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.

Internet Architecture

The topic on this entry is how the Internet is structured: the main actors, organizations implied in Internet architecture and the problem with IPv4.

Internet is a global system of interconnected computer networks that use the TCP/IP suite protocol to connect users and applications, and the way to access the net is through an ISP. Them provide connectivity to the users, corporative networks and others Internet Service Provider.

The Internet Assigned Numbers Authority (IANA) is responsible for the global coordination of the Internet Domains, Number Resources and Protocol Assignments. In other words, is the responsible of making the Internet works correctly without centralizing the Internet control. IANA is divided in Regional, National and Local Internet Registries in order to solve the legislation of the different countries. The RIR, which are distributed in continents, manage the distribution of IPv4 and IPv6 address blocks and AS number to the LIR, which are the ISP, that assign  these resources to the end users.

An Autonomous System is a group of IP networks run by one or more networks operators with a single, clearly defined routing policy. So, all the ISP must be in an AS and have an AS number assigned. The relationships between these networks are generally separated in:

• Transit: you pay to another network for Internet access.
• Peer: two networks exchange traffic between each other's customers freely, and for mutual benefit.
• Customer: another networks pay you to provide them with Internet access.

The Internet Service Providers are organized in three levels:

• Tier 1: also called Default Free Zone, which is a network that can reach every other network on the Internet without purchasing IP transit, and without costs.  
• Tier 2: a network that peers with some networks, but still purchases IP transit to reach at least some portion of the Internet. They are the ISP which are to provide access to Internet to a region. 
• Tier 3: a network that solely purchases transit from other networks to reach the Internet. They are the local providers.

On the actual Internet the main kind of network are peer-networks, so normally, the connections are going to be between Tier 3-ISP, and to avoid travelling through the three ISP levels has been created the Internet eXchange Point. It consists in routing Tier 2 or 3 ISP instead of going to an international connection (Tier 1). Some companies refuse it because it is complicated to manage the traffic and charge taxes to the end-user.

Another way to organize the ISP is based on what is offered to the user: services or content. The Content Service Providers are also divided into three groups:

• Network Operator Content Networks: the operator stores content in caches in order to offer better access services. 
• User Content Networks: such as peer-to-peer networks, which store content in a local network.
• Content Providers Content Networks: are divided in Farm servers, which store content in local networks, Mirrors, distributed servers in geographical localizations, but the user has to choose the server, and Content Distribution Networks, distributed servers, just as Mirrors, but with a dynamic pointing.

The CDN networks, are networks based in the idea of joining the users and the content, and shorting the delivery path via global networks of strategically placed servers. This kind of networks are capable of managing and maintaining the networks' elements that deliver Web content, and also provide to value added services, such as customization and adaptation of content, virus scanning and ad insertion. Thereby, these networks achieve reduced latency, high scalability and high availability. 

On Monday 4th, we have talked about how the Internet network is going to be on the next years, and the main requirements which the users are going to request. The three principal topics are: velocity, mobility and security. In terms of providers, there are other requirements that must be solved: the reliability of the net, it is very complex to manage the whole network because the number of ISP has increased in the last years, and the accountability of the net.

The engineers are working in two different ways to provide all of this services: on one hand, they are trying to re-use the existing network and introducing slight changes, and in the other hand, they are reformulating the principles of the network with ideas that provide all of these requirements.

The Content Centric Network is one of these ideas: it consists in identifying the travelling packets so it can be processed in a most efficient way. Recursive Internet Architecture is another idea, is based in the distributed computation and it consist in understanding the net as a single computer and by developing an OS be capable of managing the communication.

The last remarkable idea is the Software Defined Networks: it is an approach to networking in which control is decoupled from the hardware and given to a software application called a controller. The controller is capable of managing the traffic, even blocking specific types of packets, without needing to know the network.

On last Friday we talked about some protocols of the IP Architecture and how it had evolved on the last years.

At first, we spoke about the IP protocol. The IP level is too complex and there are so much protocols to manage, and because of this is really difficult to change or update at the IPv6. Also the appearance of IPv6 created new problems, i.e. applications that were using the IP addresses as user identifier have to change at the new 8 addresses.

We also talked about the Transport Control Protocol (TCP), which at first was oriented at non-reliable communications, low link speed and short distances, but has expanded and nowadays is almost the unique protocol used on the transport layer. It consists of the creation of a virtual circuit where all the packets travel, and with a Round Trip Time (RTT) and the Congestion Avoidance Algorithm to control the saturation of the net. Because of this, the network performance depends on the effectiveness of the TCP protocol.

The BGP protocol allows us to exchange routing information and is one of the most important protocols because it stabilizes the net and gives scalability, although it hasn’t been analytic proved.

We also spoke about three other protocols: NAT, IPSEC and MPLS. Those protocols violate the end-to-end principle but are completely necessary to the net. The NAT protocols is responsible of the translation of the addresses between public and private, and has avoided the exhaustion of the IPv4. It is also a first protection of the corporate network. The IPSEC protocol provides us an end-to-end encryption and hides the transport protocols to the ISP. The MPLS protocol is designed to unify the data transport service on circuit commutation networks and packet commutation networks.