What should be noted in the interconnection of optical interfaces of mid-low end routers?
1. If the optical interface is not UP, measure the optical power and make sure if it is in the normal range.
2. Test the connection through the software loopback and the physical loopback. For the single-mode module, add an optical attenuator for the test.
3. If the interface is not up after using the methods above, use the force-link command to configure the parameters of GE interface(by default, the interface works in auto-negotiation mode. The interface of devices of other companies is configured manually. When both ends work in different modes, the interface in auto-negotiation mode is down, and the interface with manual setting is up. Both interfaces will be up simultaneously if they work in the same mode).