Chapter 1
| 1: | What is the size in bits of the IPv4 address scheme? |
| A1: | Answer: IPv4 is based on a 32-bit address scheme. |
| 2: | Which classes of IPv4 addresses are not considered globally unique unicast IP addresses? |
| A2: | Answer: Class D (multicast) and Class E (experimental) are not used as globally unique unicast IP addresses by hosts and routers on the Internet. Although the private addresses are within the range of unicast addresses, they must not be considered globally unique, because many organizations use them inside their network only. |
| 3: | What is the main rationale behind IPv6? |
| A3: | Answer:
The IPv4 address scheme is limited by being 32-bit. Some parts of the address scheme cannot be used as globally unique unicast addresses (Class D, Class E, loopback, 0.0.0.0, private addresses). Very large blocks of addresses are assigned to organizations. The size of the global Internet routing table is huge. NAT is deployed everywhere. It saves globally unique unicast addresses but breaks IP's end-to-end model. The Internet is still growing. Address exhaustion is projected to occur during the current decade. There is enough time to design an update of the current protocol. |
| 4: | Explain the consequences of the exhaustion of the IPv4 address space. |
| A4: | Answer:
New IPv4 address space will be impossible to get. There are not enough globally unique unicast addresses for every device, but the number of new devices requiring IP addresses (such as PDAs and cell phones) is increasing. |
| 5: | Describe the short history of IPv6 from 1993 to 2000. |
| A5: | Answer:
1993: IETF IPng working group. 1995: First specifications for IPv6. 1996: 6bone is started using prefix 3ffe::/16. 1997: Provider-based address format. 1998: First IPv6 exchange is deployed. 1999: ARIN, RIPE, and APNIC are assigned IPv6 spaces to Tier-1 providers using 2001::/16. 1999: IPv6 Forum is founded. 2000: Cisco announces support for IPv6 in its IOS. |
| 6: | Name some limitations of NAT. |
| A6: | Answer:
It breaks the end-to-end model of IP. The network must handle connections and state. It causes problems for networks with fast rerouting, links, and route redundancy. It hinders network performance. Keeping records of all connections becomes mandatory for providers and organizations that must have records for security reasons. NAT modifies the IP header. This affects end-to-end security protocols such as IPSec AH. Applications that are not NAT-friendly cannot pass through NAT. Address space collisions are frequent when organizations merge networks. Private addressing is recommended behind NAT. |
| 7: | Describe some of the features added by IPv6. |
| A7: | Answer:
Plenty of IP addresses are available for the next decades. Multiple levels of hierarchy provide efficient and scalable routing to the Internet. Multihoming with route aggregation. Autoconfiguration allows nodes to configure their IPv6 addresses. A renumbering mechanism provides transparency when customers change IPv6 providers. ARP broadcast is replaced by multicast. The IPv6 header is more efficient than IPv4 Fewer fields A Flow Label field for traffic differentiation New extension headers replace IPv4's Options field Mobility and security mechanisms are built into IPv6. Transition mechanisms help networks move from IPv4 to IPv6. |
| 8: | What is the size in bits of an IPv6 address? |
| A8: | Answer: An IPv6 address has 128 bits. This is 4 times more bits than in IPv4 addresses. |
| 9: | Comparing the OSI reference model of IPv4 to that of IPv6, which layer is updated? |
| A9: | Answer: IPv6 has a change at Layer 3 (the network layer). Upper and lower layers are lightly modified to handle IPv6. |
| 10: | With plenty of IP addresses with IPv6, what is not desirable to have? |
| A10: | Answer: NAT is undesirable in IPv6. |
| 11: | Define aggregation. |
| A11: | Answer: Aggregation is a synonym for route summarization, which is a consolidation of routes in a routing table. The main benefit of aggregation is the reduction of routes in a routing table. |
| 12: | What happens when a customer changes IPv6 providers? |
| A12: | Answer: IPv6 space allocated to a customer is part of the ISP's IPv6 space. To keep a strict aggregation in IPv6, which is desirable for the Internet global routing table, the customer must change its IPv6 prefixes each time it changes providers. |
| 13: | Why is multihoming more interesting with IPv6 than with IPv4? |
| A13: | Answer: Multihoming is possible in both IPv4 and IPv6. But in IPv6, multihoming is made possible by keeping strict route aggregation in the Internet global routing table. |
| 14: | Explain autoconfiguration. |
| A14: | Answer: A router on the local link sends network information to all nodes. Nodes listen to this information and can configure their own IPv6 addresses. |
| 15: | Besides autoconfiguration, name the other methods used to configure IPv6 addresses on nodes. |
| A15: | Answer:
Static configuration (manually), DHCPv6, using random interface identifiers |
| 16: | Describe the disadvantages of ARP broadcast in IPv4. |
| A16: | Answer: ARP broadcast requests cause many interrupts in every node connected on a local link. An ARP broadcast is sent to the IP stack through the interface and the operating system. |
| 17: | List the main change in the IPv6 header compared to IPv4. |
| A17: | Answer:
The IPv4 packet length is 20 bytes compared to 40 bytes for IPv6. Fewer fields are present in the IPv6 header. The IPv4 Header Checksum field is removed. Fragmentation is handled differently in IPv6, so fields related to the fragmentation are either gone or are replaced by extension headers. The Flow Label field is added for traffic differentiation. The IPv4 header Options field is replaced by several extension headers. |
| 18: | What is the purpose of an extension header? |
| A18: | Answer: It provides better efficiency in the options processing, because each extension header ensures that routers and nodes compute only headers targeted for them. |
| 19: | List and define two mechanisms that are embedded in the IPv6 protocol but that are considered add-ons with IPv4. |
| A19: | Answer:
Mobile IP lets nodes move from one IP network to another while keeping the same IP addresses. IPSec enables end-to-end security over IP networks. |
| 20: | How is the migration from IPv4 to IPv6 different from the Y2K bug? |
| A20: | Answer: The Y2K bug was a major shift scheduled for a specific date. The migration from IPv4 to IPv6 will be a smooth transition over several years. |