IPv6

In today’s entry, we are going to talk about the IPv6 addressing and the transition to it from IPv4. Since the Internet has been working on, the addressing has been organized based on the IPv4 blocks. These addresses blocs are not bought; they are public resources that can be used always that fulfill RIR rules and being a LIR member.

IPv4 addresses are divided into:

• Provider aggregatable: Blocks of addresses that may be sub-assigned to other ISPs or to other companies that also may leased the addresses to their customers
• Provider Independent: Blocks of addresses that cannot be sub-assigned to other ISP and only may be assigned to end users.

Over time, the explosion of Internet provoked problems in the scalability of the Internet architecture: IANA just provides /8 blocks to RIR, which leases subnetting blocks from /8 to ISP. ISP has to deal with multiple users, so NAT is an intermediate solution to delay IP addresses exhaustion. 
Nowadays addresses have been exhausted, and the new IPv6 is being progressively deployed. Its main feature is increasing the number of IPv4 addresses from 32 bits to 128 bits, but also, improves IPv4 address space and deals with security (IPSEC).

IPv6 header has new interesting fields, such as the version of the packet, the type of service or the “new header” field, which consists in indicate if there is an embedded header with options for this packet, i.e. authentication, cryptography, routing...

There are 3 kinds of addresses in IPv6:

• Unicast: addresses pointing to just one destination
• Anycast: addresses pointing to any destination among a group of destinations
• Multicast: addresses pointing to several destinations (includes broadcast).

Another interesting feature of IPv6 addresses is that they have a scope: global addresses which are routed in the whole Internet, site local addresses which are not routed outside the local network, and link local addresses which are not routed by routers.

ICMP has also been modified to ICMPv6, which combines the features of old ICMPv4 with new ones, i.e. neighbor discovery. It is a function that allows:

• Address resolution: it learns L2 addresses from the host (is equivalent to ARP).
• Router discovery: it learns the router which we are connected.
• Agent discovery: especially for mobile IPv6, consists in knowing if the node has moved from one network to another.

Finally, the method to obtain an address is similar to IPv4: the router provides a prefix, which represents the network, and the computer adds an id. To manage all the addressing system, it has been created a DHCP server that will centralize the IP assignments.