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RouterC E0 ）和 Net 1 中斷時，GW 2 (Router A s0) 經由 GW 1 到達 Net 1 時，距離為 2，一旦中斷，GW 2 不會再對 GW 1 廣播這條路徑，GW 1 也停止廣播此網路至 Net 1 的路徑，經過幾回合路徑更新後，各個閘道會發現此網路 Net 1 是 unreachabel，便不會造成迴圈了。\n \n 路由器 A 和 路由器 B 的 192.168.4.0 這網段是由路由器 C 所學習來的，所以不會反向更新路徑。\n \n \n \n Router A \n \n GW2\n s0 s1\n / \\\n 192.168.1.0 / \\ 192.168.3.0\n / \\\n / \\\n s1 s0 ----- s1 s0 \n \n 192.168.2.0\n GW1\n Router B Router C E0 ---X--- E0 Router D\n \n 192.168.4.0\n \n \n +--------------------------+ \n | Routing Table A |\n +--------------------------+\n | IP | Int | Metric | \n +-----------+-----+--------+\n |192.168.1.0| s0 | 0 |\n +-----------+-----+--------+\n |192.168.3.0| s1 | 0 |\n +-----------+-----+--------+\n |192.168.2.0| s0 | 1 |\n +-----------+-----+--------+\n |192.168.4.0| s0 | 2 |\n +-----------+-----+--------+\n \n \n +--------------------------+ \n | Routing Table B |\n +--------------------------+\n | IP | Int | Metric | \n +-----------+-----+--------+\n |192.168.1.0| s1 | 0 |\n +-----------+-----+--------+\n |192.168.2.0| s0 | 0 |\n +-----------+-----+--------+\n |192.168.3.0| s0 | 1 |\n +-----------+-----+--------+\n |192.168.4.0| E0 | 1 |\n +-----------+-----+--------+\n \n \n +--------------------------+ \n | Routing Table C |\n +--------------------------+\n | IP | Int | Metric | \n +-----------+-----+--------+\n |192.168.2.0| s1 | 0 |\n +-----------+-----+--------+\n |192.168.3.0| s0 | 0 |\n +-----------+-----+--------+\n |192.168.1.0| s1 | 1 |\n +-----------+-----+--------+\n |192.168.4.0| E0 | down |\n +-----------+-----+--------+\n \n \n +--------------------------+ \n | Routing Table D |\n +--------------------------+\n | IP | Int | Metric | \n +-----------+-----+--------+\n |192.168.4.0| E0 | 0/down |\n +-----------+-----+--------+\n \n \n# 觸發更新 \n \n* Poison Reverse + * Triggered Updates, 毒性逆向 ＋ 觸發更新\n\n(移除不正確資訊)\n\n此法規定原本最先廣播該路徑的 GW 遇到路徑中斷時，必須將路徑修改至無限長 (= 16)，此資訊亦將保留若干週期。觸發更新則是當閘道器收到故障通知時，會立刻廣播，不會等到下一個路徑更新時方才廣播。\n\n實際觀察路由表變化，來知曉 Poison Reverse 的運作機制，倘若 路由器 C 介面 E0 線路中斷， metric 值會變成 infinite，路由器 B 會送 Poison Reverse 給路由器 C ，告知此網段無法存取 unaccessable。\n\n \n \n \n +--------------------------+ \n | Routing Table B |\n +--------------------------+\n | IP | Int | Metric | \n +-----------+-----+--------+\n |192.168.1.0| s1 | 0 |\n +-----------+-----+--------+\n |192.168.2.0| s0 | 0 |\n +-----------+-----+--------+\n |192.168.3.0| s0 | 1 |\n +-----------+-----+--------+\n |192.168.4.0| E0 |infinite|\n +-----------+-----+--------+\n \n \n +--------------------------+ \n | Routing Table C |\n +--------------------------+\n | IP | Int | Metric | \n +-----------+-----+--------+\n |192.168.2.0| s1 | 0 |\n +-----------+-----+--------+\n |192.168.3.0| s0 | 0 |\n +-----------+-----+--------+\n |192.168.1.0| s1 | 1 |\n +-----------+-----+--------+\n |192.168.4.0| E0 |infinite|\n +-----------+-----+--------+\n \n\n# 延長時間\n \n* Hold Down Timer, 倒數計時更新法\n\n（防止迴路）\n\n此更新方式是用來解決故障資訊比正當資訊傳送的慢的問題，原理是讓故障資訊保持充足時間傳送，當閘道器收到此網路 unreachable 時，一定時間內，例如 60 秒內，閘道器不會再接收關於這網路的路徑資訊。\n\n缺點是，此法會造成迴圈，使得網路效率大減。\n\n可見實際路由表變化，來觀察 Hold Down Timer 的運作機制，當路由器 C 介面 E0 線路中斷後，介面 E0 的 metric 值改成 down，並且通知路由器 B，再通知路由器 A，AB 都在 Holddown 時間過後，方才更新路由表。\n\n\n \n Router A \n \n GW2\n s0 s1\n / \\\n 192.168.1.0 / \\ 192.168.3.0\n / \\\n / \\\n s1 s0 ----- s1 s0 \n \n 192.168.2.0\n GW1\n Router B Router C E0 ---X--- E0 Router D\n \n 192.168.4.0\n \n \n +--------------------------+ \n | Routing Table A |\n +--------------------------+\n | IP | Int | Metric | \n +-----------+-----+--------+\n |192.168.1.0| s0 | 0 |\n +-----------+-----+--------+\n |192.168.3.0| s1 | 0 |\n +-----------+-----+--------+\n |192.168.2.0| s0 | 1 |\n +-----------+-----+--------+\n |192.168.4.0| s0 | 2 |\n +-----------+-----+--------+\n \n \n +--------------------------+ \n | Routing Table B |\n +--------------------------+\n | IP | Int | Metric | \n +-----------+-----+--------+\n |192.168.1.0| s1 | 0 |\n +-----------+-----+--------+\n |192.168.2.0| s0 | 0 |\n +-----------+-----+--------+\n |192.168.3.0| s0 | 1 |\n +-----------+-----+--------+\n |192.168.4.0| E0 | 1 |\n +-----------+-----+--------+\n \n \n +--------------------------+ \n | Routing Table C |\n +--------------------------+\n | IP | Int | Metric | \n +-----------+-----+--------+\n |192.168.2.0| s1 | 0 |\n +-----------+-----+--------+\n |192.168.3.0| s0 | 0 |\n +-----------+-----+--------+\n |192.168.1.0| s1 | 1 |\n +-----------+-----+--------+\n |192.168.4.0| E0 | down |\n +-----------+-----+--------+\n \n \n +--------------------------+ \n | Routing Table D |\n +--------------------------+\n | IP | Int | Metric | \n +-----------+-----+--------+\n |192.168.4.0| E0 | 0/down |\n +-----------+-----+--------+\n \n\n\n# IGRP = Cisco RIP\n\n距離向量的，distance vector，然而與 RIP 不同之處在於：\n\n(1) 不受限於 15 個 hops，適用於大型互聯網路。\n\n(2) 提供 4 個路徑，藉以節省頻寬。\n\n(3) 每 90 秒廣播一次。\n\n(4) 不支援 VLSM。\n\n\n# IGRP 的參考用參數\n\n(影響 metric value/hops count)\n\n1. Bandwidth 頻寬\n\n2. Delay 時間\n\n3. Load 負載\n\n4. MTU 最大傳送單元（傳輸位元組）\n\n5. Reliability 可靠度、可信度（距離值越小越可靠）\n\n# 預設的距離值\n\n預設的距離值 （100、120）\n\nEIGRP \n\n +--------+---------------+\n | 路由方 | distance val |\n +--------+---------------+\n | int | 0 |\n +--------+---------------+\n | static | 1 |\n +--------+---------------+\n | EIGRP | 5 /90 |\n +--------+---------------+\n | BGP | 20 |\n +--------+---------------+\n | | |\n | IGRP | 100 |\n | | |\n +--------+---------------+\n | OSPF | 110 |\n +--------+---------------+\n | IS-IS | 115 |\n +--------+---------------+\n | RIP | 120 |\n +--------+---------------+\n | EGP | 140 |\n +--------+---------------+\n | ? | 255 |\n +--------+---------------+\n\n# RIP\n\n此為 Xerox 所開發的通訊協定，使用向量距離或是經過的閘道數 Hops Count 作為距離單位。此協定將閘道器分為主動的廣播和被動的收聽，同一時間下，一閘道器主動，則其餘閘道器皆為被動，以避免廣播風暴。\n\n向量距離不能保證最短的路徑最快，因為線路的材質也會影響速度，例如乙太網路線和其他慢速網路線的相互比較，而且路徑訊息可能在傳輸過程中發生錯誤，需要在每個收聽的閘道器上設有 timer 計時器，每當收到廣播閘道器的廣播資訊時，便開始倒數 180 秒 （3分鐘）若沒有收到同樣的路徑資訊，便視此路徑資訊無效。\n\n被動的閘道器不廣播，根據主動的閘道所廣播的路徑訊息調整自己的路由表（路徑表）。\n\n# Broadcast Storm\n\nhttps://zh.wikipedia.org/wiki/廣播風暴\n\n","project_url":"https://awesome.ecosyste.ms/api/v1/projects/github.com%2Fqueeniecplusplus%2Fccnp_igrp","html_url":"https://awesome.ecosyste.ms/projects/github.com%2Fqueeniecplusplus%2Fccnp_igrp","lists_url":"https://awesome.ecosyste.ms/api/v1/projects/github.com%2Fqueeniecplusplus%2Fccnp_igrp/lists"}