Introduction and Overview

Transcription

1 Chapter 1 Itroductio ad Overview 1.1 Opportuities Offered by The Iteret Protocol versio 6 () is ow gaiig mometum as a improved etwork layer protocol. There is much commercial iterest ad activity i Europe ad Asia, ad as of press time, there also was some tractio i the Uited States. For example, the U.S. Departmet of Defese (DoD) aouced that from October 1, 2003, all ew developmets ad procuremets eeded to be -capable; the DoD s goal was to complete the trasitio to for all itra- ad iteretworkig across the agecy by I 2005, the U.S. Geeral Accoutability Office (GAO) recommeded that all agecies become proactive i plaig a coheret trasitio to. The expectatio is that i the ext few years a trasitio to this ew protocol will occur worldwide. is cosidered to be the ext-geeratio Iteret Protocol [HUI199701], [HAG200201], [MUR200501], [SOL200401], [ITO200401], [MIL199701], [MIL200001], [GRA200001], [DAV200201], [LOS200301], [LEE200501], [GON199801], [DEM200301], [GOS200301], [MIN200601], ad [WEG199901]. The curret versio of the Iteret Protocol, IPv4, has bee i use for almost 30 years ad exhibits some challeges i supportig emergig demads for address space cardiality, high-desity mobility, multimedia, ad strog security. This is particularly true i developig domestic ad defese departmet applicatios utilizig peer-to-peer etworkig. is a improved versio of the Iteret Protocol that is desiged to coexist with IPv4 ad evetually provide better iteretworkig capabilities tha IPv4 [IPV200401]. 1 AU8516.idb 1 10/31/07 10:02:48 AM

2 2 Hadbook of IPv4 to Trasitio offers the potetial of achievig the scalability, reachability, ed-to-ed iterworkig, quality of service (QoS), ad commercial-grade robustess for data as well as for Voice over IP (VoIP), IP-based TV (IPTV) distributio, ad tripleplay etworks; these capabilities are madatory mileposts of the techology if it is to replace the time divisio multiplexig (TDM) ifrastructure aroud the world. was iitially developed i the early 1990s because of the aticipated eed for more ed-system addresses based o aticipated Iteret growth, ecompassig mobile phoe deploymet, smart home appliaces, ad billios of ew users i developig coutries (e.g., Chia ad Idia). New techologies ad applicatios such as VoIP, always-o access (e.g., Digital Subscriber Lie ad cable), Etheret to the home, coverged etworks, ad evolvig ubiquitous computig applicatios will be drivig this eed eve more i the ext few years [IPV200501]. Figure 1.1 depicts oe example of a coverged etwork utilizig, with both local ad wide area compoets as well as private ad carrier-provided commuicatios domais; the /IPv4 etwork show i this figure supports video delivery, VoIP, Iteret, itraet, ad wireless services. Basic etwork address traslatio (NAT) is a method by which IP addresses (specifically IPv4 addresses) are trasparetly mapped from oe group to aother. Specifically, private oregistered addresses are mapped to a small set (as small as oe) of public registered addresses; this impacts the geeral addressability, accessibility, ad idividuality of the device. Network address port traslatio (NAPT) is a method by which may etwork addresses ad their TCP/UDP (Trasmissio Cotrol Protocol/User Datagram Protocol) ports are traslated ito a sigle etwork address ad its TCP/UDP ports. Together, these two methods, referred to as traditioal NAT, provide a mechaism to coect a realm with private addresses to a exteral realm with globally uique registered addresses [RFC3022]. NAT is a short-term solutio for the aticipated Iteret growth pheomeo, ad a better solutio is eeded for address exhaustio. There is a recogitio that NAT techiques make the Iteret, the applicatios, ad eve the devices more complex; this meas a cost overhead [IPV200501]. The expectatio is that ca make IP devices less expesive, more powerful, ad eve cosume less power. The power issue is importat ot oly for evirometal reasos, but also for improved operability (e.g., loger battery life i portable devices, such as mobile phoes). Corporatios ad govermet agecies will be able to achieve a umber of improvemets with. ca improve a firm s itraet, with beefits such as the followig: Expaded addressig capabilities Server-less autocofiguratio ( plug-ad-play ) ad recofiguratio IPTV is the delivery of (etertaimet-quality) video programmig over a IP-based etwork. Traditioal telecom carriers are lookig to compete with cable TV compaies by deployig IP video services over their etworks. AU8516.idb 2 10/31/07 10:02:48 AM

3 Itroductio ad Overview 3 E911 CCSS7 Video Cable TV Network (VoIP) ATM/IP Iteret VoIP Gateway CCSS7 E911 ENUM Server (Directory) PSTN IP Phoe IP Phoe IP Phoe CCSS7 E911 Wireless Network (VoIP) CCSS7 Traditioal Telephoy SIP Iteret Pure Play IP # 1 Broadbad Coectio (DSL, Cable, etc.) E911 Voice/Data Cliet Applicatio Servers Directory Pure Play IP # 2 /IPv4 Etheret IP Phoe /IPv4 Pure Play IP # 3 Switched Etheret LAN H.323, SIP Call Server/ SIP Proxy Iteret Remote IP Phoe VoIP Gateway Proxy (e.g. XML Firewall) Remote IP Phoe Firewall Compay X Mai Site Network Router Itraet Core Remote IP Phoes (e. q. MPLS) Remote IP Phoes Compay X Secodary Site Remote IP Phoes Compay X Brach Locatio Compay X Brach Locatio IPv4 Remote IP Phoes Compay Y Bbrach Locatio Voice/Data Cliet Applicatio Servers Directory IPv4 Etheret IP Phoe H.323, SIP Call Server/ SIP Proxy Switched Etheret LAN PSTN VoIP Gateway IPv4 Proxy (e.g., XML Firewall) Compay Y Mai Site IPv4 Network Router Itraet Core Remote IP Phoes IPv4 Romote IP Phoes Compay X Brach Locatio Compay Y Secodary Site Figure 1.1 Example of the use of, with emphasis o coverged etworks. AU8516.idb 3 10/31/07 10:03:26 AM

4 4 Hadbook of IPv4 to Trasitio More efficiet ad robust mobility mechaisms Ed-to-ed security, with built-i, strog IP-layer ecryptio ad autheticatio Streamlied header format ad flow idetificatio Ehaced support for multicast ad QoS Extesibility, with improved support for feature optios or extesios Although the basic fuctio of the Iteret Protocol is to move iformatio across etworks, has more capabilities built ito its foudatio tha IPv4. A key capability is the sigificat icrease i address space. For example, all devices could have a public IP address so that they ca be uiquely tracked. Today, ivetory maagemet of dispersed IT assets caot be achieved with IP mechaisms; durig the ivetory cycle, someoe has to maually verify the locatio of each desktop computer. With, oe ca use the etwork to verify where such equipmet is; eve o-it equipmet i the field ca also be tracked by havig a IP address permaetly assiged to it. also has extesive automatic cofiguratio (autocofiguratio) mechaisms ad reduces the IT burde, makig cofiguratio essetially plug-ad-play. Corporatios ad istitutios eed to start plaig the migratio process ad determiig best how coexistece ca be maitaied durig the three- to six-year widow that will likely be required to achieve the global worldwide trasitio. This book addresses the migratio ad macro-level scalability requiremets. 1.2 Itroductory Overview of The Iteret Protocol was desiged i the 1970s to coect computers that were i separate geographic locatios. Computers i a campus were coected by local etworks, but these local etworks were separated ito essetially stad-aloe islads. Iteret, as a ame to desigate the protocol ad more recetly the worldwide iformatio etwork, simply meas iteretwork, that is, a coectio betwee etworks. I the begiig, the protocol had oly military use, but computers from uiversities ad eterprises were quickly added. The Iteret as a worldwide iformatio etwork is the result of the practical applicatio of the IP, that is, the result of the itercoectio of a large set of iformatio etworks [IPV200501]. Startig i the early 1990s, developers realized that the commuicatio eeds of the 21st cetury icluded a protocol with some ew features ad capabilities while retaiig the useful features of the existig protocol. Although lik-level commuicatio does ot geerally require a ode idetifier (address) because the device is itrisically idetified with the lik-level address, commuicatio over a group of liks (a etwork) does require uique ode idetifiers (addresses). The IP address is a idetifier that is applied to each device coected to a IP etwork. I this setup, differet elemets takig part i the etwork AU8516.idb 4 10/31/07 10:03:27 AM

5 Itroductio ad Overview 5 (servers, routers, user computers, etc.) commuicate amog each other usig their IP address as a etity idetifier. I versio 4 of the IP, addresses cosist of four octets. For ease of huma coversatio, IP addresses are represeted as separated by periods, for example, , with the decimal umbers shorthad for (ad correspodig to) the biary code described by the byte i questio (a eight-bit umber takes a value i the rage). Because the IPv4 address has 32 bits, there are omially 2 32 differet IP addresses (approximately four billio odes, if all combiatios are used). is the Iteret s ext-geeratio protocol, which was at first called IPg (Iteret Next Geeratio). The Iteret Egieerig Task Force (IETF) developed the basic specificatios durig the 1990s to support a migratio to a ew eviromet. is defied i RFC (Request for Commet) 2460, Iteret Protocol, Versio 6 () Specificatio, by S. Deerig ad R. Hide (December 1998) [RFC2460], which makes obsolete RFC (IP versio 5 was employed for aother use, a experimetal real-time streamig protocol, ad to avoid ay cofusio, it was decided ot to use this omeclature.) Beefits IPv4 has prove, by meas of its log life, to be a flexible ad powerful etworkig mechaism. However, IPv4 is startig to exhibit limitatios, ot oly with respect to the eed for a icrease of the IP address space, drive, for example, by ew populatios of users i coutries like Chia ad Idia ad by ew techologies with always-coected devices (DSL, cable, etworked persoal digital assistats [PDAs], 2.5G/3G mobile telephoes, etc.), but also i referece to a potetial global rollout of VoIP. creates a ew IP address format so that the umber of IP addresses will ot be exhausted for several decades or loger eve though a etire ew crop of devices is expected to coect to Iteret. also adds improvemets i areas such as routig ad etwork autocofiguratio. Specifically, ew devices that coect to Iteret will be plug-ad-play devices. With, oe is ot required to cofigure dyamic opublished local IP addresses, the gateway address, the subetwork mask, or ay other parameters. The equipmet, whe plugged ito the etwork, automatically obtais all requisite cofiguratio data [IPV200501]. The advatages of ca be summarized as follows: Scalability: has 128-bit addresses versus 32-bit IPv4 addresses. With IPv4, the theoretical umber of available IP addresses is 2 32 ~ offers a space. Hece, the umber of available uique ode addressees is ~ Security: icludes security features, such as payload ecryptio ad autheticatio of the source of the commuicatio, i its specificatios. AU8516.idb 5 10/31/07 10:03:27 AM

6 6 Hadbook of IPv4 to Trasitio Real-time applicatios: To provide better support for real-time traffic (e.g., VoIP), icludes labeled flows i its specificatios. By meas of this mechaism, routers ca recogize the ed-to-ed flow to which trasmitted packets belog. This is similar to the service offered by Multi-Protocol Label Switchig (MPLS), but it is itrisic with the IP mechaism rather tha a add-o. Also, it preceded this MPLS feature by a umber of years. Plug-ad-play: icludes a plug-ad-play mechaism that facilitates the coectio of equipmet to the etwork. The requisite cofiguratio is automatic. Mobility: icludes more efficiet ad ehaced mobility mechaisms, particularly importat for mobile etworks. Optimized protocol: embodies IPv4 best practices but removes uused or obsolete IPv4 characteristics. This results i a better-optimized Iteret Protocol. Addressig ad routig: improves the addressig ad routig hierarchy. Extesibility: has bee desiged to be extesible ad offers support for ew optios ad extesios Traditioal Addressig Classes for IPv4 With IPv4, the 32-bit address ca be represeted as AdrClass etid hostid. The etwork portio ca cotai either a etwork ID or a etwork ID ad a subet. Every etwork ad every host or device has a uique address by defiitio. Figure 1.2 depicts the traditioal address classes. Traditioal Class A Address. Class A uses the first bit of the 32-bit space (bit 0) to idetify it as a Class A address; this bit is set to 0. Bits 1 to 7 represet the etwork ID, ad bits 8 through 31 idetify the persoal computer (PC), termial device, or host/server o the etwork. This address space supports = 126 etworks ad approximately 16 millio devices (2 24 ) o each etwork. By covetio, the use of a all 1s or all 0s address for both the etwork ID ad the host ID is prohibited (which is the reaso for subtractig the 2 i the equatio). Traditioal Class B Address. Class B uses the first 2 bits (bit 0 ad bit 1) of the 32-bit space to idetify it as a Class B address; these bits are set to 10. Bits 2 to 15 represet the etwork ID, ad bits 16 through 31 idetify the PC, termial device, or host/server o the etwork. This address space supports = 16,382 etworks ad = 65,134 devices o each etwork. Traditioal Class C Address. Class C uses the first 3 bits (bit 0, bit 1, ad bit 2) of the 32-bit space to idetify it as a Class C address; these bits are set AU8516.idb 6 10/31/07 10:03:27 AM

7 Itroductio ad Overview 7 Class A Network ID Host ID Class B Network ID Host ID Class C Host ID Class D Multicast Address Figure 1.2 Traditioal address classes for IP address. to 110. Bits 3 to 23 represet the etwork ID, ad bits 24 through 31 idetify the PC, termial device, or host/server o the etwork. This address space supports about 2 millio etworks (2 21 2) ad = 254 devices o each etwork. Traditioal Class D Address. This class is used for broadcastig i which all devices o the etwork receive the same packet. Class D uses the first 4 bits (bit 0, bit 1, bit 2, ad bit 3) of the 32-bit space to idetify it as a Class D address; these bits are set to This is used i IP Multicast applicatios (for example for IPTV). Classless iterdomai routig (CIDR), described i RFC 1518, RFC 1519, ad RFC 2050, is yet aother mechaism that was developed to help alleviate the problem of exhaustio of IP addresses ad growth of routig tables. The cocept behid CIDR is that blocks of multiple addresses (e.g., blocks of Class C addresses) ca be combied, or aggregated, to create a larger classless set of IP addresses with more hosts allowed. Blocks of Class C etwork umbers are allocated to each etwork service provider; orgaizatios usig the etwork service provider for Iteret coectivity are allocated subsets of the service provider s address space as required. These multiple Class C addresses ca the be summarized i routig tables, resultig i fewer route advertisemets. The CIDR mechaism ca also be applied to blocks of Class A ad B addresses [TEA200401]. All of this assumes, however, that the istitutio i questio already has a assiged set of public, registered IP addresses; it does ot address the issue of how to get additioal public, registered globally uique IP addresses. AU8516.idb 7 10/31/07 10:03:28 AM

8 8 Hadbook of IPv4 to Trasitio Network Address Traslatio Issues i IPv4 IPv4 addresses ca be from a officially assiged public rage or from a iteral itraet private (but ot globally uique) block. Iteral itraet addresses may be i the rages /8, /12, ad /16. I the iteral itraet private address case, a NAT fuctio is employed to map the iteral addresses to a exteral public address whe the private-to-public etwork boudary is crossed. This imposes a umber of limitatios, particularly because the umber of registered public addresses available to a compay is almost ivariably much smaller (as small as oe) tha the umber of iteral devices requirig a address. As oted, IPv4 theoretically allows up to 2 32 addresses, based o a four-octet address space. Public, globally uique addresses are assiged by the Iteret Assiged Numbers Authority (IANA). IP addresses are addresses of etwork odes at Layer 3; each device o a etwork (whether the Iteret or a itraet) must have a uique address. I IPv4, it is a 32-bit (four-byte) biary address used to idetify the device. It is represeted by the omeclature a.b.c.d (with each of a, b, c, ad d from 1 to 255; 0 has a special meaig). Examples are , , ad The problem is that durig the 1980s may public, registered addresses were allocated to firms ad orgaizatios without ay cosistet cotrol. As a result, some orgaizatios have more addresses tha they actually eed, givig rise to the preset dearth of available registerable Layer 3 addresses. Furthermore, ot all IP addresses ca be used due to the fragmetatio described. Oe approach to the issue would be reumberig ad reallocatio of the IPv4 addressig space. However, this is ot as simple as it appears because it requires worldwide coordiatio efforts. Moreover, it would still be limited for the huma populatio ad the quatity of devices that will be coected to the Iteret i the medium-term future [IPV200501]. At this jucture, ad as a temporary ad pragmatic approach to alleviate the dearth of addresses, NAT mechaisms are employed by orgaizatios ad eve home users. This mechaism cosists of usig oly a small set of public IPv4 addresses for a etire etwork to access the Iteret. The myriad iteral devices are assiged IP addresses from a specifically desigated rage of Class A or Class C addresses that are locally uique but are duplicatively used ad reused withi various orgaizatios. I some cases (e.g., residetial Iteret access use via DSL or cable), the legal IP address is oly provided to a user o a time-lease basis rather tha permaetly. A umber of protocols caot travel through a NAT device, ad hece the use of NAT implies that may applicatios (e.g., VoIP) caot be used effectively i all istaces. As a cosequece, these applicatios ca oly be used i itraets. Examples iclude [IPV200501] the followig: Multimedia applicatios such as videocoferecig, VoIP, or video-odemad/iptv do ot work smoothly through NAT devices. Multimedia AU8516.idb 8 10/31/07 10:03:28 AM

9 Itroductio ad Overview 9 applicatios make use of Real-Time Trasport Protocol (RTP) ad Real-Time Cotrol Protocol (RTCP). These i tur use UDP with dyamic allocatio of ports, ad NAT does ot directly support this eviromet. Kerberos autheticatio eeds the source address, ad the source address i the IP header is ofte modified by NAT devices. IPSec is used extesively for data autheticatio, itegrity, ad cofidetiality. However, whe NAT is used, there is a impact o IPSec because NAT chages the address i the IP header. Multicast, although possible i theory, requires complex cofiguratio i a NAT eviromet ad hece i practice is ot utilized as ofte as could be the case. The eed for obligatory use of NAT disappears with Address Space The format of addressig is described i RFC As oted, a address cosists of 128 bits rather tha 32 bits as with IPv4 addresses. The umber of bits correlates to the address space as follows: IP Versio Size of Address Space 128 bits, which allows for or 340,282,366,920,938,463,463,374,60 7,431,768,211,456 (3.4 ( ) possible addresses IPv4 32 bits, which allows for 2 32 or 4,294,967,296 possible addresses The relatively large size of the address is desiged to be subdivided ito hierarchical routig domais that reflect the topology of the moder-day Iteret. The use of 128 bits provides multiple levels of hierarchy ad flexibility i desigig hierarchical addressig ad routig. The IPv4-based Iteret curretly lacks this flexibility [MSD200401]. The address is represeted as eight groups of 16 bits each, separated by the : character. Each 16-bit group is represeted by four hexadecimal digits; that is, each digit has a value betwee 0 ad F (0, 1, 2, A, B, C, D, E, F with A = 10, B = 11, ad so o to F = 15). What follows is a address example: 3223:0BA0:01E0:D001:0000:0000:D0F0:0010 If oe or more four-digit groups is 0000, the zeros may be omitted ad replaced with colos (::). For example, 3223:0BA0:: is the abbreviated form of the followig address: 3223:0BA0:0000:0000:0000:0000:0000:0000 AU8516.idb 9 10/31/07 10:03:29 AM

10 10 Hadbook of IPv4 to Trasitio Similarly, the address 3223:0BA0::1234 is the abbreviated form of the followig address: 3223:0BA0:0000:0000:0000:0000:0000:1234 There is also a method to desigate groups of IP addresses or subetworks that is based o specifyig the umber of bits that desigate the subetwork, begiig from left to right, usig remaiig bits to desigate sigle devices iside the etwork. For example, the otatio 3223:0BA0:01A0::/48 idicates that the part of the IP address used to represet the subetwork has 48 bits. Because each hexadecimal digit has four bits, this poits out that the part used to represet the subetwork is formed by 12 digits, that is: 3223:0ba0:01a0. The remaiig digits of the IP address would be used to represet odes iside the etwork. There are a umber of special addresses: Autoretur or loopback virtual address. This address is specified i IPv4 as the address. I, this address is represeted as ::1. Uspecified address (::). This address is ot allocated to ay ode because it is used to idicate the absece of a address. over IPv4 dyamic/automatic tuel addresses. These addresses are desigated as IPv4-compatible addresses ad allow the sedig of traffic over IPv4 etworks i a trasparet maer. They are represeted as, for example, :: IPv4 over addresses automatic represetatio. These addresses allow for IPv4-oly odes to still work i etworks. They are desigated as IPv4-mapped addresses ad are represeted as ::FFFF:, for example, ::FFFF Basic Protocol Costructs Table 1.1 lists basic termiology (see Appedix A for a more iclusive glossary). Table 1.2 shows the core protocols that comprise (see Appedix B for a more iclusive listig). Like IPv4, is a coectioless, ureliable datagram protocol used primarily for addressig ad routig packets betwee hosts. Coectioless meas that a sessio is ot established before exchagig data. Ureliable meas that delivery is ot guarateed. always makes a best-effort attempt to deliver a packet. A packet might be lost, delivered out of sequece, duplicated, or delayed. AU8516.idb 10 10/31/07 10:03:29 AM

11 Itroductio ad Overview 11 Table 1.1 Basic Termiology Address Host Iterface Lik Lik-layer idetifier Lik-local address Multicast address Neighbor Node Packet Prefix Prefix legth Router Uicast address A IP layer idetifier for a iterface or a set of iterfaces. Ay ode that is ot a router. A ode s attachmet to a lik. A commuicatio facility or medium over which odes ca commuicate at the lik layer, that is, the layer immediately below IP. Examples are Etheret (simple or bridged); PPP liks, X.25, Frame Relay, ATM etworks ad Iteret (or higher) layer tuels, such as tuels over IPv4 or itself. A lik-layer idetifier for a iterface. Examples iclude IEEE 802 addresses for Etheret etwork iterfaces ad E.164 addresses for Itegrated Services Digital Network (ISDN) liks. A address havig a lik-oly scope, idicated by havig the prefix (FE80::/10), that ca be used to reach eighborig odes attached to the same lik. Every iterface has a lik-local address. A idetifier for a set of iterfaces typically belogig to differet odes. A packet set to a multicast address is delivered to all iterfaces idetified by that address. A ode attached to the same lik. A device that implemets IP. A IP header plus payload. The iitial bits of a address or a set of IP addresses that share the same iitial bits. The umber of bits i a prefix. A ode that forwards IP packets ot explicitly addressed to itself. A idetifier for a sigle iterface. A packet set to a uicast address is delivered to the iterface idetified by that address. per se does ot attempt to recover from these types of errors. The ackowledgmet of packets delivered ad the recovery of lost packets is doe by a higher-layer protocol, such as TCP [MSD200401]. From a packet-forwardig perspective, operates just like IPv4. A packet, also kow as a datagram, cosists of a header ad a payload, as show Figure 1.3. AU8516.idb 11 10/31/07 10:03:29 AM

12 12 Hadbook of IPv4 to Trasitio Table 1.2 Key Protocols Protocol Iteret Protocol versio 6 (): RFC 2460 Iteret Cotrol Message Protocol for (ICMPv6): RFC 2463 Multicast Listeer Discovery (MLD): RFC 2710, RFC 3590, RFC 3810 Neighbor Discovery (ND): RFC 2461 Descriptio is a coectioless datagram protocol used for routig packets betwee hosts. ICMPv6 is a mechaism that eables hosts ad routers that use commuicatio to report errors ad sed simple status messages. MLD is a mechaism that eables oe to maage subet multicast membership for. MLD uses a series of three ICMPv6 messages. MLD replaces the Iteret Group Maagemet Protocol (IGMP) versio 3 that is employed for IPv4. ND is a mechaism that is used to maage ode-to-ode commuicatio o a lik. ND uses a series of five ICMPv6 messages. ND replaces Address Resolutio Protocol (ARP), ICMPv4 Router Discovery, ad the ICMPv4 Redirect message. It also provides additioal fuctios. Packet Header Payload Figure 1.3 packet. The header cosists of two parts: the base header ad optioal extesio headers. Fuctioally, the optioal extesio headers ad upper-layer protocols (e.g., TCP) are cosidered part of the payload. Table 1.3 shows the fields i the base header. IPv4 ad headers are ot directly iteroperable: Hosts or routers must use a implemetatio of both IPv4 ad to recogize ad process both header formats. This gives rise to a umber of complexities i the migratio process betwee the IPv4 ad the eviromets. However, techiques have bee developed to hadle these migratios, as we discuss later i the book. AU8516.idb 12 10/31/07 10:03:30 AM

13 Itroductio ad Overview 13 Table 1.3 Base Header Header Field Legth (bits) Fuctio Versio 4 Idetifies the versio of the protocol. For, the versio is 6. Traffic Class 8 Iteded for origiatig odes ad forwardig routers to idetify ad distiguish betwee differet classes or priorities of packets. Flow Label 20 (Sometimes referred to as flow ID.) Defies how traffic is hadled ad idetified. A flow is a sequece of packets set either to a uicast or a multicast destiatio. This field idetifies packets that require special hadlig by the ode. The followig list shows the ways the field is hadled if a host or router does ot support flow label field fuctios: If the packet is beig set, the field is set to zero. If the packet is beig received, the field is igored. Payload Legth 16 Idetifies the legth, i octets, of the payload. This field is a 16-bit usiged iteger. The payload icludes the optioal extesio headers as well as the upper-layer protocols, for example, TCP. Next Header 8 Idetifies the header immediately followig the header. The followig are examples of the ext header: 00 = Hop-by-Hop optios 01 = ICMPv4 04 = IP i IP (ecapsulatio) 06 = TCP 17 = UDP 43 = Routig 44 = Fragmet 50 = Ecapsulatig security payload 51 = Autheticatio 58 = ICMPv6 AU8516.idb 13 10/31/07 10:03:30 AM

14 14 Hadbook of IPv4 to Trasitio Table 1.3 Base Header (cotiued) Header Field Legth (bits) Fuctio Hop Limit 8 Idetifies the umber of etwork segmets, also kow as liks or subets, o which the packet is allowed to travel before beig discarded by a router. The hop limit is set by the sedig host ad is used to prevet packets from edlessly circulatig o a iteretwork. Whe forwardig a packet, routers must decrease the hop limit by 1 ad must discard the packet whe the hop limit is 0. Source Address 128 Idetifies the address of the origial source of the packet. Destiatio Address 128 Idetifies the address of the itermediate or fial destiatio of the packet Autocofiguratio Autocofiguratio is a ew characteristic of that facilitates etwork maagemet ad system setup tasks by users. This characteristic is ofte called plug-adplay or coect-ad-work. Autocofiguratio facilitates iitializatio of user devices: After coectig a device to a etwork, oe or several globally uique addresses are automatically allocated. The autocofiguratio process is flexible, but it is also somewhat complex. The complexity arises from the fact that various policies are defied ad implemeted by the etwork admiistrator. Specifically, the admiistrator determies the parameters that will be assiged automatically. At a miimum (or whe there is o etwork admiistrator), the allocatio of a lik-local address is ofte icluded. The lik-local address allows commuicatio with other odes placed i the same physical etwork. Note that the word lik has somewhat of a special meaig i ; it idicates a commuicatio facility or medium over which odes ca commuicate at the lik layer, that is, the layer immediately below. Examples are Etherets (simple or bridged); PPP (Poit-to-Poit Protocol) liks; a X.25 packet-switched etwork; a Frame Relay etwork; Cell Relay/Asychroous Trasfer Mode (ATM) etwork; ad Iteret(workig) layer (or higher layer) tuels, such as tuels over IPv4 or itself [RFC2460]. AU8516.idb 14 10/31/07 10:03:30 AM

15 Itroductio ad Overview 15 Two autocofiguratio basic mechaisms exist: stateful ad stateless. Both mechaisms ca be used i a complemetary maer or simultaeously to defie parameter cofiguratios [IPV200501]. Stateless autocofiguratio is also described as serverless. Here, the presece of cofiguratio servers to supply profile iformatio is ot required. The host geerates its ow address usig a combiatio of the iformatio that it possesses (i its iterface or etwork card) ad the iformatio that is periodically supplied by the routers. Routers determie the prefix that idetifies etworks associated to the lik uder discussio. The iterface idetifier idetifies a iterface withi a subetwork ad is ofte, ad by default, geerated from the Media Access Cotrol (MAC) address of the etwork card. The address is built combiig the 64 bits of the iterface idetifier with the prefixes that routers determie as belogig to the subetwork. If there is o router, the the iterface idetifier is self-sufficiet to allow the PC to geerate a lik-local address. The lik-local address is sufficiet to allow the commuicatio betwee several odes coected to the same lik (the same local etwork). Stateful cofiguratio requires a server to sed the iformatio ad parameters of etwork coectivity to odes ad hosts. Servers maitai a database with all addresses allocated ad a mappig of the hosts to which these addresses have bee allocated, alog with ay iformatio related to all requisite parameters. I geeral, this mechaism is based o the use of Dyamic Host Cotrol Protocol versio 6 (DHCPv6). Stateful autocofiguratio is ofte employed whe there is a eed for rigorous cotrol i referece to the address allocated to hosts; i stateless autocofiguratio, the oly cocer is that the address be uique. Depedig o the etwork admiistrator policies, it may be required that some addresses be allocated to specific hosts ad devices i a permaet maer; here, the stateful mechaism is employed o this subset of hosts, but the cotrol of the remaiig parameters or odes could be less rigorous. I some eviromets, there are o policy requiremets o the importace of the allocated addresses, but there may be rules o the parameters, such as that they be allocated i a certai static maer, with iformatio stored i a server. addresses are leased to a iterface for a fixed established time (icludig a ifiite time). Whe this lifetime expires, the lik betwee the iterface ad the address is ivalidated, ad the address ca be reallocated to other iterfaces. For the suitable maagemet of address expiratio time, a address goes through two states (stages) whe it is affiliated to a iterface [IPV200501]: 1. At first, a address is i a preferred state, so its use i ay commuicatio is ot restricted. 2. After that, a address becomes deprecated, idicatig that its affiliatio with the curret iterface will (soo) be ivalidated. AU8516.idb 15 10/31/07 10:03:30 AM

16 16 Hadbook of IPv4 to Trasitio Whe i a deprecated state, the use of the address is discouraged, although it is ot forbidde. However, whe possible, ay ew commuicatio (e.g., the opeig of a ew TCP coectio) must use a preferred address. A deprecated address should oly be used by applicatios that already used it before ad if it is difficult to chage this address to aother address without causig a service iterruptio. To esure that allocated addresses (grated either by maual mechaisms or by autocofiguratio) are uique i a specific lik, the lik duplicated addresses detectio algorithm is used. The address to which the duplicated address detectio algorithm is applied is desigated (util the ed of this algorithmic sessio) as a attempt address. I this case, it does ot matter that such address has bee allocated to a iterface ad that received packets are discarded. Next, we describe how a address is formed. The lowest 64 bits of the address idetify a specific iterface, ad these bits are desigated as iterface idetifier. The highest 64 bits of the address idetify the path or the prefix of the etwork or router i oe of the liks to which such iterface is coected. The address is formed by combiig the prefix with the iterface idetifier. It is possible for a host or device to have ad IPv4 addresses simultaeously. Most of the systems that curretly support allow the simultaeous use of both protocols. I this way, it is possible to support commuicatio with IPv4- oly etworks as well as -oly etworks ad the use of the applicatios developed for both protocols [IPV200501]. It is possible to trasmit traffic over IPv4 etworks via tuelig methods. This approach cosists of wrappig the traffic as IPv4 payload data: traffic is set ecapsulated ito IPv4 traffic, ad at the receivig ed this traffic is parsed as traffic. Trasitio mechaisms are methods used for the coexistece of IPv4 or devices ad etworks. For example, a -i-ipv4 tuel is a trasitio mechaism that allows devices to commuicate through a IPv4 etwork. The mechaism cosists of creatig the packets i a ormal way ad ecapsulatig them i a IPv4 packet. The reverse process is udertake i the destiatio machie, which deecapsulates the packet. There is a sigificat differece betwee the procedures to allocate IPv4 addresses, which focus o the parsimoious use of addresses (because addresses are a scarce resource ad should be maaged with cautio), ad the procedures to allocate addresses, which focus o flexibility. Iteret Service Providers (ISPs) deployig systems follow the Regioal Iteret Registries (RIRs) policies relatig to how to assig addressig space amog their cliets. RIRs are recommedig ISPs ad operators allocate to each cliet a /48 subetwork; this allows cliets to maage their ow subetworks without usig NAT. (The implicatio is that the eed for NAT disappears i.) To allow its maximum scalability, uses a approach based o a basic header, with miimum iformatio. This differetiates it from IPv4, i which differet optios are icluded i additio to the basic header. uses a header AU8516.idb 16 10/31/07 10:03:31 AM

17 Itroductio ad Overview 17 cocateatio mechaism to support supplemetary capabilities. The advatages of this approach iclude the followig: The size of the basic header is always the same ad is well kow. The basic header has bee simplified compared with IPv4 because oly eight fields are used istead of twelve. The basic header has a fixed size; hece, its processig by odes ad routers is more straightforward. Also, the header s structure aligs to 64 bits, so that ew ad future processors (64 bits miimum) ca process it i a more efficiet way. Routers placed betwee a source poit ad a destiatio poit (that is, the route that a specific packet has to pass through) do ot eed to process or uderstad ay followig headers. I other words, i geeral, iterior (core) poits of the etwork (routers) oly have to process the basic header; i IPv4, all headers must be processed. This flow mechaism is similar to the operatio i MPLS yet precedes it by several years. There is o limit to the umber of optios that the headers ca support (the basic header is 40 octets i legth; the IPv4 oe varies from 20 to 60 octets, depedig o the optios used). I, iterior/core routers do ot perform packet fragmetatio, but the fragmetatio is performed ed to ed. That is, source ad destiatio odes perform, by meas of the stack, the fragmetatio of a packet ad the reassembly, respectively. The fragmetatio process cosists of dividig the source packet ito smaller packets or fragmets [IPV200501]. A jumbogram is a optio that allows a packet to have a payload greater tha 65,535 bytes. Jumbograms are idetified with a 0 value i the payload legth i the header field ad iclude a Jumbo Payload Optio i the Hop-by-Hop Optio header. It is aticipated that such packets will be used i particular for multimedia traffic. This prelimiary overview of highlights the advatages of the ew protocol ad its applicability to a whole rage of applicatios, icludig VoIP. 1.3 Migratio ad Coexistece Migratio is expected to be fairly complex. Iitially, iteretworkig betwee the two eviromets will be critical. Existig IPv4 edpoits or odes will eed to ru dual-stack odes or covert to systems. Fortuately the ew protocol supports IPv4-compatible addresses, which is a address format that employs embedded IPv4 addresses. Tuelig, which we already described i passig, will play a major role i the begiig. There are a umber of requiremets that are typically applicable to a orgaizatio wishig to itroduce a service [6NE200501]: AU8516.idb 17 10/31/07 10:03:31 AM