Internetworking With TCP/IP

Internetworking With TCP/IP Application Layer Telnet Gopher NFS FTP X Win TFTP SMTP SNMP REXEC DNS RPC Transport Layer TCP UDP Network Layer ICMP IP IGMP ARP RARP Link Interface Ethernet, IEEE 802.3, Token Ring, X.25, SNA, FDDI,. Parviz Kermani IPv4 Addressing in

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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 3

Internet in a Nutshell Application Layer Telnet Gopher NFS FTP X Win TFTP SMTP SNMP REXEC DNS RPC Transport Layer TCP UDP Network Layer ICMP IP IGMP ARP RARP Link Interface Ethernet, IEEE 802.3, Token Ring, X.25, SNA, FDDI,. 4

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) 5

Layer 2 Addressing Uses MAC address Assigned to end devices 6

Layer 3 Addressing Each Network Architecture has its own Layer 3 address format. OSI uses NSAP. TCP/IP uses IP 7

Host-to-Host Packet Delivery (1 of 10) 8

(Classical) (Layer 3) IP address is 32 bit An An IP address is broken in two parts Network address Host address Network host The division between network and host is determined by the size of network and determined by the class of the address 18

IP Addresses classful addressing class A B C 0 network host 10 network host 110 network host 1.0.0.0 to 127.255.255.255 128.0.0.0 to 191.255.255.255 192.0.0.0 to 223.255.255.255 D 1110 multicast address 32 bits 224.0.0.0 to 239.255.255.255 19

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 20

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 21

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 Note: The third column is the Number of Networks (and not IP Addresses) 22

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! 23

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. 24

Manageability: Subnetworks The Smaller networks are easier to manage. Overall traffic is reduced. You can more easily apply network security policies. 1-25

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 (2 11 =2048) In practice the 11 bit rightmost addressing could be further divided (subnetting, more on this later) network part host part 11001000 00010111 00010000 00000000 152.23.16.0/21 26

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 Ex (classful address): Addr = 9.2.225.65/8 = 00001001.00000010.11100001.01000001 Mask = 11111111.00000000.00000000.00000000 = 255. 0. 0. 0 27

Mask examples (classful addresses) Ex-1: Addr = 9. 2. 225. 65/8 = 00001001.00000010.11100001.01000001 Mask = 11111111.00000000.00000000.00000000 = 255. 0. 0. 0 N-Adr= 10001001.00000000.00000000.00000000 9.0.0.0 Ex-2 Addr = 156. 204. 135. 160/19 = 10011100.11001100.10000111.10100000 Mask = 11111111.11111111.11100000.00000000 = 255. 255. 224. 0 N-Adr= 10011100.11001100.10000000.00000000 156. 204. 128. 0 28

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 29

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 30

Possible Subnets and Hosts for a Class C Network 31

Possible Subnets and Hosts for a Class B Network 32

Possible Subnets and Hosts for a Class A Network 33

End System Subnet Mask Operation 34

Topology Example A network topology using one IP network with six subnets 35

How Routers Use Subnet Masks 36

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? 37

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 38

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 39

Subnetting: A useful reference chart 40

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 41

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 3 rd byte) Mask: 1. 1.11111100.00000000; 255.255.252.0 Subnet number: 148.214.16.0 (0001000.00000000) Next/previous subnets: Next: 16+4=20 (192.214.20.0) Previous: 16-4=12 (192.214.12.0) Range of addresses: 192.214.16.1 to 192.214.19.255) Broadcast address: 199.214.19.255 First IP address: 199.214.16.1 Last IP address: 199.214.19.254 42

Example: 9.214.17.132/12 (Class A) IP@: Borrowed bits: ; Net bits: ; Host bits: Block size: (in the byte) Mask: Subnet number: Next/previous subnets: Next: Previous: Range of addresses: Broadcast address: First IP address: Last IP address: 43

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 Step 2: Compare the range of addresses in each subnet and look for any overlap 44

The Dread of Overlapping Subnets Is there any flaw in the following network? 45

Problem Network 2 172.16.4.2/23 1 172.16.2.1/23 3 172.16.5.2/24 46

The Dread of Overlapping Subnets 172.16.2.1/23 Mask: 255.255.254.0 Subnet number: 172.16.2.0 Broadcast @: 172.16.3.255 172.16.4.1/23 Mask: 255.255.254.0 Subnet number: 172.16.4.0 Broadcast @: 172.16.5.255 172.16.5.1/24 Mask: 255.255.255.0 Subnet number: 172.16.5.0 Broadcast @: 172.16.5.255 Overlap! 47