[HCIA continuous update] advanced features of routing

Advanced features of routing

Route recursion

1、 The route must have a direct next hop to guide forwarding , However, when generating a route, the next hop may not be directly connected , Therefore, it is necessary to calculate the next hop of a direct connection and the corresponding outgoing interface , This process is called routing recursion

2、 Route recursion is also called route iteration

Equivalent route

There are equivalent routes in the routing table , Go to the destination network IP The message router will pass through all effective interfaces 、 Next hop forwarding , This forwarding behavior is called load sharing

Floating route

Basic concepts

1、 Static routing supports manual priority assignment during configuration , You can configure the destination address / Same mask 、 Different priorities 、 Next hop different static routes , Backup the forwarding path

2、 Floating route is the backup of primary , Ensure that backup routes are provided in case of link failure . When the primary route reaches the next hop, the backup route will not appear in the route table

Example

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Route summary

CIDR

1、CIDR use IP Address plus mask length to identify network and subnet , Instead of following tradition A、B、C And other types of network addresses

2、CIDR Allow mask length of any length , take IP Address as a continuous address space , Prefixes of any length can be used to assign , Multiple consecutive prefixes can be aggregated into a network , This feature can effectively reduce the number of routing table entries

Routing convergence requirements

1、 Subnet partition 、VLSM It solves the waste of address space , But it also brings new problems ; The number of routing entries in the routing table increases

2、 In order to reduce the number of route entries, you can use route summary

Introduction to routing summary

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Summary calculation

1、 Based on a series of continuous 、 Regular IP Network segment , If It is necessary to calculate the corresponding route summary , And ensure that the resulting Huizhong route is just “ Include ” Aforementioned IP Network segment , It is necessary to ensure that the mask length of the summary route is as long as possible

2、 The trick is ： Convert the destination network addresses of detailed routes into binary , Then arrange them , Find all destination network addresses “ Same bit ”

Accurately summarize