Chapter 9 The Internet 9.1 Introduction 9.2 IP Datagrams 9.3 Fragmentation and reassembly 9.4 IP addresses 9.5 ARP and RARP 9.6 Routing Algorithms 9.7 ICMP 9.8 QoS support 9.9 PPP link layer protocol 9.10 IPv6 9.11 IPv6/IPv4 Interoperability
9.1 Introduction Internet Internet protocol Internet address or IP address
Internet Technology Internet Packets are like Postcards To/From addresses Finite but variable content Delivery failures Duplication (not normally a postal service) Disorderly arrival Variable delays Alternate routes/carriers
IP Addresses Assigned by the NIC (Network Information Center) 호스트의인터넷주소에대응하는숫자주소 4 개의숫자와마침표로구성 203.252.192.1 구성 네트웍주소 호스트주소 세계적으로고유함 NIC (NIDA: National Internet Development Agency) 에등록 국제적협조필요
IP Address Format IP 주소유형 Class A Class B Class C Class D 7 bits 24 bits 0 netid hostid [1-127] 1 0 netid netid hostid [128-191] 14 bits 16 bits [0-255] 1 1 0 netid netid netid hostid [192-233] [0-255] 21 bits 8 bits 28 bits [0-255] 1 1 1 0 Multicast address
Domain of IP 인터넷호스트의지정방식 userid@host-name.domain-name 계층적으로구성 Top-level domain 국가별 기관별 Sub Domain eg) sookmyung.ac.kr
Internet networking components and protocols
IP Adjunct protocols
9.2 IP Datagrams Basic unit of Internet transfer Analogous to physical network packet Composed of Header that contains source and destination Internet addresses, datagram type field, etc. Data area that contains data being carried Encapsulation IP datagram travels in physical network packet or frame Complete datagram is treated as data by the hardware TCP/IP defines standards for encapsulation on most network hardware
IP datagram Format
9.3 Fragmentation and reassembly
Network MTU Each network h/w technology imposes a fixed limit on the maximum size of a packet Size limit called Maximum Transmission Unit (MTU) Encapsulated datagram must be less than network MTU
Datagram Fragmentation Needed when datagram larger than network MTU over which it must travel Performed by routers Divides datagram into several, smaller datagrams called fragments Each fragment routed as independent datagram Final destination reassembles fragments
Datagram Fragmentation Details Each fragment is a datagram Router replicates initial datagram header for all fragments Offset field in header gives offset in original datagram for data in this fragment Fragment bit in header indicates this is a fragment Additional bit set in header to indicate last fragment
Example of Fragmentation Original datagram header Data1 400bytes Data2 400bytes Data3 400bytes header1 Data1 Fragment #1 (offset of 0) header2 Data2 Fragment #2 (offset of 400) header3 Data3 Fragment #3(offset of 800)
9.4 IP address
Subnet addressing
IP Address(1) 32bits 구성됨. Class A, Class B, Class C 가있음 인터넷을위한 IP Address 는공인기관으로부터할당받아야하며, Network Number 만을할당받음 Host Number 는네트웍관리자가원하는대로활용가능 Network (N) Host (H) 164 124 116 5 8bits 8bits 8bits 8bits Class A Class B Class C N H H H N N H H N N N H
IP Address(2) Class A Class B Class C 1 7 24 0 N H 1 1 14 16 1 0 N H 1 11 21 8 1 1 0 N H Network # 갯수 1 개의 Network # 내의이용가능한 Host Number 수 첫 1Byte의십진수범위 Class A 1 ~ 126 (126 개 ) 16777214 개 (256^3-2) 1 ~ 126 Class B 128.1 ~ 191.254 (32766 개 ) 65534 개 (256^2-2) 128 ~ 191 Class C 192.0.1 ~ 223.255.254.0 (2097150 개 ) 254 개 (256^1-2) 192 ~ 223
Network 별 Network Number 할당 LAN, WAN별로동일한 Network Number를이용함 164.124.1.2 164.124.100.3 164.124.180.5 WAN (serial link) 에서는 2개의 Host Number만이용하며 neta A 164.124.0.1 203.252.2.1 나머지는모두사용하지못함 netb 203.252.2.2 시스템의 Interface 별 로 Host Number 를이 netc B netd 용함 130.1.50.0 203.252.3.2 203.252.3.3 130.1.100.10 203.252.3.1
Sub Network Number 할당 4개의네트웍을위해 1 개의 Class B Network Number 164.124 만을이용함 네트웍별로다른 Network Number를가져야된다는것과상충함 Subnetmask로해결 시스템수가적을경우는 Class C의 Sub Network Number 를할당하는것이바람직 164.124.1.2 neta netc 164.124.3.2 164.124.1.3 164.124.1.4 164.124.1.1 A 164.124.2.1 netb 164.124.2.2 B netd 164.124.4.2 164.124.4.3 164.124.3.1 164.124.4.1
Subnetmask Class A IP Addr 본래 netmask masking N H H H 60 1 2 3 255 0 0 0 60 0 0 0 Class A IP Addr new netmask masking N H H H 60 1 2 3 255 255 0 0 60 1 0 0 Class B IP Addr 본래 netmask masking N N H H 164 124 116 5 255 255 0 0 164 124 0 0 Class B IP Addr new netmask masking N N H H 164 124 116 5 255 255 255 0 164 124 116 0 Class C IP Addr 본래 netmask masking N N N H 203 252 3 1 255 255 255 0 203 252 3 0 Class C IP Addr new netmask masking N N N H 203 252 3 66 255 255 255 192 203 252 3 64
Basic Network Configuration 130.120.0.2/16 130.130.1.1/24 130.130.2.2/24 130.130.1.2/24 e0 B s0 s1 s0 s1 C 130.140.0.1/16 130.120.0.1/16 130.130.2.1/24 e0 e0 130.140.0.2/16 e0 A e1 130.100.1.1/24 D e1 130.150.0.2/16 130.150.0.1/16 e1 E /16 은 subnetmask 가 1bit~16bit 까지 1 임을의미하므로 255.255.0.0 을의미 /24 은 subnetmask 가 1bit~24bit 까지 1 임을의미하므로 255.255.255.0 을의미 e0 는 interface ethernet 0 를의미, s0 는 interface serial 0 를의미
IP Address 설정 (in Router) global config mode에서특정 interface를지정한후 IP Address 및 netmask 입력 description은생략되어도되지만 ip-address는꼭지정되어야함 shutdown이선언되어있는경우 no shutdown을입력해야함 Router(config)# interface interface-type [slot/]port Router(config-if)# description description-for-this-interface Router(config-if)# ip address ip-address netmask Router(config-if)# no shutdown Router(config-if)# Ctrl-Z Router#
Data Link Protocol 설정 LAN용 Interface에는별도로 data link protocol을설정하지않아도되지만 WAN용 Interface에는 IP Address와함께data link protocol 을설정해야함 대응하는라우터의 Interface에서도동일한 datalink protocol을지정해야함 HDLC, PPP, X25, Frame-Relay등을지정할수있음 CISCO 라우터에서는 default로 HDLC를이용함 PPP는표준이므로 CISCO 제품이아닌라우터와연결할때에는 PPP를이용할것을권장
Address 설정확인 Application telnet Transport telnet ping trace Application Transport telnet Internet ICMP trace Network Interface Hardware ICMP Internet trace Network Interface Hardware
Internet Address Resolution Protocol (ARP) Internet standard for dynamic address binding Allows machine A to find machine B s physical address knowing only B s Internet address Uses hardware broadcast ARP only used to map addresses within a single physical network, never across multiple networks ARP details ARP table is merely a cache Entries should time out and be invalidated Machine can broadcast new binding when it boots
ARP request and reply messages (2) Machine A broadcasts ARP request with B s IP address All machines on local net receive broadcast Machine B replies with its physical address Machine A adds B s address information to its table Machine A delivers packet directly to B
ARP request and reply messages (2) A broadcasts request for B (across local net only) A X B Y B replies to request A X B Y
Algorithm for Processing ARP Requests Extract sender s pair, (Ia, Ha) and update local ARP table If this is a request and the target is me Fill in target h/w address Exchange sender and target entries Set operation to reply Send reply back to requester
9.6 Routing algorithm Routing in an Internet Host delivers datagrams to directly connected machines Host sends datagrams that can not be delivered directly to router Routers forward datagrams to other routers Final router delivers datagram directly Routing protocol 데이타를 encapsulation해서전달하기위한 protocol로 IP, IPX, Appletalk등이이에해당된다. routing protocol이라는것은 IP packet, IPX packet, Appletalk packet등을전달할때경로정보를교환, 관리하기위한 protocol이다. IP는 routing protocol로 RIP, IGRP, OSPF, BGP등을, IPX는 Novell RIP, NLSP등을, Appletalk은 RTMP를이용한다.
Example internetwork topology Line ID, cost
Network Layer & Routing Protocol Network Layer 는시작 (source) 에서부터목적지 (destination) 까지 Packet 을전달 Routing Protocol 은라우터간에경로정보를주고받는 Protocol S S app pre ses trans net data phy r1 net data phy 1 2 r2 r3 net data phy 4 5 3 r4 r5 net data phy 6 7 r6 r1 r3 r4 r6 net data phy D D app pre ses trans net data phy
Addressing & Network-level Routing Network Node 1 1,2,3,4 2 1,2 3 1,2,3,4 1.2 1.3 1.4 2.2 1.1 2.1 3.1 3.2 3.3 3.4 Detination Network 1.0 1.1 2.0 2.1 3.0 2.1 1.0 2.2 2.0 2.2 3.0 3.1 Router Port
Efficient Routing Routing decisions based on table lookup Routing tables keep only network portion of addresses size proportional to number of networks not number of hosts Algorithm is efficient and easy to understand Easy to automate routing table update
경로결정영향요소 Bandwidth Delay Reliability Load MTU Hop Count money S 1 로직접가? 아니면 2, 3 으로가? 1 2 3 D OSPF : Bandwidth RIP : hop count IGRP : Bandwidth, Delay, Reliability, Load, MTU
Routing 관련 Keyword advertising 혹은 announcement neighbor next hop 주기적 update cost = function (metric factors) RIP 의 metric factor 는 hop count IGRP 의 metric factor 는 bandwidth, delay, reliability, load, MTU OSPF 의 metric factor 는 bandwidth partial update 및 full update metric factor 및 metric cost Autonomous System Number (AS Number, ASN)
IP Routing 설정절차 Global Configuration IP routing protocol 중에하나를선택 Routing Update 에참여할자신의 Interface 에할당된 IP Network Address 선언 Interface Configuration IP Address 및 netmask 지정 RIP RIP / IGRP IGRP netb netd A B C neta netc nete
IP Routing Static Route vs. Dynamic Route Static Routing Static Route Default Route Dymanic Routing Interior Gateway Protocll RIP, IGRP(cisco), OSPF, EIGRP(cisco) Exterior Gateway Protocol BGP 라우터는 Static Route 및 Dynamic Route 를 Routing Table 에관리 라우터는동시에여러개의 Routing Protocol 을운영할수있음
Static routing
Dynamic routing Distance vector routing Link-state shortest-path-first routing link-state algorithm Dijkstra shortest-path-first algorithm Hierarchical routing Classless inter-domain routing Tunneling broadcasting routing reverse path forwarding spanning tree broadcast Multicast routing
Route & Routing Protocol Dynamic Route vs Static Route Dynamic Routing Protocol Distance Vector <-> Link State 주기적 update <-> 변화시즉시 update Singleprotocol <-> Multiprotocol IP, IPX 를동시에처리불능 <-> 동시처리가능 Interior <-> Exterior 네트웍그룹내 <-> 외부네트웍그룹간 Singlepath <-> Multipath Cost 가다른 link 를동시에이용하지않음 <-> 동시에이용함 Hierarachical <-> Flat 계층적인정보교환 <-> 계층적이지않음
Distance Vector Routing Protocol vs. Link State Routing Protocol Distance Vector 인접한라우터의관점으로전체네트웍정보를얻음 인접한라우터가갖고있는 cost 와인접한라우터까지의 cost 를더함 주기적으로정보를 update convergence time 이길다 Routing Table 을인접한라우터에게전달 Link State 각라우터가전체네트웍상태판단 자신이직접목적지까지의 cost 를계산함 변화즉시정보를 update convergence time 이짧다 변화된정보만을다른라우터들에게전달
RIP (Routing Information Protocol) RIP 은 RFC1058 에규정되어있다. RIP 은 BSD UNIX 의 routed 로처음발표되었었다. distance vector routing protocol interior gateway protocol metric factor 로 hop count 를이용하며가능한최대값은 15. sing path routing protocol 이다.
IGRP(Internet Gateway Routing Protocol) IGRP 는 cisco 사에서개발한것임. distance vector routing protocol interior gateway protocol metric factor 로 bandwidth, delay, reliability, load, mtu 를이용한다. 90 초마다 routing information 을전달한다. 추가적으로네트웍의변화를인지했을경우이를인접한라우터에게즉시전달해준다. 이런것을 Flash Update 라고한다. 이러한특성때문에 convergence time 이 rip 보다빠르다 multi path routing protocol 이다. 그렇지만기본적으로 single path routing 으로설정되어있으므로 multi path routing 을할수있도록설정해주어야한다.
OSPF(Open Shortest Path First) a routing protocol developed for Internet Protocol (IP) networks by the Interior Gateway Protocol (IGP) working group of the Internet Engineering Task Force (IETF) published as Request For Comments (RFC) 1247 was formed in 1988 to design an IGP based on the Shortest Path First (SPF) algorithm for use in the Internet Similar to the Interior Gateway Routing Protocol (IGRP) was created because in the mid-1980s, the Routing Information Protocol (RIP) was increasingly incapable of serving large, heterogeneous internetworks. a link-state routing protocol, contrasts with RIP and IGRP
. Exterior Gateway Protocol (EGP) - 외부 Gateway 프로토콜은 RFC-904 에문서화되어있고, RFC- 827 과 RFC-888 로대표되던초기의문안을개정
Router 구성 RAM 실행명령어 program bootstrap program IOS(Internetwork OS) active config file tables buffers NVRAM Flash backup config file IOS ROM bootstrap program subset IOS Interfaces LAN Interfaces (e, t, f) WAN Interfaces (s, hssi) Console Auxiliary
Router 환경설정수단 Console 이용 (async serial port) Auxiliary 이용 (auxiliary async serial port) LAN, WAN Interface를통한virtual terminal 이용 (telnet) TFTP 서버를이용 NMS 를이용 console virtual terminal virtual terminal auxiliary modem TFTP server NMS
Console 을이용한라우터접근 console Router con0 is now available Press RETURN to get started User Access Verification Password: Router> Router>enable Password: Router# Router#disable Router> Router>quit user mode prompt previledged mode prompt
라우터상태조회명령어 Router#show version Router#show process [cpu] Router#show protocols 실행명령어 program RAM bootstrap program IOS(Internetwork OS) active config file tables buffers NVRAM Flash ROM backup config file IOS bootstrap program subset IOS Router#show running-config Interfaces LAN Interfaces (e, t, f) WAN Interfaces (s, hssi) Console Auxiliary Router#show memory Router#show stacks Router#show buffers Router#show interface Router#show interface serial 0 Router#show flash Router#show startup-config Router#show config
Hierarchical routing over the Internet
Tunneling Example
9.7 ICMP Internet control message protocol an integral part of all IP implementation Used mostly by routers to report delivery or routing problems to original source Uses IP to carry control messages main functions error reporting reachability testing congestion control route-change notification performance measuring subnet addressing
ICMP messages Error reporting Destination Unreachable Time Exceeded Parameter error Reachability testing Echo Request/Reply Congestion Control Source Quench Route exchange Redirect (change route) Performance measuring Time-stamp request/reply Subnet addressing Address Mast Request/Reply
ICMP Message Encapsulation Type Code Checksum UNUSED (Must be Zero) Internet header + 64 bits of data ICMP message IP header IP data Frame header Frame data ICMP message has header and data areas Complete ICMP message is treated as data in IP datagram Complete IP datagram is treated as data in physical network frame
9.8 QoS support To meet more varies set of QoS requirements IntServ : integrated services DiffServ : differentiated services type of service field in IP packer header be used by routers
Integrated services Three different classes service in IntServ solution guaranteed class a specified Max. delay and jitter an assured level of bandwidth» are guaranteed for application involving the playout of real-time streams controlled load (as predictive) class no firm guarantees are provided a constant level of service equivalent to that obtained with the best-effort service at light loads for application involving real-time streams that have the capability of adjusting the amount of real-time data best-effort for text-based applications
Control mechanisms for QoS Token bucket filter an amount of buffer/queue space is reserved for each flow in a container called a bucket token: the quaranteed QoS requirements Weighted fair queuing a queue management to ensure the quaranteed QoS requirements compares the time-stamp of the packet Random early detection a queue management to ensure the quaranteed QoS requirements compare the queue length Resource reservation protocol (RSVP)
RSVP principles
RSVP 에서의데이터흐름
DiffServ
9.9 PPP link layer PSTN Cloud Intranet Cloud PPP NAS User (Client) Private Network IP connection 전통적인 Dial-up Service Layer 2 Mode Layer 3 Mode IP L2TP PPP IPX IP VTP IPX Link Layer Frame Layer 3 Protocol Tunneling Pakcet Format
Layer 2 Mode and Layer 3 Mode
PPTP Installation Process