when it moves to a different foreign domain.


Answer: a and d. As the Mobile Node roams across different foreign domains, it can obtain a different Care-of Address.


Which of the following indicate situations when the Mobile Node would use a Colocated CoA? (Select two.)

  1. If the Mobile Node is statically configured with a Colocated CoA

  2. If the Mobile Node doesn't hear an agent advertisement from a FA on the foreign domain

  3. If the Mobile Node doesn't hear an agent advertisement from its Home Agent on the foreign domain

  4. If the Mobile Node cannot detunnel its own packets

  5. If the FA is not providing services that the Mobile Node would like


Answer: b and e.


How does a Mobile Node signify to the Home Agent that it would like a dynamic Home Address to be assigned?


Answer: The Mobile Node sets the Home Address field in the RRQ to


Describe the steps that a FA follows during the registration process.


Answer: When a Foreign Agent receives an RRQ, it first verifies any necessary security associations. If the Foreign Agent cannot or will not provide the requested services, it generates an RRP with an appropriate failure code. If the Foreign Agent is willing and able to provide all the requested services, it creates an entry in the pending registration table. A pending registration is held by the Foreign Agent for a maximum of 7 seconds before assuming that the Home Agent is unavailable. If an RRP is not received from the Home Agent, the Foreign Agent generates an RRP with a "registration timeout" error code. If the Foreign Agent receives the RRP from the Home Agent and deems the reply valid, it moves the pending registration entry into the visitor table.


Describe the steps that the Home Agent follows upon receiving a RRQ from a Mobile Node.


Answer: When the Home Agent receives the RRQ, it begins by verifying all security associations. After the authenticity of the RRQ has been verified, the Home Agent either updates the Mobile Node's binding, if it already exists in the binding table, or creates a new binding for the Mobile Node in the binding table. If a Mobile Node is requesting that a Home Address be dynamically assigned, the Home Agent receives an RRQ with a Home Address of Before the binding is created, the Home Agent allocates an address to the Mobile Node that the Mobile Node retains for as long as its binding is active. The Home Agent includes the dynamically assigned address in the Home Address field of the RRP. When the registration has been accepted, the Mobile IP tunnel created, and the routing table updated, the Home Agent sends a gratuitous ARP on the Home Network to ensure that all traffic for the Mobile Node is delivered to the Home Agent. Finally, the Home Agent builds the HA-MN authenticator and sends an RRP to the CoA.


What is triangle routing?


Answer: Traffic for the Mobile Node goes from the Correspondent Node to the Home Agent to the Mobile Node, and return traffic goes directly from the Mobile Node to the Correspondent Node, bypassing the Home Agent, thus forming a triangular path.


What does a Mobile Node do upon returning home?


Answer: Upon returning home, a Mobile Node sends a deregistration message to the Home Agent, allowing the Home Agent to delete the mobility binding.

    Mobile IP Technology and Applications
    Mobile IP Technology and Applications
    ISBN: 158705132X
    EAN: 2147483647
    Year: 2005
    Pages: 124

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