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Route planning search process |
| Author： Date：2016/7/20 10:42:03 |
We know that the process of routing lookup is to find the next hop of the data packet process! IP route hop by hop packets sent to the destination. So-called next hop is and their directly connected to a router corresponding interface IP address. This is sensible understanding. However, IP routing provides also a way, namely next hop without have to own and direct, it can ignore the router topology around, directly inform the relatively distant topology
At Server the next hop is R2, arrived at R2 the next hop is R1 and so on... Protocol stack routing lookup logic in the routing lookup, if it is found that the NextHop is not and their directly connected, so will the the NextHop as destination again according to the logical routing lookup table until found and their direct NextHop or complete failure so far. This route is equivalent to the NextHop into the distance. The recursive lookup can bring what benefit?? obviously, recursive routing can NextHop is near the topology of the network changes to minimize the influence of! For must use static routing, reasonable planning of recursive routing can be greatly simplified static routing maintenance workload, of course, if you use dynamic routing, it is not necessary, to know the recursive routing in bringing convenience maintenance, the cost is router to increase the lookup pressure.
Is through the link, imagine if the arrival of R1 and R2 are a problem, and now need to N1, N2, N3 NextHop switch to R7, you also need to modify the three routing (unable to achieve routing aggregation, more bad). However, if we already know that reaches N1, N2, N3 to R3, then it can be configured to N1, N2, N3 NextHop for R3, immediately in the logic to bypass the link, in fact, the protocol stack routing lookup logic helps administrators to find a reach of R3, the final NextHop or and R0 directly connected, a recursive lookup end conditions destination and R0 directly connected. In the configuration, addressing the needs of the 3 networks into addressing the needs of R3, the configuration is also simplified a lot, you only need to configure a default gateway can be changed when the link switch configuration is also a lot less.
Remember, however, recursive routing did not change any packets arrive at the destination network path, it will eventually have to be implemented in a direct NextHop, if we based on backstepping recursive routing configuration, then it can be a non recursive "normal" routing configuration, the normal routing configuration can also solve the problem of the complicated configuration, so recursive routing to some extent is a lazy approach. In addition, the use of recursive routing has a point, that is, you must be familiar with the network topology, the reason to use recursive routing to steer clear of the constantly changing link, and as a static routing, link change means all related routing must be re configuration and use recursive routing can reduce the workload of configuration, whether to use recursive routing a tradeoff point is: if the arrival of a target network link in the on the way can not converge into fewer target network link, recursive routing there is no meaning. |