IPv6+Happy+Eyeballs+-+IPv6+Fallback+解决方案介绍

IPv6HappyEyeballs朱彥如中華電信研究所2011.1117/2IPv4/IPv6Fallback(1/2)„許多作業系統及應用程式，在啟動dual-stack狀態下，會優先選擇選擇IPv6連線，如果失敗，再嘗試IPv4連線(Fallback)„相較於IPv4，目前IPv6網路品質尚未十分穩定„DNSserver包含未更新的資訊„Broken6to4orTeredotunnels„BrokenIPv6peering„…„啟動IPv6的用戶會比IPv4-only用戶經歷更多的連線延遲，造成啟動IPv6之意願降低„Vista/Win7在僅有6to4IPv6位址的狀況下，會先選用IPv4連線，以改善TCPfallback問題217/3IPv4/IPv6Fallback(2/2)資料來源:IETF17/4ExamplesofIPv4/IPv6Fallback(1/3)2001:ca0:1:100:11c4:7e56:6a58:cbb3202.39.142.150DaulStackDualStack:180:3::7202.39.224.717/5ExamplesofIPv4/IPv6Fallback(2/3)„MozillaFirefox7.01約21秒17/6ExamplesofIPv4/IPv6Fallback(3/3)„IE9.01約21秒17/7何為HappyEyeballs?„HappyeyeballsAlgorithm嘗試解決使用者轉移到雙堆疊時可能面臨的連線延遲Keepsyoureyeballshappy„目前正在IETFv6ops工作小組討論中„HappyEyeballs:SuccesswithDual-StackHosts,draft-ietf-v6ops-happy-eyeballs-0517/8PossibleSolutions„DNSwhitelist„Scalability不好„numberofDNSservers„numberofcontentproviders„無法及時反應網路瞬斷„ICPs選擇性開放其IPv6服務„由應用程式自行嘗試改善:Happy-eyeballsalgorithm„MoreaggressivelymakingconnectionsonIPv6andIPv4„增加的traffic不可造成網路/伺服器的服務品質大幅降低„Thehost'saddresspreferencemustbehonored„Requirementsforthealgorithmsarespecified17/9GoogleDNSWhitelistforIPv6資料來源:Google17/10GoalsofaHappyEyeballsAlgorithm„Providesfastconnectionforusers„先嘗試以IPv6連線，若短時間內不成功，則轉用IPv4連線„Avoidsthrashingthenetwork„避免老是同時嘗試IPv6及IPv4連線„Client端必須判斷IPv6或/及IPv4連線是否成功，並保留相關訊息，以避免多餘的連線嘗試17/11SuggestedHappyEyeballsAlgorithms(1/3)„AIPv6-BrokencaseTheclient同時透過IPv6/IPv4發送TCPSYNsTheclient會獲悉目的地的IPv4及IPv6連線是否成功，並保留此訊息以避免後續再進行多餘的連線嘗試17/12SuggestedHappyEyeballsAlgorithms(2/3)„AIPv6-WorkingCase17/13SuggestedHappyEyeballsAlgorithms(3/3)„如果IPv4/IPv6的選擇僅取決於連線速度，IPv4load仍會持續加重„ImplementationsMUSTpreferthefirstIPAFreturnedbythehost'saddresspreferencepolicy,unlessimplementingaastatefulstatefulalgorithmalgorithm„一般會優先選用IPv6，不過可以透過設定來更改„Ifthehost'spolicyisunknownornotattainable,implementationsMUSTpreferIPv6overIPv4„Thestatefulalgorithm-會記住IPv6連線或某些prefixes的IPv6連線老是失敗„後續連線可以透過成功的協定來進行„必須偶而切回原先喜好的協定進行連線17/14Examplealgorithms„InGoogleChromeandMozillaFirefox1.Callgetaddinfo(),whichreturnsalistofIPaddressessortedbythehost'saddresspreferencepolicy.2.Initiateaconnectionattemptwiththefirstaddressinthatlist(e.g.,IPv6).3.Ifthatconnectiondoesnotcompletewithinashortperiodoftime(e.g.,200-300ms),initiateaconnectionattemptwiththefirstaddressbelongingtotheotheraddressfamily(e.g.,IPv4)4.Thefirstconnectionthatisestablishedisused.Theotherconnectionisdiscarded.17/15Happy-EyeballsofChrome„為了配合WorldIPv6Day活動，Chrome11開始加入相關機制„Chrome14.0.8.35.2020.3秒17/16觀察與結論„HappyeyeballsAlgorithm嘗試解決使用者轉移到雙堆疊時可能面臨的連線延遲，同時仍讓IPv6保有優先連線權„為支援HappyEyeballs，應用軟體必須配合做修改，目前僅知ChromeWebBrowser支援„Happyeyeballsalgorithm多少還是會增加網路及伺服器的負擔，尤其當preferredAF(一般為IPv6)無法快速完成時„為了網路維運(如debugging及troubleshooting),支援軟體可以提供關掉HappyEyeballs的機制„預期只要網際網路仍有雙堆疊用戶，甚至IPv4-only伺服器，HappyEyeballsalgorithm將會繼續運作17/17ThankYouQ&A