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Knowledge Base

The Improper Value Causes the OSPF Route Selection to Be Incorrect

Publication Date:  2012-07-17  |   Views:  464  |   Downloads:  0  |   Author:  xwx00004807  |   Document ID:  EKB1000001570


Issue Description

The original network consists of two egress routers and two core switches for OSPF. After the USG9100 is connected to the network and OSPF is enabled, it is discovered that the OSPF route selection is incorrect, which does not comply with the expected result.

Alarm Information


Handling Process

Modify the OSPF value on the interface of the switch to 1. The network restores to normal.

Root Cause

The adjustment of the OSPF route subjects to various factors. The route path can also be changed by manual adjustment of the OSPF cost value. Based on the preceding method, the OSPF cost value is adjusted on the firewall. The route path does not change, even if the cost value increases from 10 to 50 and then 100. In a few seconds after the cost value is adjusted, the network is normal and the route selection complies with the expected result. However, after a few seconds, the network restores to the previous status.
Therefore, there may be a blocking path on the network of the device. After carefully checking the network devices that participate in OSPF neighbor relationship, on the link where the two core switches are connected, we discover that the OSPF cost value on the interface of one core switch is 65,530, causing the link blocked.


When bringing a new device, carefully check the configurations of original devices and analyze the impact on the new network.