2. cnp3-ebook
3. protocols/ipv6
4. English
5. Zen

38 ../../protocols/ipv6.rst:128
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — ``2001:0db8:0:cd30::`` / ``60`` 31/10000 · 31
39 ../../protocols/ipv6.rst:130
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — IPv6 supports unicast, multicast and anycast addresses. An IPv6 unicast address is used to identify one datalink-layer interface on a host. If a host has several datalink layer interfaces (e.g. an Ethernet interface and a WiFi interface), then it needs several IPv6 addresses. In general, an IPv6 unicast address is structured as shown in the figure below. 356/10000 · 356
40 ../../protocols/ipv6.rst:153
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — An IPv6 unicast address is composed of three parts : 52/10000 · 52
41 ../../protocols/ipv6.rst:155
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — A `global routing prefix` that is assigned to the Internet Service Provider that owns this block of addresses 109/10000 · 109
42 ../../protocols/ipv6.rst:156
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — A `subnet identifier` that identifies a customer of the ISP 59/10000 · 59
43 ../../protocols/ipv6.rst:157
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — An `interface identifier` that identifies a particular interface on a host 74/10000 · 74
44 ../../protocols/ipv6.rst:159
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — The subnet identifier plays a key role in the scalability of network layer addressing architecture. An important point to be defined in a network layer protocol is the allocation of the network layer addresses. A naive allocation scheme would be to provide an address to each host when the host is attached to the Internet on a first come first served basis. With this solution, a host in Belgium could have address ``2001:db8::1`` while another host located in Africa would use address ``2001:db8::2``. Unfortunately, this would force all routers on the Internet to maintain one route towards each host. In the network layer, scalability is often a function of the number of routes stored on the router. A network will usually work better if its routers store fewer routes and network administrators usually try to minimize the number of routes that are known by their routers. For this, they often divide their network prefix in smaller blocks. For example, consider a company with three campuses, a large one and two smaller ones. The network administrator would probably divide his block of addresses as follows : 1117/10000 · 1117
45 ../../protocols/ipv6.rst:161
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — the bottom half is used for the large campus 44/10000 · 44
46 ../../protocols/ipv6.rst:162
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — the top half is divided in two smaller blocks, one for each small campus 72/10000 · 72
47 ../../protocols/ipv6.rst:164
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — Inside each campus, the same division can be done, for example on a per building basis, starting from the buildings that host the largest number of nodes, e.g. the company datacenter. In each building, the same division can be done on a per floor basis, ... The advantage of such a hierarchical allocation of the addresses is that the routers in the large campus only need one route to reach a router in the smaller campus. The routers in the large campus would know more routes about the buildings in their campus, but they do not need to know the details of the organization of each smaller campus. 600/10000 · 600
48 ../../protocols/ipv6.rst:166
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — To preserve the scalability of the routing system, it is important to minimize the number of routes that are stored on each router. A router cannot store and maintain one route for each of the almost 1 billion hosts that are connected to today's Internet. Routers should only maintain routes towards blocks of addresses and not towards individual hosts. For this, hosts are grouped in `subnets` based on their location in the network. A typical subnet groups all the hosts that are part of the same enterprise. An enterprise network is usually composed of several LANs interconnected by routers. A small block of addresses from the Enterprise's block is usually assigned to each LAN. 683/10000 · 683
49 ../../protocols/ipv6.rst:168
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — In today's deployments, interface identifiers are always 64 bits wide. This implies that while there are :math:`2^{128}` different IPv6 addresses, they must be grouped in :math:`2^{64}` subnets. This could appear as a waste of resources, however using 64 bits for the host identifier allows IPv6 addresses to be auto-configured and also provides some benefits from a security point of view, as explained in section ICMPv6_. 423/10000 · 423
50 ../../protocols/ipv6.rst:174
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — In practice, there are several types of IPv6 unicast address. Most of the `IPv6 unicast addresses <http://www.iana.org/assignments/ipv6-address-space/ipv6-address-space.xhtml>`_ are allocated in blocks under the responsibility of IANA_. The current IPv6 allocations are part of the `2000::/3` address block. Regional Internet Registries (RIR) such as RIPE_ in Europe, ARIN_ in North-America or AfriNIC in Africa have each received a `block of IPv6 addresses <http://www.iana.org/assignments/ipv6-unicast-address-assignments/ipv6-unicast-address-assignments.xhtml>`_ that they sub-allocate to Internet Service Providers in their region. The ISPs then sub-allocate addresses to their customers. 694/10000 · 694
51 ../../protocols/ipv6.rst:176
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — When considering the allocation of IPv6 addresses, two types of address allocations are often distinguished. The RIRs allocate `provider-independent (PI)` addresses. PI addresses are usually allocated to Internet Service Providers and large companies that are connected to at least two different ISPs [CSP2009]_. Once a PI address block has been allocated to a company, this company can use its address block with the provider of its choice and change its provider at will. Internet Service Providers allocate `provider-aggregatable (PA)` address blocks from their own PI address block to their customers. A company that is connected to only one ISP should only use PA addresses. The drawback of PA addresses is that when a company using a PA address block changes its provider, it needs to change all the addresses that it uses. This can be a nightmare from an operational perspective and many companies are lobbying to obtain `PI` address blocks even if they are small and connected to a single provider. The typical size of the IPv6 address blocks are : 1056/10000 · 1056
52 ../../protocols/ipv6.rst:178
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — ``/32`` for an Internet Service Provider 40/10000 · 40
53 ../../protocols/ipv6.rst:179
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — ``/48`` for a single company 28/10000 · 28
54 ../../protocols/ipv6.rst:180
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — ``/56`` for small user sites 28/10000 · 28
55 ../../protocols/ipv6.rst:181
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — ``/64`` for a single user (e.g. a home user connected via ADSL) 63/10000 · 63
56 ../../protocols/ipv6.rst:182
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — ``/128`` in the rare case when it is known that no more than one host will be attached 86/10000 · 86
57 ../../protocols/ipv6.rst:189
	English ↹ ↵ NBS … “ ” ‘ ’ ﹙-﹚ ‐ – — There is one difficulty with the utilization of these IPv6 prefixes. Consider Belnet, the Belgian research ISP that has been allocated the ``2001:6a8::/32`` prefix. Universities are connected to Belnet. UCLouvain uses prefix ``2001:6a8:3080::/48`` while the University of Liege uses ``2001:6a8:2d80::/48``. A commercial ISP uses prefix ``2a02:2788::/32``. Both Belnet and the commercial ISP are connected to the global Internet. 429/10000 · 429