routing
What is routing
From the source host to the destination of the forwarding process (source IP remains unchanged, the source follower MAC transmission device varies)
action is able to forward packets to the correct destination, and select the best route during forwarding device (by Routing table forwarding).
Determine the end-to-end network range and work at the network layer .
Criteria for choosing the best route
*The most preferred match with the longest subnet mask length* The most preferred match with the lowest priority in the
routing protocol is selected
| DIERECT ： 0 | OSPF：10 |
|---|---|
| IS-IS：15 | STATIC：60 |
| RIP：100 | OSPF ASE：150 |
| EBGP：256 | OSPF NSSA：150 |
| IBGP：256 |
*In the case of the same routing protocol: select the most preferred match with the smallest metric value. The metric value defined by each protocol is different. Static routing is related to the routing priority. This is manually specified. The RIP protocol is related to the number of hops. The smaller the number, the higher the priority. The OSPF protocol is related to broadband, and the largest bandwidth has the highest priority. The metric is used to determine the quality of the link.
*If none of the above routes can be matched, the default route is matched.
Routing table
* The collection of routing entries maintained in the router
* The router makes path selection according to the routing table
* For non-directly connected network segments, static routing or dynamic routing is required, and the network segment is added to the routing table
Floating routing
Floating routing refers to the configuration of two static routes. By default, the link with high quality (large bandwidth) is selected as the main path. When the path fails, the backup route with smaller bandwidth will replace it, keeping the network uninterrupted and improving reliability .
Default route
Match all network segments.
The default route is a special form of static route. It belongs to a kind of static route. It is conditional to use it and can only be used in the stub network.
When the router cannot find the routing entry of the target network in the routing table, the router forwards the request to the default routing interface.
When to use the default route
The default route is used in the stub network . When there is only one outlet in the network that can connect to the external network, the default route is used. The data of any destination address inside the network is sent out through the default route. Using the default route in the stub network can simplify the routing table , reduce the time for the router to forward data to look up the routing table, and improve network performance.