subnetting,supernetting, vlsm & cidr - srm university 1(3).pdf · • there are several...

Subnetting,Supernetting, VLSM & CIDR

WHAT - IP Address

Unique 32 or 128 bit Binary, used to identify a system on a Network or Internet.

Network Portion Host Portion

CLASSFULL ADDRESSING

• IP address space is divided into five classes: A, B, C, D, and E.

Network and Host IDs

• Each IP address is divided into two parts– Network part, defined by netid – identifies a network

– Host part, defined by hostid – identifies a host within a network

Class A Address

• Network Bits = 7No.of Networks = 27 – 1 = 127

• Host Bits = 24No.of Host/NW = 224 – 2 = 16 Million

• Range :0.0.0.0 to 127.255.255.255

0 NET HOST HOST HOST

Class B Address

• Network Bits = 14No.of Networks = 214 – 1 = 16,383

• Host Bits = 16No.of Host/NW = 216 – 2 = 65,234

• Range :128.0.0.0 to 191.255.255.255

10 NET NET HOST HOST

Class C Address

• Network Bits = 21No.of Networks = 221 – 1 = 2 Million

• Host Bits = 8No.of Host/NW = 28 – 2 = 254

• Range :192.0.0.0 to 223.255.255.255

110 NET NET NET HOST

Special Purpose IP Addresses

• Private IP Address• Default NW Address• Broadcast Address• Loopback Address

Private IP Addresses

• Private addresses are not recognized globally• Private address often used together with NAT techniques

Other Special Addresses

• There are several addresses within each class that are reserved for such special purposes as broadcast.

Direct Broadcast

• Direct broadcast sends a message to all the hosts within a specific network. • Direct broadcast address consists of network id followed by all 1s.

Limited Broadcast

• Limited broadcast sends a message to all the hosts within THIS network. • Limited broadcast address consists of all 1s.

This Host on This network

• The network address that consists of all 0s indicates this host on this network.– Used at the bootstrap time when host does not know its IP address.– This address is used as a source address in limited broadcast message to determine its IP

address.– Can only be used as a source address.

Specific Host on This network

• The network address that consists of all 0s for netid and specific value for hostid is destined to a specific host on THIS network– Used a host to send a message to another host on same network.– This address can only be used as destination– Usually class A addresses

Loopback Address

• IP address with first byte value of 127 is used for the loopback address.– Packets with such destination address never leave the machine

• Loopback can be used only as destination address• Loopback is class A address which reduces the number of class A

addresses by 1 block

Loopback address can be used for Testing IP software, Sending a message between

client and server programs located on the same machine, etc

SUBNETTING& NETMASKS

SUBNETTING

WHAT

• Subnetting is dividing a network into several smaller parts (subnets), each having its own sub-network address.

• Traditional Internet uses two-level address hierarchy: netidsand hostids

• Subnetting provides another, third, level of hierarchy.

Network Portion Subnet Portion

Host Portion

SUBNETTING

WHY

More EFFICIENT & STRUCTURED utilization of IP Address

In subnets we use Subnet Mask or NetMask

SUBNET MASK OR NETMASK

WHATA Bit stream of Contiguous ONES & ZEROS

WHYIts used to determine network part of the address for a given IP address.

SUBNET MASK OR NETMASK

TYPES

• Natural / Default Network Mask

• Custom / Subnet Mask

Creating Subnets Using Masks

• WE EXTEND THE NETWORK PORTION INTO HOST

• Mask is a 32‐bit number that consists of – Consecutive 1s indicating bits that belong to the network part of address followed

by

– Consecutive 0s indicating bits that do not belong to network part of the address

Bit-wise AND operation between the IP address and mask results in the network part of the address

Subnet Masks

• Subnet masks operate the same way as default masks.• Unlike default classful masks, subnet masks are required to

identifying the subnetwork.

SUPERNETTING

SUPERNETTING

• Supernetting is combining several small networks (e.g. of class C) into a big one to create a large range of addresses.

Supernetting

• In supernetting, the first address of the supernet and the supernet mask define the range of addresses.

CIDR notation is applicable to suppernetting as well.For example:

201.12.192.3/21Shows that address belongs to supernet of class C networks with mask

255.255.248.0Since 248 = 11111000, 8 class C networks were combined together to create a supernet.

VLSMVariable Length Subnet Mask

VLSM - Purpose

• To increase usability of Subnets

Using classical subnetting the subnets are of same size

Using VLSM the subnets can be of VARIABLE SIZE

VLSM

Eg : a Class C, NW need to be divided into 110,45,50 Hosts?

Available Options 1 :‐

Natural NW Mask‐ Class C is 255.255.255.0

Which will provide nothin but 254 hosts under 1 NW

VLSM


Available Options 2 :‐

The Subnet Mask of the form 255.255.255.X

X (in Binary) X No of Subnets No of Hosts

1000 0000 128 2 128

1100 0000 192 4 64

1110 0000 224 8 32

1111 0000 240 16 16

1111 1000 248 32 8

1111 1100 252 64 4

VLSM -option


‐> Hierarchical Subnetting

ARP ‐ ARP Cache ‐Package

Encapsulation of ARP packet

Hardware Type Protocol Type

HardwareLength

Protocol Length

Operation

Sender Hardware address

Sender Protocol address

Target Hardware address

Target Protocol address

ARP – Packet Format

Hardware Type Protocol Type

HardwareLength

Protocol Length Operation

Sender Hardware address

Sender Protocol address

Target Hardware address

Target Protocol address

Proxy ARP

ARP Package

ARP Package

• Cache Table

• Queues

• Output Module

• Input Module

• Cache Control Module

ARP Cache Table

STATE H/WType

ProtcolType

H/WLength

ProtcolLength

I/FNum

QNum

Attempt TO H/WAddr

ProtclAddr

Res

Pen

Free

ICMP

Internet ControlMessage Protocol

Why ICMP

What it Does

IP Deficiencies

Lack of Error Control Error Reporting

Lack of Assistance Mechanisms

Query Messages

ICMP

ICMP

TYPES OF MESSAGESMESSAGE FORMAT

ERROR REPORTING MSGQUERY MSG

ICMP PACKAGE

ICMP Encapsulation

ICMP Encapsulation

ARP Reply / Request

ICMP

TYPES OF MESSAGESMESSAGE FORMAT

ERROR REPORTING MSGQUERY MSG

ICMP PACKAGE

ICMP

TYPES OF MESSAGES

ICMP MESSAGE TYPES

ICMP

MESSAGE FORMATERROR REPORTING MSG

QUERY MSG

General format of ICMP messagesCategory Type Message

ErrorReportingMessages

3 Destination Unreachable

4 Source Quench

11 Time Exceed

12 Parameter Problem

5 Redirection

QueryMessages

8 / 0 Echo Req / Rep

13 / 14 Timestamp Req / Rep

ICMP

MESSAGE FORMATERROR REPORTING MSG

QUERY MSG

Error Reporting Messages

ICMP always reports error messages to the original source

• 1. No ICMP error message for a datagram carrying an ICMP error message.

• 2. No ICMP error message for a fragmented datagram that is not the first fragment.

• 3. No ICMP error message for a datagram having a multicast address.

• 4. No ICMP error message for a datagram with a special address such as 127.0.0.0 or 0.0.0.0.

Error‐reporting message Types

Destination Unreachable

CODE 0 : Network Unreachable

CODE 1 : Host unreachable

CODE 2 : Protocol Unreachable

CODE 3 : Port Unreachable

CODE 4 : Fragmentation is required, but DF (do not Frag) is enabled

CODE 5 : Source routing enabled, but couldn’t accomplish

CODE 6 : Dest N/W is unknown

CODE 7 : Dest Host is unknown

CODE 8 : Source Host Isolated

CODE 9 : Dest N/W is administratively Prohibited

CODE 10 : Dest Host is administratively Prohibited

CODE 11 : Network Unreachable for a specified type of service

CODE 12 : Host Unreachable for a specified type of service

CODE 13 : Communication administratively prohibited

(administrative filtering prevents packet from being forwarded)

CODE 14 : Host precedence violation (permission denied for the combination of host or network and port)

CODE 15 : Precedence cutoff in effect

(precedence of datagram is below the level set by the network administrators)

Source Quench

Source Quench

• A source‐quench message informs the source that a datagram has been discarded due to congestion in a router or the destination host.

• The source must slow down the sending of datagrams until the congestion is relieved.

• One source‐quench message is sent for each datagram that is discarded due to congestion.

Time Exceeded

Time Exceeded

• Whenever a router decrements a datagramwith a time‐to‐live value to zero, it discardsthe datagram and sends a time‐exceededmessage to the original source.

• When the final destination does not receive allof the fragments in a set time, it discards thereceived fragments and sends a time‐exceeded message to the original source.

Parameter‐problem message

• Code 0 : Error on Header (Value of pointer points to the byte with problem)

• Code 1 : Options missing

Redirection Message

Redirection Concept

Query message Types

Echo Request Reply Message

Echo Request Reply

• An echo‐request message can be sent by a host or router.An echo‐reply message is sent by the host or routerwhich receives an echo‐request message.

• Echo‐request and echo‐reply messages can be used bynetwork managers to check the operation of the IPprotocol.

• Echo‐request and echo‐reply messages can test thereachability of a host. This is usually done by invoking theping command.

Timestamp Request Reply Message

Timestamp Request Reply Message

• Timestamp‐request and timestamp‐reply messages can be used to calculate the round‐trip time between a source and a destination machine even if their clocks are not synchronized.

• The timestamp‐request and timestamp‐reply messages can be used to synchronize two clocks in two machines if the exact one‐way time duration is known.

Checksum

In ICMP the checksum is calculated over the entire message (header and data).

Lets have an example of checksum calculation for a simple echo‐request message. We randomly chose the identifier to be 1 and thesequence number to be 9. The message is divided into 16‐bit (2‐byte) words. The words are added together and the sum iscomplemented. Now the sender can put this value in the checksumfield.

DEBUGGING TOOLS

PingTraceroute

PING

The ping program to test the server fhda.edu. The result is shown below

$ ping fhda.eduPING fhda.edu (153.18.8.1) 56 (84) bytes of data.64 bytes from tiptoe.fhda.edu (153.18.8.1): icmp_seq=0 ttl=62 time=1.91 ms64 bytes from tiptoe.fhda.edu (153.18.8.1): icmp_seq=1 ttl=62 time=2.04 ms64 bytes from tiptoe.fhda.edu (153.18.8.1): icmp_seq=2 ttl=62 time=1.90 ms64 bytes from tiptoe.fhda.edu (153.18.8.1): icmp_seq=3 ttl=62 time=1.97 ms64 bytes from tiptoe.fhda.edu (153.18.8.1): icmp_seq=4 ttl=62 time=1.93 ms

PING

64 bytes from tiptoe.fhda.edu (153.18.8.1): icmp_seq=5 ttl=62 time=2.00 ms64 bytes from tiptoe.fhda.edu (153.18.8.1): icmp_seq=6 ttl=62 time=1.94 ms64 bytes from tiptoe.fhda.edu (153.18.8.1): icmp_seq=7 ttl=62 time=1.94 ms64 bytes from tiptoe.fhda.edu (153.18.8.1): icmp_seq=8 ttl=62 time=1.97 ms64 bytes from tiptoe.fhda.edu (153.18.8.1): icmp_seq=9 ttl=62 time=1.89 ms64 bytes from tiptoe.fhda.edu (153.18.8.1): icmp_seq=10 ttl=62 time=1.98 ms

--- fhda.edu ping statistics ---11 packets transmitted, 11 received, 0% packet loss, time 10103ms

rtt min/avg/max = 1.899/1.955/2.041 ms

Traceroute

We use the traceroute program to find the route from the computer voyager.deanza.edu to the server fhda.edu :

$ traceroute fhda.edutraceroute to fhda.edu (153.18.8.1), 30 hops max, 38 byte packets1 Dcore.fhda.edu (153.18.31.254) 0.995 ms 0.899 ms 0.878 ms2 Dbackup.fhda.edu (153.18.251.4) 1.039 ms 1.064 ms 1.083 ms3 tiptoe.fhda.edu (153.18.8.1) 1.797 ms 1.642 ms 1.757 ms

ICMP PACKAGE

SLIP & POINT TO POINT PROTOCOL

Serial Line IP Protocol

SLIP - SLIP is a standard protocol for point-to-point serial connections, using TCP/IP. SLIP was a predecessor of PPP.

PROBLEM WITH SLIP PROTOCOL • No Error detection. • It supports only IP.• It is not possible to dynamically assign the address during the set up.• Slip does not provide any Authentication. • It is not approved internet standard.

POINT TO POINT PROTOCOL

PPP provides router‐to‐router and host‐to‐networkconnections over synchronous and asynchronouscircuits.

SERVICES PROVIDED BY PPP:‐• The PPP protocol can operate over a full duplex point to point

transmission link as well as over asynchronous links.• The PPP was an improvement over the SLIP.

PPP ‐ TRANSITIONSTATES

1.DEAD:‐It means that the link is not being used.

2.ESTBLISHING:‐When one of the end machine starts the communication, the connection goes into the establishing state.3.AUTHENATICATING:‐The user sends the authenticate request packet & includes the user name & password.

4.NETWORKING:‐The exchange of user control and data packets can started.

5.TERMINATING:‐The users sends the terminate the link. With the reception of the terminate.

PPP ‐ STACK

PPP is a data link protocol. But it uses stack of other protocols in order to establish the link, to authenticatethe users and to carry the network layer data.

1.Link Control Protocol (LCP).2.Authenticating Protocols .3.Network Control Protocols (NCP).

PPP Stack

PPP ‐ STACK

FLAG:‐The PPP frame always begins & Ends with the Boundary – 01111110

ADDRESS:‐Since PPP is used for a point to point connection , it uses the broadcast address used in most LAN to avoid a data link address in the protocol.

CONTROL:‐This field uses the value 11000000 to show that the frame does not contain any sequence numbers and Its Independent

PROTOCOL:‐It defines what type of data is being carried in the data field

DATA FIELD:‐It carries the user data or other information.

FCS:‐The Frame Check Sequence is simply a2 or 4 byte CRC used for error detection

subnetting,supernetting, vlsm & cidr - srm university 1(3).pdf · • there are several...

Documents