高级计算机网络--Lecture 5-2 v2.pdf

Advanced Computer NetworkLecture 4:The Network Layer in TCP/IPYunmingYeDepartment of Computer ScienceShenzhen Graduate SchoolHarbin Institute of TechnologyAgenda Introduction to IP Protocol IP Addressing Routing Protocols on Internet ICMP IPV6 Address Resolution Protocols A Quiz2010年5月24日星期一2Introduction to IP Protocol3TCP/IP Protocol StackTELNETFTPSMTPDNSProtocols/32 bit source IP address32 bit destination IP addressOptions(if any)data(variable length,typically a TCPor UbP segment)E.g.timestamp,record routetaken,specifylist of routersto visit.2010年5月24日星期一6Header Fields(1)Version Currently 4 IP v6-see later Internet header length In Bytes Including options Type of service Total length Of datagram,in octets2010年5月24日星期一7Header Fields(2)Identification Sequence number Used with addresses and user protocol to identifydatagram uniquely Flags More bit Dont fragment Fragmentation offset Time to live Protocol Next higher layer to receive data field atdestination2010年5月24日星期一8Header Fields(3)Header checksum Reverified and recomputed at each router 16 bit ones complement sum of all 16 bit words inheader Set to zero during calculation Source address Destination address Options2010年5月24日星期一9Data Field Carries user data from next layer up Integer multiple of 8 bits long(octet)Max length of datagram(header plus data)65,535 octets2010年5月24日星期一10Layer 3 Devices Routers Interconnect networksegments“entirenetworks Make logicaldecisions based on IPaddresses Determine best pathfor data on aninternetwork(routingof packets)tThhaet oalnlolyw ws aHyo Hsot sBt tBo creaanc rhe aHcohs tH Ao.s Wt Ait hiso uwti tthh ea ns uapdpdorerts soifn nge stwchoerkmelayer services,Host B can not determine where Host A resides.Cisco Syafems Inc 19992010年5月24日星期一11Path determination Path determination is the process that the routeruses to choose the next hop in the path for thepacket to travel to its destination based on thelink bandwidth,hop,delay 2010年5月24日星期一12IP addresses IP addresses are implemented in software,andrefer to the network on which a device is located.IP addressing scheme,according to theirgeographical location,department,or floor withina building,Because they are implemented in software,IPaddresses are fairly easy to change.2010年5月24日星期一13Router and BridgePH ApplicationTl Presentation5j Session-4|Transport巨 Network T Data LinkAssigned by NetworkAdministratorAssigned by Network InterfaceCard Manufacturer口 Physical2010年5月24日星期一14Router connections Routers connect two or more networks,each of whichmust have a unique network number in order for routingto be successful.The unique network number is incorporated into the IPaddress that is assigned to each device attached to thatnetwork.2010年5月24日星期一15Router InterfaceRouter2010年5月24日星期一16201(Router functionA12Network AcTNetwork C Network DRouter function(cont.l)Strips off the data link header,carried by the frame.(The data link header contains theMAC addresses of the source anddestination.)201CI 1/j j i iz e-，y jRouter function(cont-2)Examines the network layeraddress to determine thedestination network.201CI 1/j j i iz e-，y jDm ifpr fi inctinn(rnnt 2、Consults its routing tables todetermine which of its interfaces itwill use to send the data,in orderfor it to reach its destinationnetwork.201CI j j iRouter function(cont-4)Send the data out interface B1,therouter would encapsulate the datain the appropriate data link frame.201CI 1/j j i iz e-，y jRouter Interface example Interface is a router5s attachment to a network,itmay also be referred to as a port in IP routing,Each interface must have a separate,uniquenetwork address.2010年5月24日星期一22IP Addressing23Network Layer Addresses IP addresses ese 32 bits long.They are represented as four octets indotted decimal format.233.14.17.0 The IP address has two components:The network IDThe host ID2010年5月24日星期一24Layer 3 Addresses Network ID assigned by ARIN(American Registry forInternet Numbers,)identifies the network towhich a device is attached may be identified by one,two,or three of the firstthree octets Host ID assigned by a networkadministrator identifies the specificdevice on that network may be identified by one,two,or three of the lastthree octets2010年5月24日星期一25IP Addresses 32 bit address represented as 8 bit dotted decimals different class addresses reserve different amountsof bits for the network and host portions of theaddressClass ANHHHClass BNNHHClass CNNNH2010年5月24日星期一26Number of Hosts The maximum number of hosts vary for each class.Class A has 16,777,214 available hosts(224-2)Class B has 65,534 available hosts(2作 一2)Cass C has 254 avaHable hosts 之 一2)The first address in each network is reservedfor the network address and the gst addressis reserved f o the broadcast address.2010年5月24日星期一27IP Address Bit Patterns10NETWORK#HOST#-NETWORK#16HOST#2010年5月24日星期一28Classes How do you know what class an IP address is in?0 T 2 7 Class Aaddress工 28191Class Baddress工 92-223 Oass Caddress224-239 Class D一 Multicast240-255 Class E-Research一 J 一lass RNET。