Chapter 2

1	IPv6 addresses are 128 bits in length.
2	IPv6 addresses are represented as eight 16-bit hexadecimal segments separated by colons.
3	The two rules for compacting IPv6 addresses are The leading zeroes in any 16-bit segment do not have to be written. Any single, continuous string of one or more 16-bit segments consisting of all zeroes can be represented with a double colon.
4	Using more than one double colon ambiguates the address; the exact length of each string of zeroes cannot be determined.
5	Both addresses are all zeros. ::/0 is the default address, whereas ::/128 is the unspecified address.
6	The part of a unicast IPv6 address that specifies the host is the Interface ID, and it is usually 64 bits in length.
7	The Subnet ID of the unicast IPv6 address is 16 bits long.
8	An IPv6 address beginning with FF80::/10 is a link-local address.
9	This is a global unicast address, identified by the first three bits of 001.
10	An anycast address is an address that represents a service rather than a device, and can therefore appear on more than one device.
11	A multicast address is an address that represents a group of devices rather than a single device.
12	The IPv6 header is 40 bytes in length.
13	The Flow Label field, by labeling individual flows (packets with the same source and destination address and the same source and destination ports) in the header, is intended to allow highly granular load balancing without having to pay a performance penalty from having to look into the packet payload.
14	The IPv6 Next Header field corresponds to the IPv4 Protocol Number field. It is named differently because the value of the field might specify a following protocol header or it might specify an IPv6 extension header.
15	The Hop Limit field corresponds to the IPv4 Time to Live (TTL) field. The name is changed because routers have never decremented the field according to transit time; rather, every transit router decrements the field by 1, marking a hop instead of a transit time.
16	The IPv6 Next Header field is like the IPv4 Protocol Number field in that it is an 8-bit field that can, if the next header is an upper-layer protocol header, specify the protocol number. But it is different from the Protocol Number field in that it can also specify, if the next header is an IPv6 extension header, that header's type number.
17	Extension headers make the IPv6 header more efficient by being specialized to specific functions and only being included when the specific function is used.
18	The Next Header value of ICMPv6 (corresponding to a Protocol Number) is 58.
19	Aside from the use of the Fragment extension header, the significant difference of IPv6 fragmentation from IPv4 fragmentation is that IPv6 routers do not fragment packets. It is up to the originating host to either fragment packets or ensure that no packet it originates is too large.
20	The five ICMPv6 messages used by NDP are Router Solicitation (RS), Router Advertisement (RA), Neighbor Solicitation (NS), Neighbor Advertisement (NA), and Redirect.
21	The M flag, when set, tells hosts to use DHCPv6 to configure its address. The O flag tells hosts to used DHCPv6 to find other link parameters.
22	The Reachable Timer field specifies the time, in milliseconds, that a node should assume a neighbor is reachable after the node has confirmed reachability.
23	The Retransmit Timer field specifies the period, in milliseconds, that a node should wait between successive transmissions of an NS.
24	A Router Lifetime value of 0 in the RA indicates that the originating router should not be added to a host's default router list.
25	The S flag, when set, indicates that the NA was sent in response to an NS. Two-way reachability is confirmed, and a neighbor address changed to Reachable state in the neighbor cache, only if the NA is in response to a solicitation; so the reception of an NA with the S bit cleared, indicating that it is unsolicited, does not change the state of a neighbor cache entry.
26	Stateful address autoconfiguration relies on DHCPv6 to allocate an address to the host. Stateless address autoconfiguration uses RAs to determine a prefix of larger scope than link-local, plus MAC-to-EUI64 conversion, to determine a host's address.
27	MAC-to-EUI64 conversion inserts a value of 0xFFFE in the middle of a MAC address, then flips the U/L bit to 1, to create a 64-bit Interface ID from a 48-bit MAC address.
28	Duplicate address detection must never be performed on an anycast address.
29	The prefix FF02:0:0:0:0:1:FF00::/104 is used for solicited node multicast addresses. It is prepended to the last 24 bits of an address that is being solicited.
30	IPv6 uses the NDP function Neighbor Address Resolution instead of ARP, and a neighbor cache instead of an ARP cache.
31	A privacy address is one in which the Interface ID is randomly generated, and changed both at some regular period and whenever a host acquires a new prefix. It is used in conjunction with an autoconfigured public address to ensure anonymity of the host. The public address is used for reachability, but the private address is used as the source address of any packets the host originates.
32	An Incomplete state indicates that Neighbor Address Resolution for the entry is in progress.
33	A Probe state indicates that an NS has been sent to verify two-way reachability of a Stale entry, but a responding NA has not yet been received.
34	Neighbor Unreachability Detection verifies two-way reachability of a neighbor either by "hints" from an upper-layer protocol that has received an acknowledgment of a sent message, or by actively probing the neighbor with an NS.