I wrote in front that Tian Jie suddenly asked "What are the five anti-ring mechanisms of RIP ?"
As it was suddenly attacked, I was quite impressed. First, paste the answer: "1. horizontal segmentation; 2. Maximum 16 hops; 3. Route poisoning; 4. Toxicity reversal; 5. Inhibition timer ." First, "what is
Loop?" WHAT) Let's look at a scenario: It explains the principle of RIP route update)
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Normally, assume that a PC with the IP address 192.168.1.1/24 is directly connected to R1, then the metric value from R1 to PC is 0. Then R1 and R2 run the "RIP" protocol, then R1 will put all its own routes through the"
ResponsePacket "sent to R2, of course, these packets must include the route to the PC. R2 obtains"
ResponseA route entry to the PC does not exist, so it adds the route information to its route table, and the value of "metric" is + 1. In this way, R2 has a route from one day to the PC with the IP address "192.168.1.1/24" and the metric value is 2. But at this time, the PC and the router are connected
This line suddenly brokeR1 loses its connection with the PC, and it also loses the "direct connection route to the PC ". However, due to the periodic update mechanism of RIP,
30 s later, R2 will send a "Response packet", which contains all the routes owned by R2. of course, the"
The route to the PC". R1 was very happy to see this route at this time! See old friends,
Because you have noThen, I learned the message from the neighbor, so I took the route and paid attention to the metric value + 1, the metric value from R1 to PC is "2 "). So,
30 s passed again. R1 also needs to issue a "Response" packet to inform everyone of the routes it owns (including the routes to the PC, although the connection between it and the PC has been broken). At this time, r2 received the R1 packet again. Open it and check it. There is a route to the PC,
But how does its metric value change to "2"? Since
The original PC route is what R1 told meThere may be conflicts between them.
Their ownThing, I
Just add "metric value + 1"In this case, the metric value above R2 is 3 ). And then 30 S, R1 continues to add, and then 30 S, R2 plus... When can this problem be solved? Of course, this is not the most difficult thing. At this moment, R2 receives a request to access the "192.168.1.1/24" PC on the right side, R2 will definitely be directly thrown to R1, while R1 will check, isn't PC in your R2? So he threw it to r2. When R2 saw it, he thought R1 had a joke and threw it to R1. As a result, two people are always lost, and the speed is getting faster and faster. It's just a pack. What if it's just a movie? The tens of thousands of data packets directly cause R1 and R2 to crash! At this time, because the network cable basically runs on each other's lost data packets, other normal programs cannot send and receive packets normally, either freezing or crashing. In such a situation where everyone crashes together, the name is"
Loop". Fortunately, the IP package itself has a value called "TTL" Time to live). After 255 times of loss, the package was finally freed and then abandoned. However, this is difficult to understand.
This is a bit like "related departments" with Chinese characteristics ". You have to ask for A comment. Department A says, "This is not my responsibility. You should go to department B ". Department B said, "How can you contact us? This is clearly the case of Department A. You should find it ." So I had to go back to department A and be kicked to department B. Then I went back to department... One day, one department said, "Sorry, you are only valid for three months. It has been three months and one day, and we cannot manage it ". One thousand grass mud horse galloping over...Therefore, the loop is obviously not good, so we should avoid it, or destroy it. It is necessary to start from the source, and they will not be given the opportunity to shirk each other in the routing phase.
Method 1: horizontal segmentation:This method is simple and clear, that is, you R1 gave R2.
A route,
R2 will no longer route A to you.. No, no. In this way, there will be no such situation as R1 finding a long-time friend from R2. In this way, after S, refresh the timer), route A disappears from the route tables of R1 and R2. If people come to A, they will directly use the phrase "sorry, A is not here (
U) "Sent back.
Method 2: Route poisoning:This name seems awesome, but its principle is actually very small. Once R1 finds that A is gone, it immediately changes the metric value of a to 16 rip, which allows up to 15 hops. That is to say,
If the metric value is 16, the route is inaccessible.). R2 saw that A was poisoned, so he decisively abandoned. In this way, A is abandoned by R1, and then R2. then, the loop will no longer exist.
Method 3: Toxicity reversal:This is
Enhanced version of "route poisoning"In this environment, the relationship between R1 and R2. For example:
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It turns itself into a stepping stoneAnd sent the message "route A is poisoned and everyone is getting away from it" to its friends. Let everyone know that A is not reachable. In this way, we can quickly reflect and promptly drop route A from our route table.
Method 4: suppress the Timer:This is
"Probation" for Route poisoning". It is afraid that A will lose connection to R1. If the problem is solved with a kill, if it recovers in a few seconds, it will not be necessary to make an announcement again, which is troublesome. So, just give you s to suppress the timer) and wait for you. If A can return to the arms of R1 in time, R1 will not send any poisoning information. If you do not know it, it will not cause the entire network to be turbulent.
Method 5: up to 16 hops:This is the final weapon and a killer. As mentioned earlier, the maximum number of hops of RIP is 16, that is, when metric is 16, it indicates that the network is inaccessible.
If the previous "route poisoning" does not take action. Let's look back at the process of playing the ball with R1 and R2,
Each time they play a game, the metric value is + 1. When they are added to 16, the effect is equivalent to "route poisoning ".. You may think that it is so tiring to kick in the past, so if you think about the attributes of the IP itself, it is the end to be kicked "under 255! Of course, there is no way to do this, and it is also its own property. September 16, 2013 02:07:25, it's too slow for me to write things. It's time to go to bed.
