IP Network Layer Overview Addressing Routing TOC IP Overview Goals and Tasks Routing Switching Issues Basic ideas TOC IP Overview Goals and Tasks Goals of Network Layer Addressing Guide packets from source to destination Use network links efficiently e g prefer shorter and faster routes Agree on addressing scheme to identify nodes IP addresses are location based similar to telephone numbers This structure reduces the information routers must keep Different types of addresses Routing Routers exchange information to learn network topology Routers then calculate good routes to the different destinations Routers store the results of these calculations in routing tables Different routing algorithms TOC IP Overview Goals and Tasks Routing Definition Types Path based on SS S S Finding path from source to destination AA S S D D 1 1 2 2 33 BB S S D D 1 1 2 2 33 CC S S D D 1 1 4 4 5 5 33 Flow Type or Traffic Source Destination Destination Internet 22 11 33 44 TOC IP Overview Routing 55 Voice Voice S S D D 1 1 2 2 33 Data Data S S D D 1 1 4 4 5 5 33 S S D D 1 1 2 2 33 S S D D 1 1 4 4 5 5 33 DD D D S S D D 1 1 2 2 33 S S D D 1 1 2 2 33 Switching Definition Sending the bits along the path Approaches Circuit Telephone Lightwave Packet Virtual Circuit ATM Datagram Ethernet IP Notes A circuit or VC can be a link in an IP network An Ethernet LAN can be a link in an IP network TOC IP Overview Switching Switching cont Datagram v s Virtual Circuit Datagram routing Virtual Circuit Each packet to be forwarded independently Each packet from same flow uses same route More state pick the right granularity QoS sensitive networks use VC s and signaling Find a route that has the resources available for the connection Reserve the resources before sending data packets TOC IP Overview Switching Issues Scalability great in IP Topology Changes good in IP Millions of nodes Routing tables should remain small Updates should be manageable Routers compute new routes as topology changes Changes should not affect most tables Performance poor in IP Link utilization should be well balanced not in practice Updates should be fast not always Ideally some flows would have a guaranteed rate no Network should detect configuration errors or other errors no Network should protect itself against attacks no TOC IP Overview Issues Basic Ideas Addressing Layer 2 Local scheme typically flat not scalable Layer 3 Location based and hierarchical scalable Temporary addresses for mobile nodes Network Address Translation to reuse addresses Routing Route is based on destination only roughly shortest path Network decomposed into domains Interdomain routing Uses a path vector algorithm Intradomain routing Uses a link state or a distance vector algorithm Variations Multicast P2P Ad Hoc Sensors Content Distribution Networks Addressing Examples Class Based Addressing CIDR Classless Interdomain Routing Assigning Addresses DHCP Network Address Translation TOC IP Addressing Examples Flat Addressing Hierarchical Addressing Internetworking Layers 2 and 3 TOC IP Addressing Examples Flat Addressing 2 2 bb 3 3 aa 4 4 aa 5 5 aa 6 6 aa Address 11 b a Ports a a 22 b 1 1 aa 3 3 bb 4 4 bb 5 5 bb 6 6 bb 33 b c 1 1 aa 2 2 bb 4 4 cc 5 5 cc 6 6 cc a 44 b 1 1 aa 2 2 aa 3 3 aa 5 5 cc 6 6 bb c a 55 b a 66 b 1 1 aa 2 2 aa 3 3 aa 4 4 aa 5 5 bb Routing Table One per node Destination Exit Port Addresses are arbitrary not based on topology e g Ethernet N nodes N 1 entries in every routing table not scalable TOC IP Addressing Examples Flat 1 1 aa 2 2 aa 3 3 aa 4 4 aa 6 6 bb Hierachical Addresses 1 2 1 2 aa 1 3 1 3 bb Default Default cc 1 3 1 3 bb Default Default aa 1 2 1 2 b a a 1 1 1 1 b c a 1 3 1 3 b 1 2 1 2 aa Default Default bb 2 2 2 2 cc 2 3 2 3 bb Default Default aa a 2 1 2 1 b 2 3 2 3 bb Default Default aa c a 2 3 b a 2 3 2 2 2 2 bb Default Default aa Addresses are arranged based on topology e g IP Few entries in each routing table scalable TOC IP Addressing Examples Hierarchical 2 2 2 2 b Internetworking Recall the basic internetworking scheme of IP z u 1 4 3 8 data 1 1 local local IP Default Default yy 1 2 1 2 t t Local 1 7 1 7 yy 1 1 local local 4 bb 4 Default Default aa v w 1 4 3 8 data 1 4 1 4 xx 1 7 1 7 yy 2 5 z a 1 4 x 1 7 y 1 2 t 2 4 u d a b x y 1 4 3 8 data TOC IP Addressing Examples Internetworking 3 6 v 3 8 w Layers 2 and 3 Ethernet Switch Ethernet Switch Router p Destination Address B Next Hop C Local address C Layer 2 address y Application Destination Address B Local to port p Local address B Layer 2 address w Transport Network A Link x Phy Link Phy Phy Phy Network C D Link Link y v Phy Phy TOC IP Addressing Examples Layers 2 3 Link Phy Phy Phy Application Transport Network B Link w Phy Class Based Addresses Addresses Scalability Problem TOC IP Addressing Class Addresses Addressing reflects internet hierarchy 32 bits divided into 2 parts Class A Class B Class C 8 0 0 network 0 10 0 110 host 16 network host 24 network TOC IP Addressing Class Addresses host 2 million nets 256 hosts Scalability Problem Example an organization initially needs 100 addresses Allocate it a class C address Organization grows to need 300 addresses Class B address is allocated 64K hosts That s overkill a huge waste Only about 8200 class B addresses Artificial Address crises TOC IP Addressing Class Scalability Classless Internet Domain Routing CIDR CIDR allows networks to be assigned on arbitrary bit boundaries Address ranges can be assigned in chunks of 2k k 1 32 Idea use aggregation provide routing for a large number of customers by advertising one common prefix This is possible because nature of addressing is hierarchical Summarization reduces the size of routing tables but maintains connectivity Aggregation Scalability and survivability of the Internet TOC IP Addressing CIDR CIDR cont Suppose fifty computers in a network are assigned IP addresses 128 23 9 0 128 23 9 49 They share the prefix 128 23 9 Is this the longest prefix Range is 01111111 00001111 00001001 00000000 to 01111111 00001111 00001001 00110001 How to write 01111111 00001111 00001001 00X Convention 128 23 9 0 …
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