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1.Router 5 新加上一個網段，Router3 的路由表中何時新增一筆 路由資訊
每30秒更新一次路由表  30秒後Router3 路由表新增了192.168.120.0的資訊!!
 

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2. 192.168.10.0 網段故障，Router 5 何時顯示possibly down
192.168.10.0在3分鐘後，馬上出現possibly down!!

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3. 192.168.10.0 網段故障，Router 5 的該筆路由資訊何時會被移除
Router5中的192.168.10.0先出現possibly down!! 然後又再4分鐘後，立刻被移除掉資訊

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Rip 的時間:
1. Periodically sending the routing table to neighbors: 30 秒.
2. Invalid Timer:  如果對方於 180秒內均無回應,則視為 Invalid router,但該Route 仍存在於 Route table.
3. Flush Timer: 如果 Invalid Router 持續 超過 240 秒,則該Route 將會被 Route Table 移除.
4. Holddown Timer:  持續未回應180秒到 240秒間的時間稱為 Holddown Timer: 如果 cost 較少的會被接受,而Cost較高者不會被接受.

Rip 重要的問題:
1. Class Ful : 故無法支援 VLSM(Variable Length Subnet Mask): 切子網段
CIDR(Classless Inter-Domain Routing): 合併子網段成一個網段.
2.不支援不連續網段:
3.會自動作子網 summary: 其目的在減少Route Table 的Rule.但容易造成Loading balance 的錯誤.
4. Rip 使用 UDP 520 Port , 使用 Boardcast 傳送 全部 route 的資料.
     RIP2 則使用  Multicast (224.0.0.9)
     Eigrp 則使用 Multicast(224.0.0.10)
     Ospf   在 DbOther 找 DBRoot 則使用(224.0.0.6)
                 而 DbRoot在回覆給 DBOther 時使用 (224.0.0.5)
     Max Hop Counte  則為 15,超過則視為不可到逹.
5. Rip I 可以接收 Rip I 及 Rip II 的封包,而 Rip II 只可以接受 Rip II 的封包.
6. Rip I 在傳送 Update 給其它 Router 時,會依下列規則:
     1. 如所經過的網段為同個網段(Same Major Network),則其subnet mask 會帶過去.
     2. 如所經過的網段為非同個網段時,則只會帶 Classful 的 subnet mask 過去.
     3. 所以如為不連續網段,則會造成 Equal cost load balance 的錯誤情況.
7. Rip I 及 Rip II 每個Update 封包可以帶最多 25個route rules.

 

 


http://www.ciscoccnabootcamp.com/ccna-routing-and-switching/rip/timers/
 
RIP timers are update, invalid, holddown, and flush. The update timer is the amount of time at which the router sends RIP updates. By default, RIP updates are sent every 30 seconds. The invalid timer specifies the amount of time that the router should wait before it considers a specific route as invalid. This means, if the router did not receive a RIP update including a specific route “X” within the invalid time interval after the last update( including the “X” route), then the route “X” will be marked as invalid. The holddown timerdetermines the amount of time that the router should wait before accepting new routing information about an unreachable route. The flush timer defines the amount of time that router will wait before removing an invalid route from the routing table.

To change one or all of these timers, use the timers basic command. The timers basic command has the following syntax:

timers basic update invalid holddown flush

The default values for the update, invalid, holddown, and flush parameters are 30 seconds, 180 seconds, 180 seconds, and 240 seconds, respectively. This command was introduced in the Cisco IOS Software Release 10.0.

The following configuration sets the values of update, invalid, holddown, and flush timers on a router named R1 to 10 seconds, 60 seconds, 60 seconds, and 80 seconds, respectively.

R1(config)#router rip
R1(config-router)#version 2
R1(config-router)#network 10.0.0.0
R1(config-router)#network 140.1.0.0
R1(config-router)#no auto-summary
R1(config-router)#timers basic 10 60 60 80
R1(config-router)#^Z
R1#

To verify our configuration, we’ll use the show ip protocols command in the privileged EXEC mode.

R1#show ip protocols
Routing Protocol is "rip"
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
Sending updates every 10 seconds, next due in 6 seconds
Invalid after 60 seconds, hold down 60, flushed after 80
Redistributing: rip
Default version control: send version 2, receive version 2
Interface Send Recv Triggered RIP Key-chain
FastEthernet0/0 2 2
FastEthernet0/1 2 2
Serial1/2 2 2
Automatic network summarization is not in effect
Maximum path: 4
Routing for Networks:
10.0.0.0
140.1.0.0
Routing Information Sources:
Gateway Distance Last Update
Distance: (default is 120)

R1#

Keep in mind that short update timer can cause congestion over show-speed serial links.

 

 

 

 

 

 

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