Chapter 7


1:

Cisco Mobile Networks is a mobility solution that provides which of the following? (Select three.)

  1. Dynamic host routing propagation to clients on the mobile router.

  2. The devices connected to the mobile router do not need to be Mobile IP aware because the MR is providing the roaming capabilities.

  3. FA redundancy for transparent FA failure between the mobile router and FA.

  4. Packets destined to the mobile router are double encapsulated. The Home Agent forwards packets destined to the mobile networks to the FA, which then forwards the packets to the mobile router, which then forwards to the devices on its networks.

  5. It allows entire network(s) to roam.

A1:

Answer: b, d, and e: Cisco Mobile Networks allows entire networks to roam. It is ideal for airplanes, ships, and trains, that is, any architecture where the entire network is in motion.

2:

In network mobility, how does the Home Agent know which mobile networks are connected to a mobile router?

A2:

Answer: This can either be done through static configuration of the mobile networks or through dynamic updates during the Mobile IP registration process.

3:

What is the roaming interface?

A3:

Answer: Roaming interfaces are used as the gateway between the mobile networks and the rest of the network.

4:

What is the preferred path feature, and why is it needed?

A4:

Answer: The mobile router can obtain Layer 2 connections on different interfaces and therefore must decide on which interface to roam and register. Preferred path allows the mobile router to select the best interface on which to roam and register based on a priority.

5:

What is the hold down period? Describe its purpose.

A5:

Answer: After hearing a Foreign Agent's advertisement, the mobile router waits the hold down period before deciding to use the agent. The hold down period allows the mobile router to be sure that a link is reliable enough to hear the agent for a period of time before committing to use the agent. The mobile router avoids prematurely registering with a Foreign Agent on a lossy wireless link.

6:

Draw a diagram showing routing to and from a mobile router.

A6:

Answer:

7:

What additional processing over standard Mobile IP must the Home Agent do to support network mobility?

A7:

Answer: The Home Agent must inject the mobile networks into its forwarding table so that routing protocols configured on it can redistribute these mobile routes. The mobile router must also create an additional tunnel to the mobile router's Home Address and add routes to the mobile networks through this tunnel. The Home Agent then advertises reachability to these mobile networks through the Interior Gateway Routing Protocol (IGRP), thereby attracting packets that are destined to nodes on the mobile networks.

8:

Draw a diagram depicting the dual tunnels used in network mobility.

A8:

Answer:

9:

For IOS Mobile Networks, why is another tunnel needed inside the standard Home Agent CoA tunnel?

A9:

Answer: This second tunnel is required because if a Foreign Agent is in use, it only has a route to the Home Address. Packets destined to the mobile networks would follow the standard routing back to the Home Agent and end up in a routing loop.

10:

What is the Priority Home Agent Assignment feature?

A10:

Answer: The Cisco Mobile NetworksPriority Home Agent Assignment feature allows a mobile router to select a closer Home Agent when it is roaming. The mobile router can select a preferred Home Agent from a set of configured Home Agents based on a combination of existing Home Agent priority configurations on the mobile router and Care-of Address access lists configured on the Home Agent.

11:

What caveats are involved with using the Priority Home Agent Assignment feature?

A11:

Answer: If the Mobile Node changes the preferred Home Agent, the IGP must converge before the forwarding path is optimized. While the IGP is reconverging, packets can bounce around the network following stale routes. In some cases, these packets can be lost.

Answer: The same Home Network needs to be configured on all Home Agents. You cannot make the Home Address reachable through the Home Agent that is in use without injecting host routes into the network. Host routing would defeat the purpose of Mobile IP. You should use a route map to prevent the Home Network from even being redistributed into the IGP and use an address from the mobile network for management of the mobile router.

12:

By using the Cisco FA Optimized Routing for Mobile Networks, the FA can do which of the following?

  1. It can directly set up a visitor entry between a node on a visiting mobile router and a CN, and tunnel traffic to the CN.

  2. It can directly receive traffic from a CN and tunnel the traffic to a visiting mobile router.

  3. It can directly send traffic from a CN that is directly connected to it, to a node on a mobile network of one of its visiting mobile routers.

  4. It can directly send traffic from a node on one of its visiting mobile routers to a node on another visiting mobile router.

A12:

Answer: c. Traffic from a Correspondent Node that is directly connected to a Foreign Agent can be sent to a node on a visiting mobile network without having to traverse the Home Agent.

13:

Briefly describe the Mobile Router Redundancy feature.

A13:

Answer: The Mobile Router Redundancy feature leverages HSRP and provides a backup mechanism in case the mobile router fails. One mobile router in the redundancy group is deemed the active mobile router, with the other mobile routers in passive mode. The active mobile router is the router responsible for registering with the Home Agent and for maintaining an active mobility binding. If the active mobile router fails, one of the passive mobile routers is selected as the new active mobile router based on a priority selection algorithm. Upon becoming the new active mobile router, a mobile router sends an agent solicitation out of its roaming interfaces to learn about the existing Foreign Agents and registers back with its Home Agent.

14:

Mobile IP traffic is sent on one link and received on another link in which of the following?

  1. Nested Mobile IP tunnels

  2. Asymmetric links

  3. Bidirectional links

  4. Simultaneous bindings

A14:

Answer: b. If a mobile router and Foreign Agent communicate through asymmetric links, the Foreign Agent receives the mobile router's RRQ on an interface different from the one on which it sent its agent advertisement. Also, the Foreign Agent forwards the RRP to the mobile router on an interface different from the one on which it received the RRQ.

15:

How are QoS features added to the dynamic tunnels established in network mobility, that is, the tunnel between the Home Agent and FA, and the tunnel between the Home Agent and mobile router?

A15:

Answer: Tunnel interface templates are used. Using a tunnel template, QoS preclassification (the qos-preclassify command) can be applied to the tunnel, allowing the original packet header to classify the packet on the outbound interface instead of the Mobile IP tunnel header. It lets the router peek into the original packet and use the QoS credentials of that packet, allowing certain traffic types to receive preferential treatment over the Mobile IP tunnel.



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

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