Common tips for solving problems in the CCIE exam: the principle of routing re-release

  •     SPOTO
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  •   Posted on: 2019-04-22
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  • CCIE Written

Routing re-release can be a tricky thing, and it is easy to generate the following traps:


Trap 1

Routing loops - related to how to implement re-release, routers may send routing information learned from an autonomous system back to the same autonomous system.

Feedback is similar to the horizontal segmentation problem that occurs in distance vector routing techniques;


Trap 2

Incompatibility of routing information - Each routing protocol uses different metrics to determine the best path.

Because the metrics of the route cannot be accurately translated into the metrics used by different routing protocols, it may not be optimal for the router to redistribute the selected path;


Trap 3

Convergence times are inconsistent - different routing protocols converge at different rates.

For example, the PIP protocol converges slower than EIGRP, so if there is a link failure, the EIGRP network will learn this failure before the RIP network.



These potential points of failure can be avoided through careful planning and implementation. Be sure to follow these important guidelines when configuring route redistribution:


Principle 1

Skilled network – because there are many ways to implement re-release, understanding the network to be re-released will help us make the best decisions;


Principle 2

Do not use routing protocols overlappingly - do not use two different protocols in the same interconnected network. Instead, there must be clear boundaries between networks using different protocols;


Principle 3

Use one-way re-distribution in the presence of multiple border routers—if more than one router is used for route redistribution, route re-distribution should be performed in only one direction to avoid routing loops and different convergence times. The problem that comes with it. Consideration should be given to using default routes in domains that do not inject external routes;


Principle 4

Use two-way re-release on a single border router—two-way re-release can work well in an environment where only route redistribution is configured on one router in the network.

If there are multiple route redistribution nodes, do not use two-way re-release unless there is another technique that reduces the chances of routing loops.

A combination of techniques such as default routing, route filtering, and management distance modification can be used to eliminate routing loops...


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