mcse 01 network essentials 03 theory

8/6/2019 MCSE 01 Network Essentials 03 Theory

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Assigning IP Addresses in aMultiple Subnet Network


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IP Addressing


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Virtual Networks

Internetworking software builds a single,seamless virtual network out of multiple

physical networks

Universal addressing scheme Universal service

All details of physical networks hidden from

users and application programs


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IP Protocol Objectives

Connect physical networks of every possibletype (even future network technologies notyet developed )

Scale to a WAN connecting many hosts To succeed, IP has to make minimal assumptions

about the physical networks it connects The IP Service Model

Provides a global Addressing Scheme Provides best-effort, connectionless, variable-

length, datagram delivery


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Global Addressing Scheme Specified by Internet Protocol In addition to physical address (contained in NIC), each

host is assigned a 32-bit IP address .


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Internet Addresses

Each interface on the internet must have a unique InternetAddress , or IP address. An IP address is a 32 bit number. Usually written using Dotted Decimal Notation

Example: 2365328673 as an unsigned integer is 1000 1100 1111 1100 0000 1101 0010 0001 in binary 8C FC 0D 21 in hex

140.252.13.33 in dotted decimal


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Dotted Decimal Notation

Syntactic form used by IP software to make the 32-bit formshorter and easier to read Written in decimal form with decimal points separating the

bytes


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Details of IP Addresses

Assigned per interface , not per host, hence... Routers always have multiple IP addresses.

Three kinds of IP Addresses unicast : destined for a single host

broadcast : destined for all hosts on a local net(not all hosts on the internet)

multicast :destined for all hosts in a specific multicast group .

(We will concentrate for now on unicast addresses)


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Classes of IP Addresses

0

Class

A

E 1 1 1 1 0

D 1 1 1 0

B 1 0

01C 1

netid hostid7 bits 24 bits

14 bits 16 bits

21 bits8 bits

28 bits

27 bits

netid hostid

netid hostid

multicast group id

(reserved for future use)A: 0.0.0.0 to 127.255.255.255B: 128.0.0.0 to 191.255.255.255C: 192.0.0.0 to 239.255.255.255

D: 224.0.0.0 to 239.255.255.255E: 224.0.0.0 to 247.255.255.255


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Decimal representation and class ranges of Internet addresses


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Details of IP Addresses Assigned by a central authority

the Network Information Center, or InterNIC (rs.internic.net)assigns network ids for the entire internet.

Local system administrator gets a network id from the InterNIC,then assigned Ids to individual interfaces on each host.

The hostid portion may be broken down by a local system

administrator into subnet and host. Special case addresses:


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Network and Host Addresses


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Summary of special IP addresses

Prefix Suffix Type of Address Purpose

All 0s All 0s This computer Used during bootstrap Network All 0s Network Identifies a network Network All 1s Directed broadcast broadcast on specified netAll 1s All 1s limited broadcast broadcast on local net127 Any loop back testing


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Domain Name System

The network interface and hosts are known to the protocols by their IPaddresses, e.g. 128.175.201.5

Humans work better with hostnames, such as gloin.cis.udel.edu or brahms.udel.edu

Domain Name System (DNS):a distributed database for mapping between hostnames and IP addresses.

Details not in this discussion; it suffices that there is a library function wecan call to translate.

gethostbyname()

gethostbyaddr()

Most applications accept either one.

128.175.201.5DNSgloin.cis.udel.edu


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Routers and IP addresses

An internet is composed of arbitrarily many physicalnetworks interconnected by routers Each IP address specifies only one physical network.

What is the routers address?

Routers can have more than two interfaces, therefore must be assigned one IP address for each connection.

An IP address identifies a connection between a computer

and a network, not a specific computer.


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Routers


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The IP address shortage

The problem: almost all class B addresses have already been allocated. 32 bit addresses are inadequate for the predicted growth of the

internet. Routing table growth

Current Routing Structure is not hierarchical; there are only twolayers (network, host).

As multiple C class addresses are given out instead of a singleclass B address for each network, routing tables will get too large

The solution: short term:

Subnetting Classless Interdomain Routing (CIDR) addresses routing table

growth problem long term: IPv6 (128-bit addresses)


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Subnetting IP addressing has only two levels of hierarchy

Subnetting - Add another level to address/routing hierarchy:subnetworks


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Subnetting 3 levels of hierarchy: Netid, subnetid, hostid

Subnets are visible only within the local site Masking : process that extracts address of physical network

from an IP address. Subnet masks define variable partition of host part of Class

A and B addresses

Network Number SubnetID HostID

Subnetted Address

Class B Address

Subnet Mask (255.255.255.0)00000000111111111111111111111111


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MaskingTo find network or subnetwork address, apply (perform AND)

the mask to the IP address


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Finding the Subnet Address

Given an IP address, we can find thesubnet address the same way we found thenetwork address in the previous chapter.

We apply the mask to the address. We cando this in two ways: straight or short-cut.


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Straight Method

In the straight method, we use binarynotation for both the address and themask and then apply the AND operationto find the subnet address.


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Example 1 Example 1

What is the subnetwork address if thedestination address is 200.45.34.56 and thesubnet mask is 255.255.240.0?


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Solution Solution

11001000 00101101 00100010 00111000

11111111 11111111 1111 0000 00000000

11001000 00101101 0010 00000000 0000000000000000

The subnetwork address is 200.45.32.0 .


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Short-Cut Method

** If the byte in the mask is 255, copythe byte in the address.

** If the byte in the mask is 0, replacethe byte in the address with 0.

** If the byte in the mask is neither 255nor 0, we write the mask and the addressin binary and apply the AND operation.


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Example 2 Example 2

What is the subnetwork address if the

destination address is 19.30.80.5 and themask is 255.255.192.0?

Solution Solution

See Figure 5.6


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Example 2

Figure 5-6


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Figure 5-7

Comparison of a default mask anda subnet mask


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The number of subnets must beThe number of subnets must be a power of 2. a power of 2.


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Example 3 Example 3A company is granted the site address201.70.64.0 (class C). The company needssix subnets. Design the subnets.

Solution Solution

The number of 1s in the defaultmask is 24 (class C).


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Solution (Continued) Solution (Continued)The company needs six subnets. This number6 is not a power of 2. The next number that isa power of 2 is 8 (2 3). We need 3 more 1s inthe subnet mask. The total number of 1s inthe subnet mask is 27 (24 + 3).

The total number of 0s is 5 (32 27). Themask is


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Solution (Continued) Solution (Continued)

11111111 11111111 11111111 111 00000or

255.255.255.224

The number of subnets is 8.The number of addresses in each subnetis 2 5 (5 is the number of 0s) or 32.


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Example 3


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The company needs 1000 subnets. Thisnumber is not a power of 2. The next numberthat is a power of 2 is 1024 (2 10 ). We need 10more 1s in the subnet mask.

The total number of 1s in the subnet mask is26 (16 + 10).The total number of 0s is 6 (32 26).


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The mask is 11111111 11111111 11111111 11000000

or255.255.255.192.

The number of subnets is 1024.The number of addresses in each subnet is 2 6 (6 is the number of 0s) or 64.


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