基礎網路管理 第六章 路由與路由協定 製作：林錦財.

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1 基礎網路管理 第六章 路由與路由協定 製作：林錦財

2 大綱 遶送方式(路由表、位址解析) 靜態路由 路由協定分類 內部閘道協定與外部閘道協定 距離向量路由法與鏈結狀態路由法 路由協定的基本特性

3 什麼是路由 要實現路由路由器必須知道: 目的位址 來源位址 所有可能的路由路徑 最佳路由路徑 管理路由資訊 10.120.2.0
要實現路由路由器必須知道: 目的位址 來源位址 所有可能的路由路徑 最佳路由路徑 管理路由資訊

4 什麼是路由 路由器必須知道未和其直接相連的目的位址 路徑與轉送方向之決定 可路由協定: IP 10.120.2.0 172.16.1.0
E0 S0 Network Protocol Destination Network Exit Interface Connected Learned E0 S0 可路由協定: IP 路由器必須知道未和其直接相連的目的位址 路徑與轉送方向之決定

5 「靜態路由」與「動態路由」 靜態路由 動態路由 由網路管理員在路由器上手工添加路由資訊以實現路由目的
根據網路結構或流量的變化，路由協定會自動調整路由資訊以實現路由

6 靜態路由 在小型網路中適宜設置靜態路由。 有時靜態路徑用做備份之目的，亦即當動態路 徑失效時才被使用。 末節網路
(Stub Network) S0 網路 A B B 在小型網路中適宜設置靜態路由。 有時靜態路徑用做備份之目的，亦即當動態路 徑失效時才被使用。

7 配置靜態路由：ip route 命令 指定一條可以到達目標網路的路徑 管理性距離：0~255
RA(config)#ip route 目標網路 [子網遮罩] {下一跳位址 | 介面} [管理性距離] [permanent] 管理性距離：0~255 出口介面：管理性距離預設為 0 下一跳位址：管理性距離預設為 1

8 靜態路由的例子 末節網路 (Stub Network) 這是一條單方向的路徑， 必須配置一條相反的路徑。 命令 目標網路 子網遮罩
S0 網路 A B B 這是一條單方向的路徑， 必須配置一條相反的路徑。 Purpose: This figure gives an example of a static route configuration. ip route 命令 目標網路 子網遮罩 下一跳位址

9 靜態路由的例子 末節網路 (Stub Network) 這是一條單方向的路徑， 必須配置一條相反的路徑。 命令 目標網路 子網遮罩 出口介面
S0 網路 A B B 這是一條單方向的路徑， 必須配置一條相反的路徑。 Purpose: This figure gives an example of a static route configuration. ip route S0 命令 目標網路 子網遮罩 出口介面

10 預設路由 使用預設路由後，Stub Network可以到達路由器A以外的網路。 Stub Network Network
SO Network A B B Purpose: This figure gives an example of a default route configuration. Emphasize: With an address and subnet mask of in the ip route statement, packets for any network not listed in the routing table will be sent to the next hop, ip route 使用預設路由後，Stub Network可以到達路由器A以外的網路。

11 查看路由表 RouterA# sh ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B – BGP, D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area, N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2, E1 - OSPF external type 1, E2 - OSPF external type 2, E – EGP, i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia – IS-IS inter area, * - candidate default, U - per-user static route, o – ODR, P – periodic downloaded static route, T - traffic engineered route Gateway of last resort is not set C is directly connected, Serial0/0 S [1/0] via C /24 is directly connected, FastEthernet0/0

12 動態路由 動態路由是使用協定來尋找網路，並更新路由 器上的路徑表 路由器之間互相交換路由資訊
比使用靜態路由或預設路由容易，但會消耗路由 器的CPU處理能力與網路線路的頻寬 路由器之間互相交換路由資訊 定期交換 有變動時交換

13 可路由協定: IP 路由協定: RIP, IGRP, OSPF, EIGRP
路由協定：用於路由器選擇路徑和管理路由表。 一旦選擇了一條路徑後，路由器將路由可路由協定 。 E0 S0 Network Protocol Destination Network Exit Interface Connected RIP IGRP E0 S0 S1 可路由協定: IP 路由協定: RIP, IGRP, OSPF, EIGRP

14 「可路由協定」與「路由協定」 可路由協定( Routed Protocol)：用以導送用戶 交通。提供資料包足夠的網路層位址資訊，以 允許資料包根據定址方案由一台主機轉送到另 一台主機。例如：IP；IPX；AppleTalk 路由協定 （Routing Protocol)：用以建立和維 護路由表。使路由器間可以互相分享有關網路 與其鄰近的資訊。例如：RIP；IGRP； EIGRP；OSPF；BGP；IS-IS 等

15 自治系統：內部和外部的 路由協定 自治系統 200 自治系統 100 IGPs: RIP, IGRP, OSPF, EIGRP
EGPs: BGP 自治系統 100 自治系統 200 Purpose: This figure discusses autonomous systems, IGPs. and EGPs. Emphasize: Introduce the interior/exterior distinctions for routing protocols: Interior routing protocols are used within a single autonomous system Exterior routing protocols are used to communicate between autonomous systems. The design criteria for an interior routing protocol require it to find the best path through the network. In other words, the metric and how that metric is used is the most important element in an interior routing protocol. Exterior protocols are used to exchange routing information between networks that do not share a common administration. IP exterior gateway protocols require the following three sets of information before routing can begin: A list of neighbor (or peer) routers or access servers with which to exchange routing information A list of networks to advertise as directly reachable The autonomous system number of the local router 自治系統：使用相同的路由準則管理下的網路集合 (16 bit 編號) 內部閘道協定(Interior Gateway Protocol, IGP)在一個自治系統內 運行。 外部閘道協定(Exterior Gateway Protocl, EGP)連接不同的自治系 統。

16 內部與外部路由協定 內部閘道協定(Interior Gateway Protocol, IGP)
是在同一自治系統(Autonomous System, AS)中的路由器用來交換資訊的協定 如RIP, IGRP, EIGRP, OSPF, IS-IS 外部閘道協定(Exterior Gateway Protocol, EGP) 使用在AS之間 如EGP, BGP

17 路由協定的分類 距離向量 B C A D 混合路由 B 鏈路狀態 C A D

18 路由的不可信度 我需要送封包至網路 E，路由器 B 與 C 都可以到達。哪個路由最佳? E IGRP Administrative
Distance=100 Router B Router A RIP Administrative Distance=120 E Router C Router D

19 常用度量和metric值 Hop ; bandwidth ;delay ; load ; reliability; ticks ; cost

20 收斂時間 收斂時間 （convergence time):從網路拓撲發 生變化到網路中所有路由器都知道這個表化的 時間就叫 收斂時間

21 Distance—How far Vector—In which direction
距離向量的路由協定 B C A Distance—How far Vector—In which direction D D C B A Routing Table Routing Table Routing Table Routing Table 定期將路由表複製給相鄰的路由器並且進行向量堆加 Bellman-Ford 演算法

22 距離向量—源資訊的獲得 路由器從收集到的來源資訊中選擇到達目標位 址的最佳路徑 10.1.0.0 10.2.0.0 10.3.0.0 A B
E0 A S0 B C S0 S1 S0 E0 Routing Table Routing Table Routing Table E0 S0 S0 S1 S0 E0 路由器從收集到的來源資訊中選擇到達目標位 址的最佳路徑

23 距離向量—選擇最佳路徑 用於確定最佳路由路徑的參數資訊 A IGRP Bandwidth Delay Load Reliability
MTU 56 RIP Hop count T1 56 IPX Ticks, hop count T1 B 用於確定最佳路由路徑的參數資訊

24 距離向量—管理路由資訊 路由表的更新過程將通過路由器之間一步一步來完成 A 更新路由表 網絡結構的 改變將導致 路由表的 更新
Layer 1 of 3: Purpose: This figure continues the concept of how a router using a distance vector protocol generally performs its routing information update process when the network topology changes. Emphasize: This layer shows the bullet point, the router on the right, and, on the right, a topology change; routing tables will need updating to reflect this topology change. A 路由表的更新過程將通過路由器之間一步一步來完成

25 路由表的更新過程將通過路由器之間一步一步來完成
距離向量—管理路由資訊 更新路由表 在下一個週期後 路由器A發送更新 過的路由表 網絡結構的 改變將導致 路由表的 更新 Layer 2 of 3: Emphasize: Layer 2 adds the updated routing table that router A sends out after it processes the topology change. A 路由表的更新過程將通過路由器之間一步一步來完成

26 路由表的更新過程將通過路由器之間一步一步來完成
距離向量—管理路由資訊 更新路由表 更新路由表 在下一個週期後 路由器A發送更新 過的路由表 網絡結構的 改變將導致 路由表的 更新 Layer 3 of 3: Layer 3 adds router B, which receives the updated routing table from router?A. In turn, router B will perform its own process to update its routing table given this new topology update from router A. Distance vector updates occur step by step. Typically, a router sends updates by multicasting its table on each configured port, but other methods, such as sending the table only to preconfigured neighbors, are employed by some routing algorithms. Multicast is used by the RIP2, OSPF, and EIGRP routing protocols. RIP and IGRP use broadcast. The routing table can be sent routinely and periodically, or whenever a change in the topology is discovered. Updates sent when changes occur are called triggered updates. B A 路由表的更新過程將通過路由器之間一步一步來完成

27 路由迴路 每一個節點管理著與之相連的所有網路 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0 A B C E0 S0
Routing Table Routing Table Routing Table E0 S0 S0 S0 S1 E0 Slide 1 of 4: Prupose: This figure describes the first of the general problems that a distance vector protocol could face without the corrective influence of some countermeasure. Emphasize: Layer 1 shows the original state of the network and routing tables. All routers have consistent knowledge and correct routing tables. In this example, the cost function is hop count so the cost of each link is 1. Router C is directly connected t??? S0 1 S1 1 S0 1 S0 2 S0 1 S0 2 每一個節點管理著與之相連的所有網路

28 X 路由迴路 緩慢的收斂容易造成路由資訊的不一致 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0 A B C E0
S0 B C S0 S1 S0 E0 Routing Table Routing Table Routing Table E0 S0 S0 S0 S1 E0 Down Slide 2 of 4: Emphasize: In Layer 2, router C has detected the failure of network and stops routing packets out its E0 interface. However, router A has not yet received notification of the failure and still believes it can access network through router??? S0 1 S1 1 S0 1 S0 2 S0 1 S0 2 緩慢的收斂容易造成路由資訊的不一致

29 X 路由迴路 路由器C 推斷到達10.4.0.0 網路的最好路徑是通過路由器B 10.1.0.0 10.2.0.0 10.3.0.0
E0 A S0 B C S0 S1 S0 E0 Routing Table S0 1 2 E0 S1 Slide 3 of 4: Emphasize: Because router B’s routing table indicates a path to network , router C believes it now has a viable path to through router B. Router C updates its routing table to reflect a path to network with a hop count of 2. 路由器C 推斷到達 網路的最好路徑是通過路由器B

30 X 路由迴路 路由器 A 根據錯誤的資訊升級它的路由表 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0 A B C
E0 A S0 B C S0 S1 S0 E0 Routing Table Routing Table Routing Table E0 S0 S0 S1 S0 2 Slide 4 of 4: Emphasize: In Layer 4, router A receives the new routing table from router B, detects the modified distance vector to network , and recalculates its own distance vector to network as 3. If all routers in an internetwork do not have up-to-date, accurate information about the state of the internetwork, they might use incorrect routing information to make a routing decision. The use of incorrect information might cause packets to take less-than-optimum paths or paths that return packets to routers that they have already visited. 1 3 1 2 1 2 路由器 A 根據錯誤的資訊升級它的路由表

31 X 路由迴路 路由器 A 根據錯誤的資訊升級它的路由表 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0 A B C
E0 A S0 B C S0 S1 S0 E0 Routing Table Routing Table Routing Table E0 S0 S0 S1 S0 2 Slide 4 of 4: Emphasize: In Layer 4, router A receives the new routing table from router B, detects the modified distance vector to network , and recalculates its own distance vector to network as 3. If all routers in an internetwork do not have up-to-date, accurate information about the state of the internetwork, they might use incorrect routing information to make a routing decision. The use of incorrect information might cause packets to take less-than-optimum paths or paths that return packets to routers that they have already visited. 1 3 1 4 1 2 路由器 A 根據錯誤的資訊升級它的路由表

32 X 路由迴路 路由器 A 根據錯誤的資訊升級它的路由表 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0 A B C
E0 A S0 B C S0 S1 S0 E0 Routing Table Routing Table Routing Table E0 S0 S0 S1 S0 4 Slide 4 of 4: Emphasize: In Layer 4, router A receives the new routing table from router B, detects the modified distance vector to network , and recalculates its own distance vector to network as 3. If all routers in an internetwork do not have up-to-date, accurate information about the state of the internetwork, they might use incorrect routing information to make a routing decision. The use of incorrect information might cause packets to take less-than-optimum paths or paths that return packets to routers that they have already visited. 1 3 1 4 1 2 路由器 A 根據錯誤的資訊升級它的路由表

33 X 無限計數 10.4.0.0 網路的資料將在路由器 A, B, 和 C 之間迴圈 10.4.0.0 網路的跳數將無限大 10.1.0.0
X E0 A S0 B C S0 S1 S0 E0 Routing Table Routing Table Routing Table E0 S0 S0 S1 S0 4 Purpose: This figure describes another of the general problems that a distance vector protocol could face without the corrective influence of some countermeasure. Emphasize: Both routers conclude that the best path to network is through each other and continue to bounce packets destined for network between each other, incrementing the distance vector by 1 each time. This condition, called count-to-infinity, continuously loops packets around the network, despite the fundamental fact that the destination network is down. While the routers are counting to infinity, the invalid information allows a routing loop t???! 1 5 1 6 1 2 網路的資料將在路由器 A, B, 和 C 之間迴圈 網路的跳數將無限大

34 X 解決方法：定義最大跳數 指定最大跳數來防止路由回環 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0 A B C
E0 A S0 B C S0 S1 S0 E0 Routing Table S0 1 2 16 E0 S1 Purpose: This figure describes a corrective measure that attempts to solve the routing loop problems that a distance vector protocol could face. Emphasize: Routing loops occur only when routing knowledge being propagated has not yet reached the entire internetwork—when the internetwork has not converged after a change. Fast convergence minimizes the chance for a routing loop to occur, but even the ???!To avoid prolonging the count-to-infinity time span, distance vector protocols define infinity as some maximum number. This number refers to a routing metric, such as a hop count. With this approach, the routing protocol permits the routing loop until the metric exceeds its maximum allowed value. This example shows this defined maximum as 16 hops. Once the metric value exceeds the maximum, network is considered unreachable.??? 指定最大跳數來防止路由回環

35 X X X 解決方法：水平分割 不會接收到由自身傳達出去的路由資訊 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0
E0 A S0 B C S0 S1 S0 E0 X X Routing Table S0 1 2 E0 S1 E1 Purpose: This figure introduces the corrective measure known as “split horizon.” The split horizon technique attempts to solve routing loops. Emphaisze: The split horizon technique attempts to eliminate routing loops and speed up convergence. The rule of split horizon is that it is never useful to send information about a route back in the direction from which the original packet came. In the ex???Router C originally announced a route to network to router B. It makes no sense for router B to announce to router C that router B has access to network through router C. Given that router B passed the announcement of its route to network to router A, it makes no sense for router A to announce its distance from network to router B. Because router B has no alternative path to network , router B concludes that network is inaccessible. In its basic form, the split horizon technique simply omits from the message any information about destinations routed on the link. This strategy relies either on routes never being announced or on old announcements fading away through a timeout mechanism.???Split horizon also improves performance by eliminating unnecessary routing updates. Under normal circumstances, sending routing information back to the source of the information is unnecessary. 不會接收到由自身傳達出去的路由資訊

36 X 解決方法：路由毒殺 路由器將該路由資訊的跳數標記為無限大 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0 A B
E0 A S0 B C S0 S1 S0 E0 Routing Table S0 1 2 Infinity E0 S1 E1 Purpose: This figure expands on the split horizon technique by adding the concept of poisonous reverse updates. Emphasize: Route poisoning closes the potential for longer routing loops. Fast convergence minimizes the chance for a routing loop to occur, but even the smallest interval leaves the possibility open. With a poison route in place, router B can maintain a s??? 路由器將該路由資訊的跳數標記為無限大

37 X 解決方法：反向毒殺 反向毒殺(Poison Reverse)可以超越水平分割 10.1.0.0 10.2.0.0 10.3.0.0
X E0 A S0 B C S0 S1 S0 E0 Poison Reverse Routing Table S0 1 2 Infinity E0 S1 E1 Possibly Down Purpose: This figure explains poison reverse.. Emphasize: Poison reverse overrides the split horizon solution. 反向毒殺(Poison Reverse)可以超越水平分割

38 解決方法：Hold-Down 計時 網路 是無法到達的 Update after hold-down Time X E0 A S0 B C S0 S1 S0 E0 Update after hold-down Time Purpose: This figure describes how hold-down timers avoid the general problems that a routing protocol could face. Emphasize: Hold-down timers are used to prevent regular update messages from inappropriately reinstating a route that may have gone bad. Hold-downs tell routers to hold any changes that might affect routes for some period of time. The hold-down period is usually calculated to be just greater than the period of time necessary to update the entire network with a routing change. Note: A network administrator can configure the hold-down timers on several routers to work together in tandem. 網路 是 down 接著回復 up 再接著又 down 路由器在Hold-Down時間內將該條記錄標記為「可能down」 (possibly down)以使其他路由器能夠重新計算網路結構的變化

39 X 解決方法：觸發更新 當路由表發生變化時路由器立即發送更新資訊 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0 A
網路 是無法到達的 網路 是無法到達的 網路 是無法到達的 X E0 A S0 B C S0 S1 S0 E0 Purpose: This figure describes how triggered updates avoid the general problems that a routing protocol could face. Emphasize: Normally, new routing tables are sent to neighboring routers on a regular basis. A triggered update is a new routing table that is sent immediately, in response to some change. Each update triggers a routing table change in the adjacent routers, which, in turn, generate triggered updates notifying their adjacent neighbors of the change. This wave propagates throughout that portion of the network where routes went through the link???Triggered updates would be sufficent if we could guarantee that the wave of updates reached every appropriate router immediately. However, there are two problems: Packets containing the update message can be dropped or corrupted by some link in the network. The triggered updates do not happen instantaneously. It is possible that a router that has not yet received the triggered update will issue a regular update at just the wrong time, causing the bad route to be reinserted in a neighbor that had already recei???!Coupling triggered updates with holddowns is designed to get around these problems. Because the hold-down rule says that when a route is removed, no new route will be accepted for the same destination for some period of time, the triggered update has time to propagate throughout the network. 當路由表發生變化時路由器立即發送更新資訊

40 迴路解決方法組合應用 觸發更新(Triggered Update) Hold-Down 計時器 反向毒殺 (Poison Reverse)
水平分割 (Split Horizontal)

41 一個完整的方案 X 觸發更新 觸發更新 10.4.0.0 D E B A C Slide 1 of 6:
Purpose: This page begins a series of graphics that tie all the solutions together by showing how each solution works to prevent routing loops in a more complex network design. Emphasize: Begin this series by describing that router B poisons its route to network 觸發更新 A

42 一個完整的方案 X 10.4.0.0 D E B A C Holddown Holddown Holddown Slide 2 of 6:
Purpose: This figure continues to describe how the solution works to prevent routing loops in a more complex network design. Emphasize: Describe that routers D and A both set their holddown timers and send triggered updates to router E about the status of network E also sets its holddown timer. Holddown A Holddown

43 一個完整的方案 X 10.4.0.0 D E B A C Holddown Poison Reverse Poison Reverse
Slide 3 of 6: Purpose: This figure continues to describe how the solution works to prevent routing loops in a more complex network design. Emphasize: A and D send a poison reverse to B. E sends a poison reverse to B. Holddown Poison Reverse Poison Reverse A Holddown

44 一個完整的方案 X 10.4.0.0 D E B A C Holddown Holddown 目標為網路 10.4.0.0的封包 目標為網路
Slide 4 of 6: Purpose: This figure continues to describe how the solution works to prevent routing loops in a more complex network design. Emphasize: While in holddown state router A, D, and E will still attempt to forward packets to network Holddown 目標為網路 的封包 目標為網路 的封包 A Holddown

45 一個完整的方案 Link up! 觸發更新 觸發更新 10.4.0.0 D E B A C Slide 5 of 6:
Purpose: This figure continues to describe how the solution works to prevent routing loops in a more complex network design. Emphasize: When the link is back up, B will send a triggered update to A and D notifying them that network is active. 觸發更新 A

46 一個完整的方案 Link up! 觸發更新 觸發更新 10.4.0.0 D E B A C Slide 6 of 6:
This graphic continues to describe how the solution works to prevent routing loops in a more complex network design. A and D, inturn, update E that network is now up. 觸發更新 A

47 鏈路狀態協定原理 1：路由器找到自己鄰居 2：每個路由器向鄰居發送「鏈路狀態通告」(LSA, link state advertisement) 資料包，包含了自己的鏈路成本 3：LSA 擴散，每個路由器都得到相同拓撲結構的資料庫 4：由 Dijkstra‘s SPF演算法計算網路可達性，建立SPF樹，以自己為樹根 5：建立路由表，列出最優路徑列表；維護其他拓撲結構和狀態細節資料庫。

48 LSA（link state advertisement)數據包
鏈路狀態協定 B C A D LSA（link state advertisement)數據包 鏈路狀態公告 拓樸結構資料 Purpose: This figure introduces the link-state routing algorithm, the second of the classes of routing protocols, and outlines how it operates. Emphasize: In contrast with the analogy about the distance vector information being like individual road signs that show distance, link-state information is somewhat analogous to a road map with a “you are here” pointer showing the map reader’s current loc???Link-state routing is not covered further in this course. Refer students interested in more details to the ACRC course. 路由表 SPF 運算 最佳路由資訊 傳遞最佳的路徑資訊給其他的路由器

49 鏈路狀態協定特點 需要最多的處理能力與記憶體 頻寬之消耗主要在初始鏈路狀態的LSA泛洪時

50 Converge rapidly using
混合路由 選擇基於距離向量的路徑 Converge rapidly using 通過傳遞變化的更新資訊 達到快速收斂 平衡的路由 Purpose: This figure introduces and describes a third routing protocol class, the balanced hybrid. Emphasize: Indicate how balance hybird protocols such as Enhanced IGRP operate with elements of both distance vector and link-state routing protocols. The EIGRP balanced hybrid routing protocol is covered in the ACRC course, not in this course. 距離向量和環狀路由的綜合應用 例如：EIGRP

51 IP路由的配置任務 路由器配置 全域配置 介面配置 選擇路由協定 指定網路 驗證介面位址與子網遮罩 Network 172.16.0.0
RIP IGRP, RIP IGRP Network RIP Network

52 動態路由配置 Router(config)#router 協定 [關鍵字]
協定：指定IP路由協定 關鍵字選項 IGRP與EIGRP需要自治系統編號； OSPF需要行程編號； RIP 不需要 Router(config-router)#network network-number 指定與路由器直接相連的網路

53 IP 路由協定 自治系統 200 自治系統 100 IGPs: RIP, IGRP, OSPF, EIGRP EGPs: BGP
IGRP – Cisco 距離向量內部路由協定 OSPF – 鏈結狀態內部路由協定 EIGRP – 進階 Cisco 距離向量內部路由協定 BGP – 距離向量外部路由協定

54 RIP RIP 最初規格書為 RFC 1058 ，其主要特點包 括： 距離向量路由協定 用躍數為路徑選擇之量度 若躍數大於 15，封包被丟棄
路由更新預設每 30 廣播

55 IGRP IGRP 為 Cisco 發展的專屬協定，其主要設計 特性為： 距離向量路由協定
使用Bandwidth, load, delay and reliability 以建立 複合的量度 路由更新預設每 90 廣播.

56 OSPF OSPF 不是專屬的鏈路狀態路由協定，是在 RFC 2328公開的路由協定標準
路由更新是當發生拓樸改變時被泛洪

57 EIGRP EIGRP 是 Cisco 專屬的加強距離向量路由協 定，其主要特點為：
使用非等成本負載平衡 (unequal cost load balancing) 使用距離向量與鏈結狀態特徵之組合 使用擴散更新演算法 (Diffusing Update Algorithm, DUAL) 以計算最短路徑 路由更新是由拓樸改變所激發，並使用 群播

58 BGP Border Gateway Protocol (BGP) 是外部路由 協定，主要特性為： 為距離向量外部路由協定
用於 ISP 之間或是 ISP 與客戶之間 用於在自治系統之間繞送 Internet 交通

59 總結 靜態路由的目的 自治系統 內部與外部路由協定 距離向量法與鏈結狀態法 動態路由協定之配置