Run and verify the Routing Protocol

In the previous section, we briefly introduced the network routing protocol for VPN. Through this article, I think you have mastered this concept. Now let's analyze its running status. First, let's talk about running. Vrouters that initially run the OSPF routing protocol must go through the process of finding neighbors, understanding networks, and selecting routes. In this process, three independent tables are created simultaneously: lists the neighbor tables of neighboring routers, the topology tables that describe the network structure, and the route tables. These three tables are updated when the network in the Operation changes ｡

1. Establish adjacent relationships

The vro running the OSPF routing protocol starts to run, the multicast address is used to send a HELLO packet from each interface that participates in the OSPF routing protocol. When the router receives the first HELLO packet from a neighboring router, send back an update package in single-point transmission mode. After receiving confirmation from the peer router about the update package, both parties establish a neighbor relationship ｡

2. Find the network topology and select the shortest route

When a router dynamically discovers a new neighbor, it also obtains the route information advertised by the new neighbor. The router first compares the route update information obtained with the information recorded in the topology table, A route that meets the feasible conditions is placed in the topology table, and then added to the route table through the route table of the successor router, if the route through the feasible successor router is within the configured range of non-equal cost routing load balancing, it is also added to the route table. Otherwise, save it in the topology table as the alternative route. If the router learns multiple routes to the same destination through different routing protocols, the Management Distance of the routes is compared, the route with the minimum management distance is the optimal route ｡

3. Route query and update

When the route information does not change, the OSPF neighbor only sends a HELLO packet to maintain the neighbor relationship to reduce the usage of network bandwidth. When a neighbor is lost or a link is unavailable, then, the system immediately finds a feasible successor Router from the topology table and enables the alternative route. If there is no successor router in the topology table, because the neighbor of the router is used to provide route information, send query data packets to all neighbors after the route is set to active ｡

If a neighbor has a route entry to the destination, it will reply to the query and no longer spread the query. Otherwise, it will further query each of its neighbors, only after all the queries are answered will the routing protocol re-calculate the route and select a new successor router ｡

4. Verify the run of the MongoDB instance.

In the network topology shown in, the vroeigrp performs the basic configuration of the VPN gateway. All vrouters belong to the Autonomous System 1 of the VPN gateway and no other routing protocols are configured, we use the information obtained by running the relevant commands of the command to verify the running of the command ｡

Let's take vror2 R2 as an example to verify how to understand the network and select a route using the VPN protocol ｡

For the destination 192.168.1.0 and 172.16.1.4, router R2 receives the route advertised by its two neighboring routers R3 (10.1.1.3) and R4 (172.16.1.2) respectively. The shortest route to the destination 192.168.1.0 is through R3, the feasible distance is 20563200, but the advertised distance (281600) of R4 is smaller than the feasible distance, which meets the feasible conditions, therefore, R4 is the feasible successor router of the route. the shortest route to the destination 172.16.1.4 is through R3, the feasible distance is 20537600, And the advertised distance (20537600) through R4 is equal to (Note: not less) the feasible distance does not meet the feasible conditions. Therefore, R4 cannot be the feasible successor router of the route ｡

By default, it is the Server Load balancer on the same cost route. Therefore, only one route entry to the destination 192.168.1.0 in the routing table is routed through the router R3 (10.1.1.3), and the standby route entry (R4) the route is saved in the topology table. Because the route is learned through the internal MongoDB, the routing management distance is 90. If non-cost load balancing is configured, the Standby route is also added to the route table ｡

Finally, we need to emphasize that, because the OSPF protocol is a private route protocol of Cisco, all the content discussed in this article is based on the router of Cisco ｡