IP Addressing and Routing 1 Basic IP Addressing Each host connected to the Internet is identified by a unique IP address. An IP address is a 32-bit quantity. Expressed as a dotted-decimal notation W.X.Y.Z. Consists of two logical parts: A network number A host number This partition defines the IP address classes. 2 1
IP Address Classes There are five defined IP address classes. Class A Class B Class C Class D Class E UNICAST UNICAST UNICAST MULTICAST RESERVED There are some special-purpose IP addresses also. 3 Class Address Range Highorder bits Network bits Host bits A 0.0.0.0 127.255.255.255 0 7 24 B 128.0.0.0 191.255.255.255 10 14 16 C 192.0.0.0 223.255.255.255 110 21 8 D 224.0.0.0 239.255.255.255 1110 E 240.0.0.0 255.255.255.255 1111 4 2
Special-Purpose IP Addresses Address Range 0.0.0.0 10.0.0.0 10.255.255.255 127.0.0.0 127.255.255.255 172.16.0.0 172.31.255.255 192.168.0.0 192.168.255.255 255.255.255.255 Purpose Unknown network, commonly represents default Reserved for private use Reserved for loopback / local address Reserved for private use Reserved for private use Limited broadcast 5 The class-based addressing is also known as the classful model. Different network classes lend themselves to different network configurations. Different network-to-hosts ratio. 6 3
Some Conventions Within a particular network (Class A, B or C), the first and last addresses serve special functions. The first address represents the network number (for example, 118.0.0.0). The last address represents the directed broadcast address of the network (for example, 118.255.255.255). 7 IP Subnetting 8 4
IP Subnet Basic concept: A subset of a class A, B or C network. IP addresses that do not use subnets consists of a network portion, and a host portion. Represents a static two-level hierarchical addressing model. 9 IP Subnet (contd.) IP subnets introduces a third level of hierarchy. a network portion a subnet portion a host portion Allow more efficient (and structured) utilization of the addresses. Uses network masks. 10 5
Natural Masks Network mask 255.0.0.0 is applied to a class A network 10.0.0.0. In binary, the mask is a series of contiguous 1 s followed by a series of contiguous 0 s. 11111111 00000000 00000000 00000000 Network portion Host portion 11 Natural Masks (contd.) Provide a mechanism to split the IP address 10.0.0.20 into a network portion of 10, and a host portion of 20. Decimal Binary IP address:10.0.0.20 00001010 00000000 00000000 00010100 Mask: 255.0.0.0 11111111 00000000 00000000 00000000 Network Host 12 6
Natural Masks (contd.) Class A, B and C addresses Have fixed division of network and host portions. Can be expressed as masks. Called natural masks. Natural Masks Class A :: 255.0.0.0 Class B :: 255.255.0.0 Class C :: 255.255.255.0 13 Creating Subnets using Masks Masks are very flexible. Using masks, networks can be divided into smaller subnets. How? By extending the network portion of the address into the host portion. Advantage gained: We can create a large number of subnets from one network. Can have less number of hosts per network. 14 7
Example: Subnets Network mask 255.255.0.0 is applied to a class A network 10.0.0.0. This divides the IP address 10.5.0.20 into a network portion of 10, a subnet portion of 5, and a host portion of 20. The 255.255.0.0 mask borrows a portion of the host space, and applies it to network space. 15 Subnets (contd.) What happens? Initially it was a single large Class A network (2 24 2 hosts). We have now split the network into 256 subnets. From 10.0.0.0 to 10.255.0.0. The hosts pet subnet decreases to 65,534. 16 8
Subnets (contd.) Decimal Binary IP address: 10.5.0.20 00001010 00000101 00000000 00010100 Mask: 255.255.0.0 11111111 11111111 00000000 00000000 Network Subnet Host 17 Default Mask and Subnet mask IP Address 144.16.72.57 Default Mask 255.255.0.0 AND Network Address 144.16.0.0 IP Address 144.16.72.57 AND Subnet Mask 255.255.192.0 Network Address 144.16.64.0 192: 1100 0000 72: 0100 1000 18 9
Subnets vrs Multiple Address Classes Subnets Management of subnets is done by local network administrator. Single entry in external router tables. Multiple Address Classes Multiple entries in external router tables. Additional overhead on the backbone (external) routers. 19 Comparison R R SUBNETS R R R MULTIPLE ADDRESS CLASSES R 20 10
Variable Length Subnet Mask (VLSM) 21 Variable Length Subnet Masks (VLSM) Basic concept The same network can be configured with different masks. Can have subnets of different sizes. Allows better utilization of available addresses. 22 11
Example: VLSM Suppose we are assigned a Class C network 192.203.17.0. To be divided into three subnets. Corresponding to three departments. With 110, 45 and 50 hosts respectively. D1 (110) D2 (45) D3 (50) 23 The Example (contd.) Available subnet options The network mask will be the Class C natural mask 255.255.255.0 Subnet masks of the form 255.255.255.X Can be used to divide the network into more subnets. 24 12
The Subnet Options X X (in binary) No. of Subnets No. of Hosts 128 1000 0000 2 128 192 1100 0000 4 64 224 1110 0000 8 32 240 1111 0000 16 16 248 1111 1000 32 8 252 1111 1100 64 4 Cannot satisfy the requirements. 25 The VLSM Option Basic concept: Use the mask 255.255.255.128 to divide the network address into two subnets with 128 hosts each. 192.203.17.0 (.0 to.127) 192.203.17.0 (.128 to.255) 26 13
The VLSM Option (contd.) Next subnet the second.128 subnet using a mask of 255.255.255.192. Creates two subnets, 64 hosts each 192.213.17.128 (.128 to.191) 192.213.17.128 (.192 to.255) 27 The VLSM Option (contd.) 192.203.17.0 Mask: 255.255.255.128 192.203.17.0 (.0 to.127) 192.203.17.0 (.128 to.255) 192.213.17.128 (.128 to.191) Mask: 255.255.255.192 192.213.17.128 (.192 to.255) 28 14
Interface 1 :: 128 hosts Network number: 192.203.17.0 Network mask: 255.255.255.128 Address: 192.203.17.0 --.127 Interface 2 :: 64 hosts Network number: 192.203.17.128 Network mask: 255.255.255.192 Address: 192.203.17.128 --.191 Interface 3 :: 64 hosts Network number: 192.203.17.192 Network mask: 255.255.255.192 Address: 192.203.17.192 --.255 29 128 Hosts E2 64 Hosts E3 ROUTER E4 64 Hosts Interface E3 :: 64 hosts Network number: 192.203.17.128 Network mask: 255.255.255.192 Address range: 192.203.17.128.191 Interface E2 :: 128 hosts Network number: 192.203.17.0 Network mask: 255.255.255.128 Address range: 192.203.17.0.127 Interface E4 :: 64 hosts Network number: 192.203.17.192 Network mask: 255.255.255.192 Address range: 192.203.17.192.255 30 15
VLSM :: Current Status All routing protocols do not support VLSM. Routing Information Protocol version 1 (RIP-1) do not carry network masks in routing updates. RIP-1 cannot implement VLSM. The following protocols support VLSM: Open Shortest Path First (OSPF) RIP-2 Enhanced IGRP (EIGRP) 31 Classless Internet Domain Routing (Supernetting) 32 16
Classless Inter-Domain Routing (CIDR) The size of the global routing tables have grown very fast in recent years. Caused routers to become saturated. Limits to processing power and available memory. Size of the tables have doubled every 10 months or so, between 1991 and 1995. 33 Without any remedial measure, the routing tables would have grown to about 80,000 routes in 1995. But early 2000 data shows that the size was around 76,000. Why this reduction? Planned IP address allocation. CIDR. 34 17
Growth of Internet Routing Tables 80000 70000 60000 50000 40000 30000 20000 10000 0 '88 '94 '96 '98 '00 Routing Table Size Year 35 CIDR: Introduction CIDR is a new concept to manage IP networks. Classless Inter Domain Routing. No concept of class A, B, C networks. Reduces sizes of routing tables. 36 18
CIDR: Basic Idea An IP address is represented by a prefix, which is the IP address of the network. It is followed by a slash, followed by a number M. M: number of leftmost contiguous bits to be used for the network mask. Example: 144.16.192.57 / 18 37 CIDR: An Important Rule The number of addresses in each block must be a power of 2. The beginning address in each block must be divisible by the number of addresses in the block. A block that contains 16 addresses cannot have beginning address as 144.16.223.36. But the address 144.16.192.64 is possible. 38 19
Example: CIDR An organization is allotted a block with beginning address: 144.16.192.24 / 29 What is the range of the block? Start addr: 10010000 00011000 11000000 00011000 End addr: 10010000 00011000 11000000 00011111 There are 8 addresses in the block. 39 Example Suppose Company A needs IP addresses for 1000 machines Assign 4 contiguous Class C address blocks 192.60.128.0 192.60.129.0 192.60.130.0 192.60.131.0 (last 8 bits 0) 40 20
Supernet: Address : 192.60.128.0 Netmask: 255.255.252.0 (last 10 bits 0) Also written as: 192.60.128.0/22 22 denotes size of network portion. Also called prefix. Routing done by prefix 41 Advantages Routing table at higher levels will have only one entry for the 4 networks. In classful addressing (that did not recognize masks), would have required 4 entries for the 4 networks. Possible only due to contiguous allocation. Higher level routers can just send it to lower level routers (in this case company A s router) using one entry only. Lower level router will distinguish. 42 21
Routing table at all higher level routers: 192.60.128.0/22 - send to host X (next hop on way to Company A s router RA) Routing table at RA: 192.60.128.0/24 send to router of first net 192.60.129.0/24 send to router of second net 192.60.130.0/24 send to router of third net 192.60.131.0/24 send to router of fourth net RA 43 Routers always do longest prefix match. If two entries match, longest match is taken. Example: two entries in table: one for 192.65.0.0/16 and one for 192.65.128.0/24. If address is 192.65.128.4, second entry will be used even though it matches both. 44 22
Recent Trend Move on to CIDR addressing. Existing classful networks can also be represented using this notation. Class A: W.X.Y.Z / 8 Class B: W.X.Y.Z / 16 Class C: W.X.Y.Z / 24 Recent routers support CIDR. 45 23