4.1 IPv6 Address Types Flashcards
UNICAST
An IPv6 unicast address uniquely identifies an interface on an IPv6-enabled device.
MULTICAST
An IPv6 multicast address is used to send a single IPv6 packet to multiple destinations.
IPv6 does not have a broadcast address. However, there is an IPv6 all-nodes multicast address that essentially gives the same result.
ANYCAST
An IPv6 anycast address is any IPv6 unicast address that can be assigned to multiple devices. A packet sent to an anycast address is routed to the nearest device having that address.
PREFIX LENGHT
In IPv6 it is only called the prefix length (network portion). IPv6 does not use the dotted-decimal subnet mask notation. Like IPv4, the prefix length is represented in slash notation and is used to indicate the network portion of an IPv6 address.
The prefix length can range from 0 to 128. The recommended IPv6 prefix length for LANs and most other types of networks is /64.
The prefix or network portion of the address is 64 bits in length, leaving another 64 bits for the interface ID (host portion) of the address.
It is strongly recommended to use a 64-bit Interface ID for most networks. This is because stateless address autoconfiguration (SLAAC) uses 64 bits for the Interface ID. It also makes subnetting easier to create and manage.
An IPv6 unicast address uniquely identifies an interface on an IPv6-enabled device. A packet sent to a unicast address is received by the interface which is assigned that address. Similar to IPv4, a source IPv6 address must be a unicast address. The destination IPv6 address can be either a unicast or a multicast address.
IPv6 addresses typically have two unicast addresses:
Global Unicast Address (GUA)
This is similar to a public IPv4 address. These are globally unique, internet-routable addresses. GUAs can be configured statically or assigned dynamically.
Link-Local Address (LLA)
This is required for every IPv6-enabled device. LLAs are used to communicate with other devices on the same local link. With IPv6, the term link refers to a subnet. LLAs are confined to a single link. Their uniqueness must only be confirmed on that link because they are not routable beyond the link. In other words, routers will not forward packets with a link-local source or destination address.
Unique local addresses (range fc00::/7 to fdff::/7) are not yet commonly implemented. Therefore, this module only covers GUA and LLA configuration. However, unique local addresses may eventually be used to address devices that should not be accessible from the outside, such as internal servers and printers.
The IPv6 unique local addresses have some similarity to RFC 1918 private addresses for IPv4, but there are significant differences:
Unique local addresses are used for local addressing within a site or between a limited number of sites.
Unique local addresses can be used for devices that will never need to access another network.
Unique local addresses are not globally routed or translated to a global IPv6 address.
Note: Many sites also use the private nature of RFC 1918 addresses to attempt to secure or hide their network from potential security risks. However, this was never the intended use of these technologies, and the IETF has always recommended that sites take the proper security precautions on their internet-facing router.
IPV6 GUA
IPv6 global unicast addresses (GUAs) are globally unique and routable on the IPv6 internet. These addresses are equivalent to public IPv4 addresses. The Internet Committee for Assigned Names and Numbers (ICANN), the operator for Internet Assigned Numbers Authority (IANA), allocates IPv6 address blocks to the five RIRs. Currently, only GUAs with the first three bits of 001 or 2000::/3 are being assigned.
A GUA has three parts:
Global Routing Prefix
Subnet ID
Interface ID
GLOBAL ROUTING PREFIX
The global routing prefix is the prefix, or network, portion of the address that is assigned by the provider, such as an ISP, to a customer or site.
SUBNET ID
The subnet ID field is the area between the global routing prefix and the interface ID. Unlike IPv4 where you must borrow bits from the host portion to create subnets, IPv6 was designed with subnetting in mind. The subnet ID is used by an organization to identify subnets within its site. The larger the subnet ID, the more subnets available.
Note: Many organizations are receiving a /32 global routing prefix. Using the recommended /64 prefix in order to create a 64-bit interface ID, leaves a 32 bit subnet ID. This means an organization with a /32 global routing prefix and a 32-bit subnet ID will have 4.3 billion subnets, each with 18 quintillion devices per subnet. That is as many subnets as there are public IPv4 addresses!
INTERFACE ID
The IPv6 interface ID is equivalent to the host portion of an IPv4 address. The term interface ID is used because a single host may have multiple interfaces, each having one or more IPv6 addresses.
A /64 subnet or prefix (global routing prefix + subnet ID) leaves 64 bits for the interface ID. This is recommended to allow SLAAC-enabled devices to create their own 64-bit interface ID. It also makes developing an IPv6 addressing plan simple and effective.
Note: Unlike IPv4, in IPv6, the all-0s and all-1s host addresses can be assigned to a device. The all-1s address can be used because broadcast addresses are not used within IPv6. The all-0s address can also be used, but is reserved as a subnet-router anycast address, and should be assigned only to routers.
IPv6 LLA
An IPv6 link-local address (LLA) enables a device to communicate with other IPv6-enabled devices on the same link and only on that link (subnet). Packets with a source or destination LLA cannot be routed beyond the link from which the packet originated.
The GUA is not a requirement. However, every IPv6-enabled network interface must have an LLA.
If an LLA is not configured manually on an interface, the device will automatically create its own without communicating with a DHCP server. IPv6-enabled hosts create an IPv6 LLA even if the device has not been assigned a global unicast IPv6 address. This allows IPv6-enabled devices to communicate with other IPv6-enabled devices on the same subnet. This includes communication with the default gateway (router).
Note: Typically, it is the LLA of the router, and not the GUA, that is used as the default gateway for other devices on the link.
There are two ways that a device can obtain an LLA:
Statically - This means the device has been manually configured.
Dynamically - This means the device creates its own interface ID by using randomly generated values or using the Extended Unique Identifier (EUI) method, which uses the client media access control (MAC) address along with additional bits.
