Lec 5(Ip Addressing and Subnets)
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This document provides an overview of IP addressing and subnetting. It discusses how IPv4 addresses are 32-bit identifiers written in dotted decimal notation. It also explains how classless inter-domain routing (CIDR) allows flexible subnet masks and more efficient address block allocation. The document gives examples of subnetting an IP address range into multiple subnets and calculating the network addresses, masks, and host ranges for each subnet.
Lec 5(Ip Addressing and Subnets)
- 1. Computer Networks – CSE331 Lecture 5
- 2. Unique number that represent universally defines connection of a device (a router, computer etc) IPv4 address is 32bit long identifier The address space is 232 or 4,294,967,296 (more that 4 billion) 4 octets each separated by a dot (dotted decimal notation) Each octet is of b bits so 0-255 value 128.11.3.31
- 3. First address is 146.102.29.0 and the last address is 146.102.32.255 Subtract first address from last in base 256 0.0.3.255 Convert this to base 10 & add 1 See more examples from Forouzan book chapter 5 (Review your concepts for number conversion)
- 4. The network prefix identifies a network and the host number identifies a specific host (actually, interface on the network). Two level addressing How do we know how long the network prefix is? The network prefix used to be implicitly defined (class-based addressing, A,B,C,D…) The network prefix now is flexible and is indicated by a prefix/netmask (classless) network prefix host number
- 5. Address is associated with interface 223.1.1.1 223.1.1.2 223.1.1.3 223.1.1.4 223.1.2.9 223.1.2.2 223.1.2.1 223.1.3.2223.1.3.1 223.1.3.27
- 6. When Internet addresses were standardized (early 1980s) 5 Classes Network Prefix
- 7. Wastage – not enough addresses an organization require Routing table issue If 2000 address are required? A & B class are much more 8 class C addresses Flexibility required 1 bit reserved so 27 blocks Hence 128 organizations 24 bits are of host part Hence 224 hosts in each 127.x.x.x is reserved for loopback address For complete list see reading material slide
- 8. Subnetting Problem: Organizations have multiple networks which are independently managed Solution 1: Allocate an address for each network Difficult to manage From the outside of the organization, each network must be addressable i.e have an identifiable address. Solution 2: Add another level of hierarchy to the IP addressing structure University Network Medical School Library Engineering School
- 9. 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 network prefix host number subnet numbernetwork prefix host number extended network prefix
- 11. Will be more in Lab
- 12. CIDR: Classless InterDomain Routing subnet portion of address of arbitrary length address format: a.b.c.d/x, where x is # bits in subnet portion of address Purchase what you need 11001000 00010111 00010000 00000000 subnet part host part 200.23.16.0/23
- 13. Can not judge block by looking at address 230.8.24.56 could belong to many blocks So prefix is required, suffix can be changed
- 14. Given 17.63.110.114/24 Prefix & Suffix length No of addresses? Network mask? First address? Last address? Given 110.23.120.14/20 Prefix & Suffix length No of addresses? Network mask? First address? Last address? => 232-24 = 28 = 256 255.255.255.0 17.63.110.0 17.63.110.255 => 232-20 = 212 = 4096 20 bits are 1 => 255.255.240.0 First 20 bits => 110.23.112.0 First 20 bits fix, last 12 bits 1 => 110.23.127.255 24 and 8 20 and 12
- 15. CIDR Block Prefix # of Host Addresses /27 32 hosts /26 64 hosts /25 128 hosts /24 256 hosts /23 512 hosts /22 1,024 hosts /21 2,048 hosts /20 4,096 hosts /19 8,192 hosts /18 16,384 hosts /17 32,768 hosts /16 65,536 hosts /15 131,072 hosts /14 262,144 hosts /13 524,288 hosts
- 16. 206.0.64.0/18 204.188.0.0/15 209.88.232.0/21Internet Backbone ISP K owns: Company X : 206.0.68.0/22 ISP Y : 209.88.237.0/24 Organization Z1 : 209.88.237.192/26 Organization Z2 : 209.88.237.0/26 Backbone sends everything which matches the prefixes 206.0.64.0/18, 204.188.0.0/15, 209.88.232.0/21 to ISP K. ISP K sends everything which matches the prefix: 206.0.68.0/22 to Company X, 209.88.237.0/24 to ISP Y Backbone routers do not know anything about Company X, ISP Y, or Organizations Z1, Z2. ISP K does not know about Organizations Z1, Z2. ISP Y sends everything which matches the prefix: 209.88.237.192/26 to Organizations Z1 209.88.237.0/26 to Organizations Z2
- 17. Some Address is 152.4.3.9/21 We have to make 4 subnets Find address for each subnet How many bits are now part of subnet address How many host we can attach in a subnet What is the network mask for each subnet What is the first & last address for each subnet
- 18. Forouzan book Chapter 5 Leave NAT Reserved addresses http://www.inetdaemon.com/tutorials/internet/ip/addresses/specia l.shtml http://www.iana.org/assignments/iana-ipv4-special-registry/iana- ipv4-special-registry.xhtml Or See Original RFC http://www.rfc-editor.org/rfc/rfc5735.txt