Precautions for COST configuration on vro

OSPF is a typical link-State routing protocol. It is generally used in the same routing domain. Here, a routing domain refers to an autonomous system, that is,, it refers to a group of networks that exchange route information through a unified routing policy or routing protocol.

In this AS, all OSPF routers maintain a database that describes the AS structure and stores the status information of the corresponding link in the routing domain, the OSPF router uses this database to calculate its OSPF route table.

1. After configuring the IP address and OSPF protocol for each interface, the router is configured as a frame relay switch, which helps us better understand Frame Relay. Note: In the router interface, you can define the interface type ip OSPF network broadcast or manually specify the neighbors of the two interfaces. Otherwise, the neighbors may fail.

2. Then, we can manually specify the cost value for each route interface. The command is to enter the interface: ip OSPF cost note: the default COST value for the Ethernet port is 1. The default value of the wide area network port is 64, and the default value of OSPF is 100 divided by the interface bandwidth 1.544 = 64. You can go to the show interface for query. When the router source interface is connected to another network, is to take the COST value of this interface as the path orientation. For example, in R3, S1/0 and S1/1 are not manually specified if S1/0. The default value is 64. Then, the interface S1/0 is not used for the route from R3 to another route.

3. The cost of the router is the smallest through common sense analysis. It should take the 2 route, but it is not. It is found that it is directly thrown to R1 after the R2 is adopted, instead of following the CIDR Block 172.16.255.0, the COST value is 10. When you go to R4, this path is also calculated by SPF.

4. When R3 forwards the data packet to R2, R2 finds that the data packet is sent to other networks.

Therefore, R2 will not forward data packets to other routers in the same region. Because R2 itself is an ABR, he thinks that packets arriving in other regions need to be directly forwarded to the backbone region. And you happen to be connected to the backbone area. Therefore, R2 forwards data packets directly to the R1 router in the backbone area.

For this reason, the routes we view are inconsistent with the paths of the actually forwarded packets.

5. Next let's take a look at the R3-R2-R4, the original COST is: 4, because I defined R2 F0/0 COST as 2, note: this COST is not 1, because Ethernet it will be calculated by the interface, not the smallest COST value of the network segment to stack the path, R3-R4, we change the f0/0 cost value of R2 to 3. In this case, both are 5. After the change.

Let's take a look at show ip route and find that there are two paths of Server Load balancer in 192.168.1.0.

As a link status routing protocol, OSPF transmits the link status broadcast data LSA to all routers in a region, which is different from the distance vector routing protocol, A router running the distance vector routing protocol Transmits some or all route tables to its adjacent routers.