CISSP PRACTICE QUESTIONS – 20210305

You are learning about IPv6 addressing. Which of the following is not correct?
A. There are no broadcast addresses in IPv6.
B. IPv6 nodes boot with the default address (::0) and use multicast to contact the DHCP server.
C. An anycast must not be used as the source address and can be assigned only to a router.
D. A link-local address is automatically configured using the prefix FE80::/10 and the modified EUI-64 format.

Kindly be reminded that the suggested answer is for your reference only. It doesn’t matter whether you have the right or wrong answer. What really matters is your reasoning process and justifications.

My suggested answer is B. IPv6 nodes boot with the default address (::0) and use multicast to contact the DHCP server.

Pv6 nodes boot with a local-link address (with the prefix FE80::/10) and use multicast to contact the DHCP server. They are different from IPv4 hosts, which boot with a default address (0.0.0.0) and use broadcast (DHCP Discover) to contact the DHCP server.

DHCPv4 Operations (Source: WizNet)

A link-local address is automatically configured using the prefix FE80::/10 and the modified EUI-64 format.

48-bit MAC to 64-bit EUI-64 address (Source: StackExchange)
Structure of a 48-bit MAC address (Source: Wikipedia)

The following is an excerpt from IBM IPv6 Introduction and Configuration:

The IPv6 address protocol is specified in RFC 4291 – IPv6 Address Architecture. IPv6 uses a 128-bit address instead of the 32-bit address of IPv4. It defines three major types of addresses: unicast address, multicast address, and anycast address. There are no broadcast addresses in IPv6.

Unicast Address

A unicast address is an identifier assigned to a single interface. Packets sent to that address
are delivered only to that interface. Special purpose unicast addresses are defined as follows:
– Loopback address (::1)
– Unspecified address (::)
– Link-local address
– Site-local address
– IPv4-compatible address (::)
– IPv4-mapped address (::FFFF:)

Multicast Address

A multicast address is an identifier assigned to a set of interfaces on multiple hosts. Packets
sent to that address are delivered to all interfaces corresponding to that address. There are
no broadcast addresses in IPv6, their function being superseded by multicast addresses.
4-bit value that indicates the scope of the multicast. Possible values are:
0 Reserved.
1 Confined to interfaces on the local node (node-local).
2 Confined to nodes on the local link (link-local).
5 Confined to the local site.
8 Confined to the organization.
E Global scope.
F Reserved.

Anycast Address

An anycast address is a special type of unicast address that is assigned to interfaces on
multiple hosts. Packets sent to such an address are delivered to the nearest interface with
that address. Routers determine the nearest interface based upon their definition of distance, for example, hops in case of RIP or link state in case of OSPF.
Anycast addresses use the same format as unicast addresses and are indistinguishable from them.
RFC 4291 – IPv6 Address Architecture currently specifies the following restrictions on
anycast addresses:
- An anycast address must not be used as the source address of a packet.
- Any anycast address can be assigned only to a router.

Reference

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您正在學習IPv6定址。 以下哪項是不正確的?
A. IPv6中沒有廣播地址。
B. IPv6節點開機時使用預設位址(:: 0)並以群播(multicast)與DHCP服務器聯繫。
C. Anycast不能用作來源地址(source address),只能分配給路由器。
D. 本地鏈接(link-local)地址由系統使用前綴(prefix)FE80::/10和EUI-64的改良格式自動配置。

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