UCI University of California, Irvine

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1 IP Class-based Addressing All IPv4 addresses have 4 bytes. The first 1, 2, or 3 bytes correspond to the "network", and the remaining bytes correspond to the "host number", with the location of the partition determined by the first 3 bits. (Walrand, fig. 3.9) By convention, IP addresses are written as "byte1.byte2.byte3.byte4". Class-based addressing is not very efficient in use of the address space, e.g. a network with 300 hosts uses up 1 class B address.

2 IP Subnetting: Divide the "host number" portion of the address into "subnet ID" and "host ID", with the partition given by a "subnet mask". (Peterson, fig. 4.24) Network number Host number Class B address Subnet mask ( ) Network number Subnet ID Host ID Subnetted address For instance, if the subnet uses 1 byte and the host uses 1 byte (as pictured), then the IP address is "network.subnet.host".

3 IP Classless Addressing (CIDR): Classless addressing allows for an arbitrary partition between the "network" and the "host number": (Peterson, fig. 4.26) Corporation X ( ) Border gateway (advertises path to ) Regional network Corporation Y ( ) In this example, Corporation X has a classless network address consisting of 20 bits, leaving 12 bits for the "host number". This is the equivalent of 16 class C addresses. Notation: Corp X s "network prefix" is written as /20, where the 20 indicates the number of bits in the prefix.

4 P Classless Addressing (CIDR): CIDR also allows routers to reduce the size of routing tables, since they can contain 1 entry for multiple networks. Corporation X ( ) Border gateway (advertises path to ) Regional network Corporation Y ( ) Corp X s network prefix is /20 and Corp Y s network prefix is /20. Rather than using 2 separate routing tables entries for Corp. X and Corp. Y, routers can use a single entry /14.

5 IP addresses and domain names are managed by Internet registries. Names are written as hostname.subdomain.domain, with an abitrary number of subdomains, thus forming a tree. (Peterson, fig. 9.3) edu com gov mil org net uk fr princeton mit cisco yahoo nasa nsf arpa navy acm ieee cs ee physics ux01 ux04

6 The translation from name to IP address is done by the Domain Name System. Each subdomain and domain has a. Together, these s act as a distributed database. The highest level s are known as "root s". (Peterson, fig. 9.4) Root Princeton Cisco CS EE

7 A query to learn the IP address corresponding to a name goes through a sequence of s: (Peterson, fig. 9.5) Client 1 cicada.cs.princeton.edu Local name server cicada.cs.princeton.edu princeton.edu, cicada.cs.princeton.edu cs.princeton.edu, Root name server Princeton name server cicada.cs.princeton.edu 6 cicada.cs.princeton.edu, CS name server

8 Queries to DNS are made in either a "non-recursive" manner or in a "recursive" manner. Non-recursive query: steps 1-8 below. Recursive query: A -> C -> root -> D -> E -> D -> root -> C -> A. (Walrand, fig. 3.8)

9 The result of a query is one or more database records including the IP address of the desired host. It may also include an alias for the indicated host, and/or the name of a mailserver for the indicated host.