1、Internet Addressing A Technical Overview,David R. Conrad drcisc.org Internet Software Consortium,Overview,Background Internet Address History Internet Address Allocators Conclusions,Addresses - How to get here from there,Addresses provide information on how to locate something, e.g., what route to t
2、ake from here to there. Internet addresses combine a routing portion, known as the network part a name portion known as the host part How to split an Internet address into the network part and the host part has changed over time,The Beginning,Back when the TCP/IP protocols were first being designed,
3、 there was a big argument between fixed length and variable length addresses Fixed length will always be limited But if you make it big enough, no one will notice Variable length will always take more cycles to process But there are tricks you can play to minimize the difference The decision was mad
4、e for fixed, 32 bit addresses Rumor has it, by a flip of a coin.,IP version 4 Addresses,32 bit unsigned integers possible values 0 - 4,294,967,295 Typically written as a “dotted quad of octets” four 8 bit values with a range of 0-255 separated by “.” For example, 202.12.28.129 can be written as belo
5、w,Internet Addresses,A subset of IPv4 addresses One of an infinite number Guaranteed globally unique by the IANA Generally allocated by delegated authorities such as Internet service providers or regional registries Assumed to be routable Bad assumption Partitioned into two parts A host part that id
6、entifies a particular machine on a local or wide area network A network part that gives routers information how to get to the local or wide area network via the Internet,Internet Address Structure,Originally, the architects of the Internet thought 256 networks would be more than enough Assumed a few
7、 very large (16,777,216 hosts) networks They were wrong (in case you were wondering) Addresses were partitioned as below 8 bit network part, 24 bit host part,Classfull Addressing,Original addressing plan too limiting More than 256 networks with many fewer hosts than 224 Solution was to create addres
8、s classes,The Problem,Class A way too big 16 million hosts in a flat network is unthinkable Class B too big Even 65536 host addresses is too many in most cases Imagine 65534 hosts all responding to a broadcast Class C too small Most sites initially connecting to the Internet were large Universities,
9、 256 was too small for them Need more flexibility!,Subnetting,Classfull addressing was a better fit than original but class A and B networks impossible to manage Solution was to partition large networks internally into sub-networks (subnets) Typically “class C” (8 bit host part) sized subnets althou
10、gh variable length subnets used too,Classless Addressing,Forget what I just told you Classfull addressing is officially “Bad” 3 sizes just dont fit all - very wasteful Better solution is to use variable length partitioning between the host and network parts Actual partitioning for a site provided by
11、 routing protocol notation is dotted quad followed by a “/” and the network part length, e.g., 202.12.28.129/26 First host on 64 host network starting at 202.12.28.128 No need for subnets,Example of Classless Addressing,Prefix 202.12.28.0/22 1024 host addresses announced as a single network (importa
12、nt!) Consists of 7 subnets 202.12.28.0/25 202.12.28.128/26 202.12.28.192/26 202.12.29.0/24 202.12.30.0/24 202.12.31.0/25 202.12.31.128/25,Summary,Internet addresses are 32 bit fixed length globally unique numbers One subset of all IPv4 address spaces Internet addresses have evolved over time to be more flexible and to include hierarchy Currently, classless addressing is in use providing arbitrary host and network part lengths.,
