Internetworking With TCP/IP
IPv4 Addressing in
Ethernet, IEEE 802.3, Token Ring, X.25, SNA, FDDI, …. TCP UDP Telnet Gopher NFS FTP X Win TFTP SMTP SNMP REXEC DNS RPC Application Layer Transport Layer Network Layer Link Interface
ICMP IP IGMP ARP RARP
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Acknowledgement
Part of the following pages were taken from
materials provided by other authors and
companies
Cisco
Lecture slides of “Computer Networking: A Top Down Approach” by Jim Kurose and Keith Ross “CCENT/CCNA ICND1 & 2- Official Exam
Certification Guide”, Wendell Odom, Cisco Press
Internet in a Nutshell
Ethernet, IEEE 802.3, Token Ring, X.25, SNA, FDDI, ….
TCP UDP Telnet Gopher NFS FTP X Win TFTP SMTP SNMP REXEC DNS RPC Application Layer Transport Layer Network Layer Link Interface
ICMP IP IGMP ARP RARP
Addresses & Names
Hardware (Layer 2)
Lowest level
Ethernet (MAC), Serial point-to-point, ..
Network (Layer 3)
IP
IPX, SNA, others
Application (layer 5?)
Names (URL), alias, ..
All are important and needed
Ultimately, all deliveries move over the physical layer
Note: Port address not under discussion (Transport)
Layer 2 Addressing
Uses MAC address
Assigned to end devices
Layer 3 Addressing
Each Network Architecture has its own Layer 3 address format.
OSI uses NSAP.
TCP/IP uses IP
Host-to-Host Packet Delivery (1 of 10)
Host-to-Host Packet Delivery (2 of 10)
Host-to-Host Packet Delivery (3 of 10)
Host-to-Host Packet Delivery (4 of 10)
Host-to-Host Packet Delivery (5 of 10)
Host-to-Host Packet Delivery (6 of 10)
Host-to-Host Packet Delivery (7 of 10)
Host-to-Host Packet Delivery (8 of 10)
Host-to-Host Packet Delivery (9 of 10)
Host-to-Host Packet Delivery (10 of 10)
(Classical) IP Addressing (Layer 3)
IP address is 32 bit
An An IP address is broken in two parts
Network address Host address
The division between network and host is
determined by the size of network and
determined by the “class” of the address
Network host
IP Addresses
IP Classful Addresses:
Class A addresses begin with 0xxx, or 1 to 126 Class B addresses begin with 10xx, or 128 to 191 Class C addresses begin with 110x, or 192 to 223 Class D addresses begin with 1110, or 224 to 239
Multicast
Class E addresses begin with 1111, or 240 to 254 Experimental
Classful Addressing
Number of
elements
in each class
Class Number of
classes Number of local addresses
A 0xxx 128 16,777,216
B 10xx 16,384 65,534
C 110x 2,097,152 254
Private IP Addresses Space
Private IP Networks Class of Network Number of Networks 10.0.0.0 to 10.0.0.0 A 1 172.16.0.0 to 172.31.0.0 B 16 192.168.0.0 to 192.168.255.0 C 256 IP Addressing 22
Note: The third column is the Number of
Problems with Classful Addressing
Inefficient use of address space, address
space exhaustion
e.g., class B net allocated enough addresses for 65K hosts, even if only 2K hosts in that network
Network manageability (discussed below)
No longer formally part of IP addressing
architecture
Note:
A classful address identifies the “Network” and “Host” field
No need for “Network Mask”!
Manageability: Flat Topology
Problems
All devices share the same bandwidth.
All devices share the same broadcast domain. It is difficult to apply a security policy.
Manageability: Subnetworks
The Smaller networks are easier to manage. Overall traffic is
reduced.
You can more easily apply network security policies.
IP addressing: CIDR
CIDR: Classless InterDomain Routing Adopted by IETF in 1993
Network (subnet) portion of address of arbitrary length
address format: a.b.c.d/x, where x is # bits in network (subnet) portion of address
To support 2000 hosts, a block of 2048 addresses of the form a.b.c.d/21 assigned
11 bits needed to store 2048 (211=2048)
In practice the 11 bit rightmost addressing could be further divided (subnetting, more on this later)
Network Mask
With CIDR, address no longer specifies the network portion
Mask is used to extract network portion from an IP Address
A string of 32 bits
Bits corresponding to network (and subnet) part set to ‘1’ Bits corresponding to host part set to ‘0’
Two-Level and Three-Level Addresses
Inefficiency of two-level addresses
A third level of addressing, consisting of
subnets, was developed
Subnet address:
The original classful network
portion plus a subnet field
Also known as extended network field
Subnet and host field created from the original classful host portion
Subnet Mask helps identify the host/network
part of an address
What a Subnet Mask Does
Tells the router the number of bits to look at when routing
Defines the number of bits that are significant Used as a measuring tool, not to hide anything
Possible Subnets and Hosts for a Class C
Network
Possible Subnets and Hosts for a Class B
Network
Possible Subnets and Hosts for a Class A
Network
End System Subnet Mask Operation
Topology Example
A network topology using one IP network with six subnets
How Routers Use Subnet Masks
Working with subnets and masks:
Analysis
Analysis of a given IP address/mask
Binary/decimal mask
Subnet number (network prefix) Next/previous subnet
Range of addresses Broadcast address The first IP address The last IP address
Important: are networks specified by 2 addresses overlapping?
Working with subnets and masks: Design
Choosing a subnet mask to meet design
requirements
Finding the only possible mask Finding multiple possible masks
Choosing the mask that maximizes the number of subnets or hosts
Subnet addresses
Reserved addresses:
The smallest address (all “0”s) signifies the subnet number
128.12.17.144/28: x.y.z.10010000
10.12.16.128/26: x.y.z.10000000
The last address (all “1”s) signifies the broadcast address
128.12.15.159/28: x.y.z.10011111
10.12.16.191/26: x.y.z.10111111
Subnetting: A useful reference chart
Example: 199.214.17.132/28 (Class C)
IP@:x.y.z.10000100
Borrowed bits: 4; Net bits: 28; Host bits: 4
Block size 16
Mask(last byte only): 11110000; 240
Subnet number: 199.214.17.128 (10000000) Next/previous subnets:
Next: 128 + 16= 144 (10010000)
Previous: 128 – 16 = 112 (01110000)
Range of addresses: x.y.z.129 to x.y.z.143 Broadcast address: 199.214.17.143
First IP address: 199.214.17.129 Last IP address: 199.214.17.142
Example: 148.214.17.132/22 (Class B)
IP@:x.y.00010001.10000100
Borrowed bits: 6; Net bits: 22; Host bits: 10
Block size: 4 (in the 3rd byte)
Example: 9.214.17.132/12 (Class A)
IP@:
Borrowed bits: __; Net bits: __; Host bits: __
Block size: __ (in the __ byte)
The Dread of Overlapping Subnets
In designing networks, care should be taken
to prevent overlapping subnets
Step 1: calculate the subnet number and
subnet broadcast address of each subnet.
Determines range of addresses within each subnet
