IP ADDRESS

                  

What is an IP Address....?

• An IP address is a unique global address for a network interface

• Exceptions:

– Dynamically assigned IP addresses ( DHCP)

– IP addresses in private networks ( NAT)

• An IP address:

- is  a 32 bit long identifier

- encodes a network number (network prefix) and a host number

Network prefix and host number

• The network prefix identifies a network and the host number identifies a specific host (actually, interface on the network).

• How do we know how long the network prefix is?

– Before 1993: The network prefix is implicitly defined (seeclass-based addressing)or

– After 1993: The network prefix is indicated by a netmask.

Dotted Decimal Notation

• IP addresses are written in a so-called dotted decimal notation

• Each byte is identified by a decimal number in the range [0..255]:

• Example:

• Example: example.ab.demo.edu

• Network address is:  128.143.0.0   (or 128.143)

• Host number is:  137.144

• Netmask is:  255.255.0.0 (or   ffff0000)

• Prefix or CIDR notation: 128.143.137.144/16

» Network prefix  is 16 bits long

 Special IP Addresses

1. Reserved or (by convention) special addresses:

Loopback interfaces

– all addresses 127.0.0.1-127.0.0.255 are reserved for loopback interfaces

– Most systems use 127.0.0.1 as loopback address

– loopback interface is associated with name “localhost”

IP address of a network

– Host number is set to all zeros, e.g., 128.143.0.0

Broadcast address

– Host number is all ones, e.g., 128.143.255.255

– Broadcast goes to all hosts on the network

– Often ignored due to security concerns

2. Test / Experimental addresses

Certain address ranges are reserved for “experimental use”. Packets should get dropped if they contain this destination address (see RFC 1918):

10.0.0.0 - 10.255.255.255

172.16.0.0 - 172.31.255.255

192.168.0.0 - 192.168.255.255

3. Convention (but not a reserved address)

Default gateway has host number set to ‘1’, e.g., e.g., 192.0.1.1

Subnetting

·        Grouping the network

·        Used in IP network to break up larger networks into smaller network

·         Reduced network traffic

·         Optimized network performance

·         Simplify management and monitoring

·         Easly identify and isolating network problems

Supernetting

·        It refers to increase host and reduce the subnets

·        Reduce the network bits and increase the host bits

Address assignment with subnetting

• Each part of the organization is allocated a range of IP addresses (subnets or subnetworks)

• Addresses in each subnet can be administered locally

Basic Idea of Subnetting

• Split the host number portion of an IP address into a subnet number and a (smaller) host number.

• Result is a 3-layer hierarchy

• Then:

• Subnets can be freely assigned within the organization

• Internally, subnets are treated as separate networks

• Subnet structure is not visible outside the organization

Subnetmask

• Routers and hosts use an extended network prefix(subnetmask) to identify the start of the host numbers

Example: Subnetmask

• 128.143.0.0/16 is the IP address of the network.

• 128.143.137.0/24 is the IP address of the subnet.

• 128.143.137.144  is the IP address of the host.

• 255.255.255.0 (or ffffff00) is the subnetmask of the host.

• When subnetting is used, one generally speaks of a “subnetmask”

(instead of a netmask) and a “subnet” (instead of a network).

• Use of subnetting or length of the subnetmask if decided by the network administrator.

• Consistency of subnetmasks is responsibility of administrator.

NO SUBNETTING             

WITH SUBNETTING

           

Classful IP Adresses

• When Internet addresses were standardized (early 1980s),

the Internet address space was divided up into classes:

– Class A: Network prefix is 8 bits long

– Class B: Network prefix is 16 bits long

– Class C: Network prefix is 24 bits long

• Each IP address contained a key which identifies the class:

– Class A: IP address starts with “0”

– Class B: IP address starts with “10”

– Class C: IP address starts with “110

CIDR - Classless Interdomain Routing

• IP backbone routers have one routing table entry for each network address:

– With subnetting, a backbone router only needs to know one entry for

each Class A, B, or C networks

– This is acceptable for Class A and Class B networks

• Consequence: The Class-based assignment of IP addresses

had to be abandoned

CIDR:-

• Goals:

– New interpretation of the IP address space

– Restructure IP address assignments to increase efficiency

– Permits route aggregation to minimize route table entries

• CIDR (Classless Interdomain routing)

– abandons the notion of classes

– Key Concept: The length of the network prefix in the IP addresses is

        kept arbitrary

         – Consequence: Size of the network prefix must be provided with an IP                          

                  Address.

IPv6 - IP Version 6

• IP Version 6

– Is the successor to the currently used IPv4

– Specification completed in 1994

– Makes improvements to IPv4 (no revolutionary changes)

• One (not the only !) feature of IPv6 is a significant increase in of the IP address to 128 bits (16 bytes)

• IPv6 will solve – for the foreseeable future – the problems with IP addressing.

IPv6 Header

IPv6 vs. IPv4: Address Comparison

IPv6 Provider-Based Addresses

• The first IPv6 addresses will be allocated to a provider-based plan

• Type: Set to “010” for provider-based addresses

• Registry: identifies the agency that registered the address

  The following fields have a variable length (recommeded length in “()”)

• Provider: Id of Internet access provider (16 bits)

• Subscriber: Id of the organization at provider (24 bits)

• Subnetwork: Id of subnet within organization (32 bits)

• Interface: identifies an interface at a node (48 bits)

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