Rip notes [rip three timers, the role of horizontal segmentation, rip automatic summary, and the role of network]

Catalog

Horizontal segmentation  

rip Three timers of

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Omit Loop Interface and interface IP To configure

RIP Basic configuration .network There is an open interface rip Meaning of function , therefore nerwork 1.0.0.0 It's actually on Loop 0 And Loop 1 Two interfaces RIP function .

R1
 rip 1
 version 2
 network 192.168.1.0
 network 1.0.0.0
 network 2.0.0.0

R2
rip 1
 version 2
 network 192.168.1.0

The above command routes two direct connections to all interfaces RIP Functions are turned on , Now let's use dis ip rou Check it out. R2 The routing table for

Pass the above figure , You can see R2 Now there is Loop 0   Loop 1  Loop2 All routing information , But we all know RIPv2 The default is to turn on automatic route summary . According to this idea ：R2 There should be no 1.1.1.0/24 And 1.1.2.0/24 Two routing messages , It should be 1.0.0.0/8 A routing message , So what's going on ？

We go through dis rip 1 interface verbose see R1 Of RIP Interface information ：

Horizontal segmentation  

You can see   Split-Horizon Horizontal segmentation It's open , Horizontal segmentation will lead to RIP No automatic summary . therefore R2 You'll see 1.1.1.0/24 、1.1.2.0/24 Two routing messages . Now we close R1 Horizontal segmentation function .[ The principle of horizontal segmentation is to accept RIP Interface of routing information , When announcing routing information externally, it will not be received from this interface RIP Route information is announced , A simple example ：R2 adopt G0/0/0 Interface received R1 Of 1.1.1.0/24 And 1.1.2.0/24、2.2.2.2/24 After three routing messages ,R2 The announced routing table information will not carry these three routing information ]

[Huawei-GigabitEthernet0/0/0]  undo rip split-horizon   # close G0/0/0 Horizontal segmentation function of interface , The function is as above

now Shut down the R1G0/0/0 Horizontal segmentation function , Again Check it out. R2 The routing table for ：

rip Three timers of

Find out ,R2 Only 1.0.0.0/8 A routing message , however Turning off horizontal segmentation is not a wise move , Its harm is as follows ： We know RIP There are three timers ： Update the timer 【 The default is 30s A cycle , And 30 An announcement of routing information is also called flooding 】;   Aging timer 【 The default is 180s; Every one of them RIP Routing information has an aging calculator , And in 30 In a flood , Time again after receiving the routing information . When the timer reaches 180 after , The routing information corresponding to this timer will be deleted from the routing table , When it still exists in the router, it is only marked as unreachable 】;  Garbage collection timer 【 The default is 120s, When the aging timer reaches 180s After that, the garbage collection timer will be started , During the timing , If received, it will be deleted by the routing table The updated information of the route will recycle the route to the route table , And continue to start the aging timer . If 120s There is still no update information of this route , Then completely delete the routing information from the router .】

For the first R2 establish LOOP 4 Simulate the external network ：

If R2 Of Loop4 Become inaccessible 【R4 I know it , Because it is direct connection routing information 】,R2 Will LOOP4 The routing information of is deleted from its own routing table 【R2 Not yet RIP Time of announcement , therefore loop4 And non derivable routing information pairs R1 I don't know ,R1 Think LOOP 4 It can still pass R2 arrive 】 If at this time R1 Of RIP The update just arrived ,R1 Will include their own routing information LOOP 4 The routing information of is announced . that R2 Will think loop4 It can still pass R1 arrive , therefore R2 Will be able to Loop 4 The next hop address is R1. and R1 The information in the routing table thinks LOOP4 It's through R2 Arrived at , This creates a loop .

in summary ： close R1 The horizontal segmentation of is obviously not feasible , Then we can use other methods to achieve routing summary

First reopen the horizontal split , stay rip 1 Input in summary always To complete automatic summary . Keep looking at R2 See the effect of the routing table ：

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