本次實驗探究DUAL，相關命令：debug eigrp fsm，show ip route， show ip eigrp topology， show ip eigrp topology all-links
相關鏈接：
EIGRP配置、分析、包——力求詳解（1）：http://425093014.blog.51cto.com/5109559/1060124
EIGRP配置、分析、包——力求詳解（2）：http://425093014.blog.51cto.com/5109559/1061059
友情提示：友情提示：如果圖片太小看不清楚，可以點擊圖片查看原圖，或者下載本次實驗資料。
如果你需要，可以到 http://down.51cto.com/data/602810 這裏去下載本次實驗的項目、代碼、配置保存文件，使用GNS3模擬。
拓撲圖：
簡介：
本次，將R1的接口s0/0關閉與啓用，來觀察DUAL的更新，使用debug eigrp fsm查看更新。
FD（Feasible Distance）：可行距離
RD（Reported Distance）：報告距離
FS（Feasible Successor）：可行後繼
FC（Feasible Condition）：可行條件
提示：關於DUAL的基礎理論可以查看CCNA的課本，本問不介紹理論，僅僅是爲理解而做，希望對你有用。
Router#sh ip route
Codes: C - connected, S - static, 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
i - IS-IS, su - IS-IS summary, 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
Gateway of last resort is not set
192.168.10.0/24 is variably subnetted, 3 subnets, 2 masks
D 192.168.10.0/24 is a summary, 00:01:24, Null0
C 192.168.10.4/30 is directly connected, Serial0/1
D 192.168.10.8/30 [90/2681856] via 192.168.10.6, 00:01:24, Serial0/1
172.16.0.0/16 is variably subnetted, 4 subnets, 3 masks
D 172.16.0.0/16 is a summary, 00:01:24, Null0
C 172.16.1.0/24 is directly connected, FastEthernet1/0
D 172.16.2.0/24 [90/2172416] via 172.16.3.2, 00:01:38, Serial0/0
C 172.16.3.0/30 is directly connected, Serial0/0
D 10.0.0.0/8 [90/2297856] via 172.16.3.2, 00:01:26, Serial0/0
D 192.168.1.0/24 [90/2172416] via 192.168.10.6, 00:01:26, Serial0/1
Router(config-if)#do show ip eigrp topology
IP-EIGRP Topology Table for AS(1)/ID(192.168.10.5)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
r - reply Status, s - sia Status
P 10.0.0.0/8, 1 successors, FD is 2297856
via 172.16.3.2 (2297856/128256), Serial0/0
P 192.168.10.0/24, 1 successors, FD is 2169856
via Summary (2169856/0), Null0
P 192.168.10.4/30, 1 successors, FD is 2169856
via Connected, Serial0/1
P 192.168.1.0/24, 1 successors, FD is 2172416
via 192.168.10.6 (2172416/28160), Serial0/1
P 192.168.10.8/30, 1 successors, FD is 2681856
via 192.168.10.6 (2681856/2169856), Serial0/1
P 172.16.0.0/16, 1 successors, FD is 28160
via Summary (28160/0), Null0
P 172.16.1.0/24, 1 successors, FD is 28160
via Connected, FastEthernet1/0
P 172.16.2.0/24, 1 successors, FD is 2172416
via 172.16.3.2 (2172416/28160), Serial0/0
P 172.16.3.0/30, 1 successors, FD is 2169856
via Connected, Serial0/0
Router#debug eigrp fsm
EIGRP FSM Events/Actions debugging is on
--開啓監控，將會收到更新內容
Router#conf t
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)#int s0/0
Router(config-if)#shutdown
Router(config-if)#
*Mar 1 00:06:00.415: DUAL: rcvupdate: 172.16.3.0/30 via Connected metric 4294967295/4294967295
--此句代表收到更新：度量變爲最大，代表172.16.3.0/30 不可達
*Mar 1 00:06:00.415: DUAL: Find FS for dest 172.16.3.0/30. FD is 2169856, RD is 2169856
--此句代表爲172.16.3.0/30 尋找可行後繼，在拓撲表中查找，show ip eigrp topology是查看該改路由器的拓撲表
--此處的FD即之前正常時的FD，可在上面的拓撲表中查看。
--只有當RD小於FD時，改路徑纔會變成FS。
*Mar 1 00:06:00.419: DUAL: 0.0.0.0 metric 4294967295/4294967295 not found Dmin is 4294967295
--此句代表沒有找到172.16.3.0/30 的可行後繼
*Mar 1 00:06:00.423: DUAL: Peer total 2 stub 0 template 2
*Mar 1 00:06:00.423: DUAL: Dest 172.16.3.0/30 entering active state.
--172.16.3.0/30 變爲active狀態，代表尋找到改網絡的新的路徑，不在拓撲表中查找
*Mar 1 00:06:00.423: DUAL: Set reply-status table. Count is 2.
*Mar 1 00:06:00.423: DUAL: Not doing split horizoni
*Mar 1 00:06:00.423: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 172.16.3.2 (Serial0/0) is down: interface down
--收不到Hello包，所以鏈路另外一邊的端口標誌爲down
*Mar 1 00:06:00.423: DUAL: linkdown: start - 172.16.3.2 via Serial0/0
--此鏈路down
*Mar 1 00:06:00.423: DUAL: Destination 10.0.0.0/8
--Destination 10.0.0.0/8不可達
*Mar 1 00:06:00.423: DUAL: Find FS for dest 10.0.0.0/8. FD is 2297856, RD is 2297856
--此句代表爲10.0.0.0/8尋找可行後繼，
*Mar 1 00:06:00.423: DUAL: 172.16.3.2 metric 4294967295/4294967295
--這個鏈路已經不行了，所以不會成爲FS
*Mar 1 00:06:00.423: DUAL: 192.168.10.6 metric 2809856/2297856 not found Dmin is 2809856
--RD爲2297856 =FD,so，也不行
*Mar 1 00:06:00.423: DUAL: Peer total 1 stub 0 template 1
*Mar 1 00:06:00.423: DUAL: Dest 10.0.0.0/8 entering active state.
--active，查找新的路徑
*Mar 1 00:06:00.423: DUAL: Set reply-status table. Count is 1.
*Mar 1 00:06:00.423: DUAL: Not doing split horizon
*Mar 1 00:06:00.423: DUAL: Destination 192.168.10.0/24
*Mar 1 00:06:00.423: DUAL: Removing dest 192.168.10.0/24, nexthop 172.16.3.2, infosource 172.16.3.2
--移除改信息，這條信息存在於這張拓撲表，使用show ip eigrp topology all-links查看，本代碼的最後部分有該表。
--
--以下類似的過程，將不再贅述
--
*Mar 1 00:06:00.423: DUAL: Destination 192.168.10.4/30
*Mar 1 00:06:00.423: DUAL: Destination 192.168.1.0/24
*Mar 1 00:06:00.423: DUAL: Removing dest 192.168.1.0/24, nexthop 172.16.3.2, infosource 172.16.3.2
*Mar 1 00:06:00.423: DUAL: Destination 192.168.10.8/30
*Mar 1 00:06:00.423: DUAL: Destination 172.16.0.0/16
*Mar 1 00:06:00.423: DUAL: Destination 172.16.1.0/24
*Mar 1 00:06:00.423: DUAL: Destination 172.16.2.0/24
*Mar 1 00:06:00.423: DUAL: Find FS for dest 172.16.2.0/24. FD is 2172416, RD is 2172416
*Mar 1 00:06:00.423: DUAL: 172.16.3.2 metric 4294967295/4294967295 not found Dmin is 4294967295
*Mar 1 00:06:00.423: DUAL: Peer total 1 stub 0 template 1
*Mar 1 00:06:00.423: DUAL: Dest 172.16.2.0/24 entering active state.
*Mar 1 00:06:00.423: DUAL: Set reply-status table. Count is 1.
*Mar 1 00:06:00.423: DUAL: Not doing split horizon
*Mar 1 00:06:00.423: DUAL: Destination 172.16.3.0/30
*Mar 1 00:06:00.423: DUAL: Clearing handle 0, count now 1
*Mar 1 00:06:00.423: DUAL: linkdown: finish
*Mar 1 00:06:00.491: DUAL: dest(172.16.3.0/30) active
*Mar 1 00:06:00.495: DUAL: rcvreply: 172.16.3.0/30 via 192.168.10.6 metric 4294967295/4294967295
*Mar 1 00:06:00.499: DUAL: reply count is 1
*Mar 1 00:06:00.499: DUAL: Clearing handle 1, count now 0
*Mar 1 00:06:00.499: DUAL: Freeing reply status table
*Mar 1 00:06:00.499: DUAL: Find FS for dest 172.16.3.0/30. FD is 4294967295, RD is 4294967295 found
*Mar 1 00:06:00.499: DUAL: Removing dest 172.16.3.0/30, nexthop 0.0.0.0, infosource 0.0.0.0
*Mar 1 00:06:00.499: DUAL: Removing dest 172.16.3.0/30, nexthop 192.168.10.6, infosource 192.168.10.6
*Mar 1 00:06:00.499: DUAL: No routes. Flushing dest 172.16.3.0/30
--查找後沒有到達該網絡的路徑，刪除該網絡在路由表中的信息
*Mar 1 00:06:00.499: DUAL: rcvreply: 10.0.0.0/8 via 192.168.10.6 metric 2809856/2297856
--接收到192.168.10.6發來的響應，他可以到達10.0.0.0/8，RD=2297856
*Mar 1 00:06:00.499: DUAL: reply count is 1
*Mar 1 00:06:00.499: DUAL: Clearing handle 1, count now 0
*Mar 1 00:06:00.499: DUAL: Freeing reply status table
*Mar 1 00:06:00.499: DUAL: Find FS for dest 10.0.0.0/8. FD is 4294967295, RD is 4294967295 found
*Mar 1 00:06:00.503: DUAL: Removing dest 10.0.0.0/8, nexthop 172.16.3.2, infosource 172.16.3.2
*Mar 1 00:06:00.507: DUAL: RT installed 10.0.0.0/8 via 192.168.10.6
--因爲該鏈路的RD=2297856 < FD，因此該路由成爲了successor router【後繼路由】，
--添加到拓撲表和路由表中，可在下面的拓撲表與路由表查看
*Mar 1 00:06:00.507: DUAL: Send update about 10.0.0.0/8. Reason: metric chg
*Mar 1 00:06:00.511: DUAL: Send update about 10.0.0.0/8. Reason: new if
--把更新發給鄰居
*Mar 1 00:06:00.515: DUAL: dest(172.16.2.0/24) active
*Mar 1 00:06:00.515: DUAL: rcvreply: 172.16.2.0/24 via 192.168.10.6 metric 4294967295/4294967295
*Mar 1 00:06:00.515: DUAL: reply count is 1
*Mar 1 00:06:00.515: DUAL: Clearing handle 1, count now 0
*Mar 1 00:06:00.515: DUAL: Freeing reply status table
*Mar 1 00:06:00.515: DUAL: Find FS for dest 172.16.2.0/24. FD is 4294967295, RD is 4294967295 found
*Mar 1 00:06:00.515: DUAL: Removing dest 172.16.2.0/24, nexthop 172.16.3.2, infosource 172.16.3.2
*Mar 1 00:06:00.519: DUAL: Removing dest 172.16.2.0/24, nexthop 192.168.10.6, infosource 192.168.10.6
*Mar 1 00:06:00.523: DUAL: No routes. Flushing dest 172.16.2.0/24
*Mar 1 00:06:02.351: %LINK-5-CHANGED: Interface Serial0/0, changed state to administratively down
*Mar 1 00:06:03.351: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/0, changed state to down
Router(config-if)#do sh ip route
--在全局模式下，使用do + 特權模式命令，就是在特權模式下執行的結果
Codes: C - connected, S - static, 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
i - IS-IS, su - IS-IS summary, 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
Gateway of last resort is not set
192.168.10.0/24 is variably subnetted, 3 subnets, 2 masks
D 192.168.10.0/24 is a summary, 00:08:53, Null0
C 192.168.10.4/30 is directly connected, Serial0/1
D 192.168.10.8/30 [90/2681856] via 192.168.10.6, 00:08:53, Serial0/1
172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks
D 172.16.0.0/16 is a summary, 00:08:53, Null0
C 172.16.1.0/24 is directly connected, FastEthernet1/0
D 10.0.0.0/8 [90/2809856] via 192.168.10.6, 00:05:47, Serial0/1
D 192.168.1.0/24 [90/2172416] via 192.168.10.6, 00:08:54, Serial0/1
Router(config-if)#do sh ip eigrp topology
IP-EIGRP Topology Table for AS(1)/ID(192.168.10.5)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
r - reply Status, s - sia Status
P 10.0.0.0/8, 1 successors, FD is 2809856
via 192.168.10.6 (2809856/2297856), Serial0/1
P 192.168.10.0/24, 1 successors, FD is 2169856
via Summary (2169856/0), Null0
P 192.168.10.4/30, 1 successors, FD is 2169856
via Connected, Serial0/1
P 192.168.1.0/24, 1 successors, FD is 2172416
via 192.168.10.6 (2172416/28160), Serial0/1
P 192.168.10.8/30, 1 successors, FD is 2681856
via 192.168.10.6 (2681856/2169856), Serial0/1
P 172.16.0.0/16, 1 successors, FD is 28160
via Summary (28160/0), Null0
P 172.16.1.0/24, 1 successors, FD is 28160
via Connected, FastEthernet1/0
總結：172.16.2.0/24，172.16.3.0/24，的信息在路由表及拓撲表中刪除，當然鄰居表裏172.168.3.2/24的信息也會刪除。10.0.0.0/8依然可達，有關信息將會更新。
Router(config-if)#no shut
Router(config-if)# !啓用
*Mar 1 00:21:50.191: %LINK-3-UPDOWN: Interface Serial0/0, changed state to up
*Mar 1 00:21:50.215: DUAL: dest(172.16.3.0/30) not active
--取消active標誌，變爲passive
*Mar 1 00:21:50.219: DUAL: rcvupdate: 172.16.3.0/30 via Connected metric 2169856/0
--意味着要建立鄰居關係
*Mar 1 00:21:50.223: DUAL: Find FS for dest 172.16.3.0/30. FD is 4294967295, RD is 4294967295 found
*Mar 1 00:21:50.223: DUAL: RT installed 172.16.3.0/30 via 0.0.0.0
*Mar 1 00:21:50.227: DUAL: Send update about 172.16.3.0/30. Reason: metric chg
*Mar 1 00:21:50.231: DUAL: Send update about 172.16.3.0/30. Reason: new if
--DUAL計算後，RD<FD,添加到路由表，並且通知鄰居
*Mar 1 00:21:50.231: DUAL: lostroute: do nothing
--代表建立鄰居失敗，原因在下面這一句
*Mar 1 00:21:51.195: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/0, changed state to up
--數據鏈路up
*Mar 1 00:21:52.095: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 172.16.3.2 (Serial0/0) is up: new adjacency
--與172.16.3.2建立鄰居關係
*Mar 1 00:21:52.143: DUAL: dest(172.16.2.0/24) not active
*Mar 1 00:21:52.147: DUAL: rcvupdate: 172.16.2.0/24 via 172.16.3.2 metric 2172416/28160
*Mar 1 00:21:52.147: DUAL: Find FS for dest 172.16.2.0/24. FD is 4294967295, RD is 4294967295 found
*Mar 1 00:21:52.151: DUAL: RT installed 172.16.2.0/24 via 172.16.3.2
*Mar 1 00:21:52.155: DUAL: Send update about 172.16.2.0/24. Reason: metric chg
*Mar 1 00:21:52.159: DUAL: Send update about 172.16.2.0/24. Reason: new if
*Mar 1 00:21:52.159: DUAL: dest(10.0.0.0/8) not active
*Mar 1 00:21:52.163: DUAL: rcvupdate: 10.0.0.0/8 via 172.16.3.2 metric 2297856/128256
*Mar 1 00:21:52.163: DUAL: Find FS for dest 10.0.0.0/8. FD is 2809856, RD is 2809856
*Mar 1 00:21:52.163: DUAL: 192.168.10.6 metric 2809856/2297856
*Mar 1 00:21:52.163: DUAL: 172.16.3.2 metric 2297856/128256 found Dmin is 2297856
--172的RD<192的 RD<FD,所以172是後繼路由，192是FS
*Mar 1 00:21:52.163: DUAL: RT installed 10.0.0.0/8 via 192.168.10.6
*Mar 1 00:21:52.163: DUAL: RT installed 10.0.0.0/8 via 172.16.3.2
--添加到拓撲表，172同時進入路由表
*Mar 1 00:21:52.163: DUAL: Send update about 10.0.0.0/8. Reason: metric chg
*Mar 1 00:21:52.163: DUAL: Send update about 10.0.0.0/8. Reason: new if
*Mar 1 00:21:52.163: DUAL: dest(192.168.10.0/24) not active
*Mar 1 00:21:52.163: DUAL: rcvupdate: 192.168.10.0/24 via 172.16.3.2 metric 2681856/2169856
*Mar 1 00:21:52.163: DUAL: Find FS for dest 192.168.10.0/24. FD is 2169856, RD is 2169856
*Mar 1 00:21:52.163: DUAL: 0.0.0.0 metric 2169856/0
*Mar 1 00:21:52.163: DUAL: 172.16.3.2 metric 2681856/2169856 found Dmin is 2169856
*Mar 1 00:21:52.163: DUAL: RT installed 192.168.10.0/24 via 0.0.0.0
*Mar 1 00:21:52.163: DUAL: dest(192.168.1.0/24) not active
*Mar 1 00:21:52.163: DUAL: rcvupdate: 192.168.1.0/24 via 172.16.3.2 metric 2684416/2172416
*Mar 1 00:21:52.163: DUAL: Find FS for dest 192.168.1.0/24. FD is 2172416, RD is 2172416
*Mar 1 00:21:52.163: DUAL: 192.168.10.6 metric 2172416/28160
*Mar 1 00:21:52.163: DUAL: 172.16.3.2 metric 2684416/2172416 found Dmin is 2172416
*Mar 1 00:21:52.163: DUAL: RT installed 192.168.1.0/24 via 192.168.10.6
Router(config-if)#do sh ip route
Codes: C - connected, S - static, 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
i - IS-IS, su - IS-IS summary, 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
Gateway of last resort is not set
192.168.10.0/24 is variably subnetted, 3 subnets, 2 masks
D 192.168.10.0/24 is a summary, 00:02:40, Null0
C 192.168.10.4/30 is directly connected, Serial0/1
D 192.168.10.8/30 [90/2681856] via 192.168.10.6, 00:21:37, Serial0/1
172.16.0.0/16 is variably subnetted, 4 subnets, 3 masks
D 172.16.0.0/16 is a summary, 00:21:37, Null0
C 172.16.1.0/24 is directly connected, FastEthernet1/0
D 172.16.2.0/24 [90/2172416] via 172.16.3.2, 00:02:40, Serial0/0
C 172.16.3.0/30 is directly connected, Serial0/0
D 10.0.0.0/8 [90/2297856] via 172.16.3.2, 00:02:42, Serial0/0
D 192.168.1.0/24 [90/2172416] via 192.168.10.6, 00:02:42, Serial0/1
Router(config-if)#do show ip eigrp topology
IP-EIGRP Topology Table for AS(1)/ID(192.168.10.5)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
r - reply Status, s - sia Status
P 10.0.0.0/8, 1 successors, FD is 2297856
via 172.16.3.2 (2297856/128256), Serial0/0
P 192.168.10.0/24, 1 successors, FD is 2169856
via Summary (2169856/0), Null0
P 192.168.10.4/30, 1 successors, FD is 2169856
via Connected, Serial0/1
P 192.168.1.0/24, 1 successors, FD is 2172416
via 192.168.10.6 (2172416/28160), Serial0/1
P 192.168.10.8/30, 1 successors, FD is 2681856
via 192.168.10.6 (2681856/2169856), Serial0/1
P 172.16.0.0/16, 1 successors, FD is 28160
via Summary (28160/0), Null0
P 172.16.1.0/24, 1 successors, FD is 28160
via Connected, FastEthernet1/0
P 172.16.2.0/24, 1 successors, FD is 2172416
via 172.16.3.2 (2172416/28160), Serial0/0
P 172.16.3.0/30, 1 successors, FD is 2169856
via Connected, Serial0/0
Router(config-if)#do show ip eigrp topology all-links
IP-EIGRP Topology Table for AS(1)/ID(192.168.10.5)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
r - reply Status, s - sia Status
P 10.0.0.0/8, 1 successors, FD is 2297856, serno 22
via 172.16.3.2 (2297856/128256), Serial0/0
via 192.168.10.6 (2809856/2297856), Serial0/1
P 192.168.10.0/24, 1 successors, FD is 2169856, serno 13
via Summary (2169856/0), Null0
via 172.16.3.2 (2681856/2169856), Serial0/0
P 192.168.10.4/30, 1 successors, FD is 2169856, serno 10
via Connected, Serial0/1
P 192.168.1.0/24, 1 successors, FD is 2172416, serno 14
via 192.168.10.6 (2172416/28160), Serial0/1
via 172.16.3.2 (2684416/2172416), Serial0/0
P 192.168.10.8/30, 1 successors, FD is 2681856, serno 15
via 192.168.10.6 (2681856/2169856), Serial0/1
P 172.16.0.0/16, 1 successors, FD is 28160, serno 11
via Summary (28160/0), Null0
P 172.16.1.0/24, 1 successors, FD is 28160, serno 1
via Connected, FastEthernet1/0
P 172.16.2.0/24, 1 successors, FD is 2172416, serno 21
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
r - reply Status, s - sia Status
via 172.16.3.2 (2172416/28160), Serial0/0
P 172.16.3.0/30, 1 successors, FD is 2169856, serno 20
via Connected, Serial0/0
總結：
收斂快。