IP路由高級(jí)技術(shù)(-).ppt

2019/7/11,Yang Wu-Jun,xian Institute of Post and Telecommuniations,1,IP路由協(xié)議（一）,NE實(shí)驗(yàn)室，2008 西安郵電學(xué)院,2019/7/11,Yang Wu-Jun,xian Institute of Post and Telecommuniations,2,什么是路由（ Routing）?,路由是將一個(gè)分組從一個(gè)位置轉(zhuǎn)發(fā)到另一個(gè)位置的過程。 在計(jì)算機(jī)網(wǎng)絡(luò)中，路由器轉(zhuǎn)發(fā)分組的目的地用一個(gè)邏輯地址表示。 路由器的兩個(gè)基本功能: Routing 學(xué)習(xí)網(wǎng)絡(luò)的拓?fù)浣Y(jié)構(gòu)構(gòu)造路由表 Forwarding 將分組從入端口轉(zhuǎn)發(fā)到去往目的地的出端口,2019/7/11,Yang Wu-Jun,xian Institute of Post and Telecommuniations,3,執(zhí)行路由功能的需要哪些信息,設(shè)備上必須有相應(yīng)的路由協(xié)議組件 路由設(shè)備必須知道相應(yīng)的目的網(wǎng)絡(luò) 路由表上是否有相應(yīng)的路由項(xiàng)? 路由當(dāng)前是否可用? 哪一個(gè)出端口代表最佳路徑? 擁有最小 metric值的路徑優(yōu)先 等值路徑則負(fù)荷分擔(dān),2019/7/11,Yang Wu-Jun,xian Institute of Post and Telecommuniations,4,路由信息,大部分路由信息都已經(jīng)包含在路由表中！,rip 100/118654 via , 00:00:23, Fei-0/1,rip - How the route was learned (rip) - Destination logical network or subnet 100 - Administrative distance (trustworthiness factor) /118654 - Metric value (reachability) via - Next-hop logical address (next router) 00:00:23 - Age of entry (in hours:minutes:seconds) Fei-0/1 - Interface through which the route was learned and through which the packet will leave,2019/7/11,Yang Wu-Jun,xian Institute of Post and Telecommuniations,5,管理距離（Administrative Distance）,管理距離 提供了一種路由協(xié)議的選擇方式 管理距離越小, 則路由的可信度越高 手工輸入的靜態(tài)路由由于通過路由協(xié)議學(xué)到的動(dòng)態(tài)路由 使用復(fù)雜 metrics計(jì)算方式的路由協(xié)議優(yōu)先級(jí)高于計(jì)算簡(jiǎn)單的路由協(xié)議,2019/7/11,Yang Wu-Jun,xian Institute of Post and Telecommuniations,6,管理距離實(shí)例表,2019/7/11,Yang Wu-Jun,xian Institute of Post and Telecommuniations,7,路由選擇,路由協(xié)議為每個(gè)目的網(wǎng)絡(luò)保持一條無環(huán)路的路徑 路由和metric值一起在路由器間廣播 到一個(gè)目的網(wǎng)絡(luò)路徑的metric值等于由構(gòu)成該路徑的所有中間鏈路的metric值之和 選路過程就是根據(jù)metric值選擇一條到目的網(wǎng)絡(luò)的最優(yōu)路徑。 假如到同一目的網(wǎng)絡(luò)存在多條路徑Metric值相等，則可以使用多路徑。,2019/7/11,Yang Wu-Jun,xian Institute of Post and Telecommuniations,8,RIP 路由的 Metrics,RIP 使用跳數(shù)作為路由的metric值 使用一個(gè)鄰居的接口就是1跳 RIP路由進(jìn)程會(huì)從多條等值路由中任意選一條，加入路由表,TR,10.0,5.1,5.2,5.3,5.4,C 4.0 dir conn Ser0,C 5.0 dir conn Eth0,R 10.0 120/4 via 5.2, Eth0,R 10.0 120/4 via 5.3, Eth0,R 10.0 120/4 via 5.4, Eth0,4.0,FDDI,2019/7/11,Yang Wu-Jun,xian Institute of Post and Telecommuniations,9,路由器轉(zhuǎn)發(fā)分組,路由協(xié)議維持和鄰接路由器的鄰居關(guān)系 鄰居路由器之間通過路由協(xié)議交換以下分組: Hello分組 路由更新分組 路由表中包含從鄰居路由器學(xué)來的路由 路由器通過將分組轉(zhuǎn)發(fā)到下一跳設(shè)備的方式來將分組最終傳遞到目的網(wǎng)絡(luò)。,2019/7/11,Yang Wu-Jun,xian Institute of Post and Telecommuniations,10,Map Table (WAN),基本轉(zhuǎn)發(fā)功能,幀校驗(yàn)和 分組緩存,將 目的IP地址與下一跳設(shè)備， 以及出端口關(guān)聯(lián)起來,將下一跳IP地址與下一跳關(guān)聯(lián) 起來,成幀、轉(zhuǎn)發(fā)分組,Inbound Interface,Routing Table,ARP Cache (LAN),Outbound Interface,由路由協(xié)議維護(hù)*,由 ARP 或 Inverse ARP 進(jìn)程維護(hù)s*,1,2,3,4,* 可以手工維護(hù)、創(chuàng)建,2019/7/11,Yang Wu-Jun,xian Institute of Post and Telecommuniations,11,分類路由協(xié)議概述,分類路由是距離矢量型協(xié)議進(jìn)行路由計(jì)算的結(jié)果 RIPv1 IGRP 掩碼不隨周期型發(fā)送的路由更新消息傳送 在網(wǎng)絡(luò)內(nèi), 每一類地址的掩碼默認(rèn)是固定的。,2019/7/11,Yang Wu-Jun,xian Institute of Post and Telecommuniations,12,分類路由,子網(wǎng)路由被同一個(gè)網(wǎng)絡(luò)內(nèi)的設(shè)備共享 匯總后的路由在外部網(wǎng)絡(luò)之間交換 匯總路由會(huì)在A，B，或C類網(wǎng)絡(luò)的邊界自動(dòng)創(chuàng)建。,,,, , , ,,2019/7/11,Yang Wu-Jun,xian Institute of Post and Telecommuniations,13,分類路由的子網(wǎng)需求,網(wǎng)絡(luò)中所有的路由器接口要求有相同的子網(wǎng)掩碼。 缺點(diǎn)是地址的使用效率仍然不夠充分。,29 /27,8 /27,3 /27,5 /27,7 /27,S1,S0,E1,E0,E0,僅需要兩個(gè)主機(jī)地址，實(shí)際卻分配30個(gè)主機(jī)地址,2019/7/11,Yang Wu-Jun,xian Institute of Post and Telecommuniations,14,無分類路由簡(jiǎn)介,無分類路由協(xié)議路由掩碼隨路由更新消息一起傳播 t OSPF EIGRP RIPv2 IS-IS BGP 在一個(gè)網(wǎng)絡(luò)內(nèi)部是否匯總路由可以手動(dòng)控制,2019/7/11,Yang Wu-Jun,xian Institute of Post and Telecommuniations,15,無類型子網(wǎng)的需求,同一個(gè)網(wǎng)絡(luò)內(nèi)的路由器接口可以有不同的子網(wǎng)掩碼 Variable-length subnet masking (VLSM)支持 該方式最大限度地提高了IP地址的利用率,29 /27,09 /30,3 /27,5 /27,10 /30,S1,S0,E1,E0,E0,僅需要兩個(gè)主機(jī)地址 VLSM 支持該要求,2019/7/11,Yang Wu-Jun,xian Institute of Post and Telecommuniations,16,距離向量路由更新,在距離向量協(xié)議中, 路由更新消息只在直接相連的鄰居路由器之間傳播。,Routing Table,所有路由,2019/7/11,Yang Wu-Jun,xian Institute of Post and Telecommuniations,17,距離向量路由協(xié)議,路由協(xié)議依靠IP分組傳遞路由信息,UDP Header,Port No.,Segment Payload,IP Header,Protocol Number,Frame Header,C R C,Packet Payload,Frame Payload,9 - IGRP 6 - TCP 17 - UDP,520 - RIP 69 - TFTP 53 - DNS,2019/7/11,Yang Wu-Jun,xian Institute of Post and Telecommuniations,18,距離向量協(xié)議比較,Characteristic RIPv1 RIPv2 IGRP EIGRP Count to infinity X X X Split horizon X X X X Hold-down timer X X X Triggered updates with route poisoning X X X X Load balancingEqual paths X X X X Load balancingUnequal paths X X VLSM support X X Routing algorithm B-F B-F B-F DUAL Metric Hops Hops Comp Comp Hop count limit 16 16 100 100 Scalability Med Med Large Large,*,2019/7/11,Yang Wu-Jun,xian Institute of Post and Telecommuniations,19,鏈路狀態(tài)路由更新,在鏈路狀態(tài)協(xié)議中, 鏈路狀態(tài)通告在整個(gè)路由域中的所有設(shè)備間傳遞。 通過分層設(shè)計(jì)來限制一條更新通告要傳遞給所有設(shè)備的情況,Routing Table,一條路由,2019/7/11,Yang Wu-Jun,xian Institute of Post and Telecommuniations,20,鏈路狀態(tài)協(xié)議比較,Characteristic OSPF IS-IS EIGRP Hierarchical topologyRequired X X Retains knowledge of all possible routes X X X Route summarizationManual X X X Route summarizationAutomatic X Event-triggered announcements X X X Load balancingEqual paths X X X Load balancingUnequal paths X VLSM support X X X Routing algorithm Dijkstra IS-IS DUAL Metric Cost Cost Comp Hop count limit 200 1024 100 Scalability Large VryLg Large,*,*,2019/7/11,Yang Wu-Jun,xian Institute of Post and Telecommuniations,21,Convergence,匯聚時(shí)間指：網(wǎng)絡(luò)發(fā)生一次變化后， 所有路由器對(duì)網(wǎng)絡(luò)拓?fù)渲匦逻_(dá)成一致所需要的時(shí)間: 增加新路由 現(xiàn)有路由狀態(tài)改變 影響匯聚時(shí)間的因素: 更新機(jī)制 (hold-down timers) 路由表的大小 路由算法 媒介類型,2019/7/11,Yang Wu-Jun,xian Institute of Post and Telecommuniations,22,RIP Convergence,步驟: 1. C 檢測(cè)到鏈路故障; 發(fā)送更新給 D 和 B - 到 B和D的路由被中毒; 從C的路由表中刪除 2. C 給鄰居發(fā)送消息請(qǐng)求替換路由 - v1使用廣播, v2使用多播 3. D 報(bào)告沒有替換路由; B 報(bào)告有一條替換路由 - 通過B的路由立即加入路由表中 4. C 將經(jīng)B的路由周期廣播給D - 但D由于處于 hold-down時(shí)間內(nèi)，不會(huì)改變路由表 5. 在 D, E,和F中, 由于 hold-down 定時(shí)器期滿, 新路由被加進(jìn)路由表 - 新路由按周期更新方式傳播 F的匯聚時(shí)間: hold-down 時(shí)間兩到三個(gè)更新時(shí)間,S1,S0,E1,E0,S0,S0,E0,F,E,B,A,C,D,2019/7/11,Yang Wu-Jun,xian Institute of Post and Telecommuniations,23,OSPF Convergence,S1,S0,E1,E0,S0,S0,E0,步驟: 1. C 檢測(cè)到鏈路故障; 發(fā)送鏈路狀態(tài)廣播給 D和B - Topology change is detected, traffic forwarding suspended 2. 所有路由器更新 網(wǎng)絡(luò)拓?fù)鋽?shù)據(jù)庫(kù);并向鄰居洪泛LSA - All devices have topological awareness 3. 所有路由器執(zhí)行 Dijkstra算法, 生成新的路由表 - Route via B in routing tables, traffic forwarding resumed F的匯聚時(shí)間: 大約6秒,F,E,B,A,C,D,2019/7/11,Yang Wu-Jun,xian Institute of Post and Telecommuniations,24,Single Entry,路由更新,Routing Table,Routing Table,整張 路由表,Distance Vector,方法,Link-State,方法,路由信息的發(fā)送方式,分類和無分類的路由更新,/24,/24,,RIPv1 網(wǎng)絡(luò),A,B,分類和無分類的路由更新,/24,C,,Routing table /16,/24,,RIPv1 網(wǎng)絡(luò),A,B,/24,分類和無分類的路由更新,/24,/24,/24,/24,OSPF 網(wǎng)絡(luò),A,B,/24,C,,Routing table /16,/24,,RIPv1 網(wǎng)絡(luò),A,B,分類和無分類的路由更新,/24,A,B,C,/24,Routing Table /24 /24,/24,/24,/24,/24,OSPF Network,A,B,/24,/24,C,,Routing Table /16,/24,,RIPv1 Network,A,B,2019/7/11,Yang Wu-Jun,xian Institute of Post and Telecommuniations,29,路由表,Entries are listed in an efficient search order Simplifies the search mechanism Multiple paths to a common destination can be listed Load balancing is enabled by default for IP Displayed by the show ip route command Entries can be refreshed by the clear ip route command Specify a single entry, u