W&L Page 1 CCNA CCNA Training 3.5 Describe IPv6 addresses Jose Luis Flores / Amel Walkinshaw Aug, 2015

W&L Page 2 CCNA IP Addressing (IPv4/IPv6) 3.5 Describe IPv6 addresses 3.5.a global unicast 3.5.b multicast 3.5.c link local 3.5.d unique local 3.5.e eui f auto-configuration

W&L Page 3 CCNA IP Addressing (IPv4/IPv6)

W&L Page 4 CCNA IP Addressing (IPv4/IPv6) Unicast addresses You know unicast addresses from IPv4. A unicast address is the most common form of an IP address and is assigned to one network interface. Multicast addresses Multicast addresses are also known in IPv4. These addresses identify multiple network interfaces / hosts. A typical use of multicast addresses in a Windows environment is the deployment of OS images to multiple hosts, simultaneously. Anycast addresses This is a new address type in IPv6. Like a multicast address, an anycast address identifies multiple interfaces; however, while multicast packets are accepted by multiple machines, anycast packets are delivered only to one interface (host). This address type allows for services that are provided by multiple servers where only one server has to respond. In routing, anycast addresses are used to route packets to the closest routers. And what about broadcast addresses? They no longer exist in IPv6. Broadcasts are replaced by multicast messages. IPv6 knows five different unicast address types: global unicast addresses, link-local addresses, site-local addresses, unique local IPv6 unicast addresses, and special addresses.

W&L Page 5 CCNA IP Addressing (IPv4/IPv6) As you already know, each IPv6-enabled interface, be it a router or computer's interface, will use two distinct addresses:  link-local (FE80::)  global (2000::) Currently there are two global prefixes in use:  global addresses  to4 tunnel (without actually creating a tunnel interface).

W&L Page 6 CCNA IP Addressing (IPv4/IPv6) Global unicast addresses A global unicast address is simply what we call a public IP address in IPv4—that is, an IP address that is routed across the whole Internet. You can make out a global unicast address easily: The first three bits are set to 001. Thus, the address prefix of a global IPv6 address is 2000::/3 because is 2000 in hex. However, in the future, the IANA (Internet Assigned Numbers Authority) might delegate currently unassigned portions of the IPv6 address space. Hence, 2000::/3 won’t always be the prefix for global unicast addresses.

W&L Page 7 CCNA IP Addressing (IPv4/IPv6) Site-local addresses Site-local addresses are equivalent to private IP addresses in IPv4. The address space reserved for these addresses, which are only routed within an organization and not on the public Internet, is /8, /12, and /16. In IPv6, the first 10 bits of a site-local address are set to , which is why these addresses always begin with FEC0. The following 54 bits are the subnet ID, which you can use in your organization for hierarchical routing, and the last 64 bits are the interface ID, which is the part that has to be unique on a link (local network on which hosts communicate without intervening routers). Thus, the prefix of a site-local address is FEC0::/10.

W&L Page 8 CCNA IP Addressing (IPv4/IPv6) Link-local addresses From IPv4, you might know APIPA (Automatic Private IP Addressing) or AutoNet. Whenever automatic IP configuration through DHCP fails, Windows automatically assigns an autoconfiguration address in the range to , which allows the computer to communicate with other machines on the link. In IPv6, link-local addresses always begin with (FE80). Unlike site-local addresses, link-local addresses are never forwarded by routers and therefore can only be reached on the link. This is the reason why the next 54 bits are set to 0. The last 64 bits are set randomly by the operating system. There is an important difference between IPv6 link-local addresses and IPv4 APIPA addresses. Once a PC receives an IPv4 address from a DHCP server, the APIPA address is no longer reachable. However, with IPv6, a network interface always has a link-local address even if you assign another IPv6 address manually or if the NIC receives an IPv6 address from a DHCP server. This means that computers on a link can always communicate through IPv6 using link-local addresses, which is not the case in IPv4 because APIPA addresses are not in the same subnet as private or public IPv4 addresses. Thus, if the local DHCP is unavailable, the computers can still access local services through IPv6 but won’t be able to reach the Internet or services in other links.

W&L Page 9 CCNA IP Addressing (IPv4/IPv6) ipv6 address link-local To configure an IPv6 link-local address for an interface and enable IPv6 processing on the interface, use the ipv6 address link-localcommand in interface configuration mode. To remove the address from the interface, use the no form of this command. ipv6 address ipv6-address/prefix-length link-local [cga] no ipv6 address [ ipv6-address/prefix-length link-local ]

W&L Page 10 CCNA IP Addressing (IPv4/IPv6) IPv6 zone ID The purpose of zone IDs is to distinguish these addresses. For instance, if host A has two NICs that are connected to two different links (subnets), the same local-link address could have been used for NIC 1 on host A and on host B that is on the link of host A’s NIC 2. To distinguish this ambiguous link-local address, host A uses the interface index of NIC 1 as the zone ID for the local IP address. For site-local addresses, the operating system uses the site ID (also called the scope ID). If a host is only connected to one site, this ID is always 1. You can display the interface indexes on a host with the command “netsh interface ipv6 show address level=verbose”. If you launch the ipconfig command, you can see the local-link and site-local addresses with their zone IDs. The syntax for identifying the zone is address%zone_ID. This is an example of a link-local IP address with zone ID 11: fe80::bd0f:a8bc:6480:238b%11. Note that the zone ID is only known at the local host that assigned it. I think in practice you will seldom be bothered with zone IDs as you don’t have to configure them manually.

W&L Page 11 CCNA IP Addressing (IPv4/IPv6) Unique local IPv6 unicast address Even with the use of zone IDs, you should probably avoid having ambiguous IP addresses in your network. Instead of site-local addresses, you can work with unique local IPv6 unicast addresses. These local-use addresses are also not routed across the Internet; however, like global IPv6 addresses, they are unique. Well, more or less, as you will soon see. The prefix of unique local IPv6 unicast addresses is FC00::/7. The eighth bit is the Local flag and is set to 1 for local addresses. A Local flag with 0 has not yet been defined. Perhaps this could be a way to make local IPv6 addresses global? Anyway, until IPv6, creators have made up their mind, the prefix of unique local IPv6 unicast addresses is FD00::/8. Don’t worry if you don’t really understand this; all you really have to know about unique local IPv6 unicast addresses is this: The next 40 bits are for the global ID and are randomly set. The following 16 bits are the subnet ID, which you can use for hierarchical addresses within your organization. As usual, the last 64 bits are the interface ID.

W&L Page 12 CCNA IP Addressing (IPv4/IPv6) ipv6 address eui-64 To configure an IPv6 address for an interface and enables IPv6 processing on the interface using an EUI-64 interface ID in the low order 64 bits of the address, use the ipv6 address eui-64command in interface configuration mode. To remove the address from the interface, use the no form of this command. ipv6 address ipv6-prefix/prefix-length eui-64 no ipv6 address [ ip v6-prefix/prefix-length eui-64 ]

W&L Page 13 CCNA IP Addressing (IPv4/IPv6) ipv6 address autoconfig To enable automatic configuration of IPv6 addresses using stateless autoconfiguration on an interface and enable IPv6 processing on the interface, use the ipv6 address autoconfig command in interface configuration mode. To remove the address from the interface, use the no form of this command. ipv6 address autoconfig [default] no ipv6 address autoconfig

W&L Page 14 CCNA IP Addressing (IPv4/IPv6) What is known as "one-to-nearest" addressing in IPv6? A. global unicast B. anycast C. multicast D. unspecified address Explanation: IPv6 Anycast addresses are used for one-to-nearest communication, meaning an Anycast address is used by a device to send data to one specific recipient (interface) that is the closest out of a group of recipients (interfaces).

W&L Page 15 CCNA IP Addressing (IPv4/IPv6) Which two of these statements are true of IPv6 address representation? (Choose two.) A. There are four types of IPv6 addresses: unicast, multicast, anycast, and broadcast. B. A single interface may be assigned multiple IPv6 addresses of any type. C. Every IPv6 interface contains at least one loopback address. D. The first 64 bits represent the dynamically created interface ID. E. Leading zeros in an IPv6 16 bit hexadecimal field are mandatory.

W&L Page 16 CCNA IP Addressing (IPv4/IPv6) (Simplified) automatic address assignment Much of the documentation talks of “simplified” address assignment, but I somehow think this new feature will cause confusion among admins in the beginning. In an IPv4 network, a computer’s automatic address assignment means that a DHCP server is involved. IPv6 still knows DHCP-based address assignment (also called stateful address configuration), but now hosts can also configure themselves with IPv6 addresses (stateless address configuration). There are two types of stateless configurations. Hosts can derive an IP address from a prefix (the first part of an IPv6 address that belongs to your organization) advertised by a local router, and they can assign themselves so-called link- local addresses (addresses that are not routed), which they can use to communicate with other nodes on the link (local network).

W&L Page 17 CCNA IP Addressing (IPv4/IPv6) Neighbor discovery The Internet Control Message Protocol for IPv6 (ICMPv6) will replace the Address Resolution Protocol (ARP). You probably know that ARP is used to determine the link layer address (MAC address in the case of Ethernet) from the IP address. The main problem of ARP is that it uses broadcasts, which disturbs all hosts on the link (LAN). By contrast, IPv6 uses Neighbor Solicitation multicast messages for neighbor discovery. Instead of sending a broadcast message to all nodes on the link, only the so-called solicited node multicast IPv6 address is contacted. The first 104 bits of the solicited node multicast are fixed (FF02::1:FF00:0/104), and the last 24 bits are equivalent to the last 24 bits of the IP address that has to be resolved. Since only nodes that share the last 24 bits in their IP address will listen to the solicited node address, fewer hosts are disturbed.

W&L Page 18 CCNA IP Addressing (IPv4/IPv6) Extensibility While the IPv4 header only supports 40 bytes for options, the size of the IPv6 extensions is only constrained by the size of the IPv6 packet. IPv6 supports multiple so- called extensions headers that can be added after the IPv6 header. These extensions headers have no maximum size, which makes future enhancements of the protocol quite flexible.

W&L Page 19 CCNA Bibliography

W&L Page 20 CCNA Q&A