Answers to Review Questions Dbw

2. Both private and public IPv4 addresses might be required in a network that requires Internet connectivity but that does not require all its end systems to be publicly accessible.

3. Answer:

■ The address is a Class B address.

■ The host part is binary 0101 (decimal 5).

■ The network part is 172.17.7.binary 1111xxxx (decimal 172.17.7.240).

■ 24 - 2 = 14 hosts can reside on this subnet.

4. Information that must be collected to determine the size of the network includes the number and type of locations, the number of devices in each location (such as workstations, router interfaces, and so on) that need addresses and their addressing requirements, and the size of the subnet required.

5. The commonly suggested reserve in the number of network device addresses is 20 percent for main and regional offices and 10 percent for remote offices. Depending on the circumstances, more reserve might be required.

6. Classless routing protocols support VLSM.

7. The router could advertise the 10.5.16.0/22 summary route to represent these four subnets.

8. Some disadvantages of a poorly designed IP addressing scheme include the following:

■ Excess routing traffic, which consumes bandwidth

■ Increased routing table recalculation

■ The possibility of routing loops

9. A hierarchical IP addressing scheme supports route summarization, which reduces routing overhead and the bandwidth required for routing traffic.

10. With classful routing, routing updates do not carry the subnet mask; with classless routing, routing updates carry the subnet mask.

11. DHCP relieves the administrator of the task of manually assigning an address to every device and makes it easier to reconfigure addresses.

12. DHCP supports three possible address allocation mechanisms:

■ Manual: The network administrator assigns the IP address to a specific MAC address. DHCP is used to dispatch the assigned address to the host.

■ Automatic: DHCP assigns a permanent IPv4 address to a host.

■ Dynamic: DHCP assigns an IP address to a host for a limited time (called a lease) or until the host explicitly releases the address. This mechanism allows automatic address reuse when the host to which it has been assigned no longer needs the address.

13. Dynamic name resolution reduces administrative overhead.

14. Answer:

Step 1 A user wants to browse www.cisco.com. The host queries the DNS server because it does not know that site's IP address.

Step 2 The DNS server responds with the appropriate IP address for www.cisco.com.

Step 3 The host establishes the connection to the appropriate IP address (the www.cisco.com site).

15. An IPv6 address has 128 bits.

16. The IPv6 packet header is 40 octets, or 320 bits.

18. A packet that is sent to an anycast address goes to the closest interface (as determined by the routing protocol being used) identified by the anycast address.

19. One-to-many IPv6 addresses are called multicast.

20. True

21. 64 bits are used for the interface ID in an IPv6 unicast address.

22. FE80::/10, the prefix for link-local addresses, is used by devices on the same network to communicate.

23. IPv6 address assignment can be done with static addresses, link-local addresses, stateless autoconfiguration, and DHCPv6.

24. A router on the link advertises—either periodically or at the host's request—network information, such as the 64-bit prefix of the local network and its willingness to function as a default router for the link. Hosts can automatically generate their global IPv6 addresses by using the prefix in these router messages; the hosts do not need manual configuration or the help of a device such as a DHCP server.

25. The A6 record, which is an address record for an IPv6 host, allows DNS to support IPv6.

26. Yes; this is called a dual-stack host.

27. Dual stack, tunneling, and translation are three mechanisms for transitioning from IPv4 to IPv6.

28. The 6-to-4 tunneling method automatically connects IPv6 islands through an IPv4 network. Each 6-to-4 edge router has an IPv6 address with a /48 prefix, which is the concatenation of 2002::/16 and the IPv4 address of the edge router; 2002::/16 is a specially assigned address range for the purpose of 6-to-4. The edge routers automatically build the tunnel using the IPv4 addresses that are embedded in the IPv6 addresses.

When the edge router receives an IPv6 packet with a destination address in the range of 2002::/16, it determines from its routing table that the packet must traverse the tunnel. The router extracts the IPv4 address embedded in the third to sixth octets, inclusive, in the IPv6 next-hop address. This IPv4 address is the IPv4 address of the 6-to-4 router at the destination site—the router at the other end of the tunnel. The router encapsulates the IPv6 packet in an IPv4 packet with the destination edge router's extracted IPv4 address.

The packet passes through the IPv4 network. The destination edge router unencapsulates the IPv6 packet from the received IPv4 packet and forwards the IPv6 packet to its final destination. A 6-to-4 relay router, which offers traffic forwarding to the IPv6 Internet, is required for reaching a native IPv6 Internet.

29. Cisco routers support the following:

30. RIPng uses the multicast address FF02::9, the all-RIP-routers multicast address, as the destination address for RIP updates.

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