Router(config)#interface bri 0
Router(config-if)#isdn spid1 51055510000001 5551000
Defines the SPID number for channel B1, as assigned by the service provider
The second number (5551000) is the local dial directory number (LDN), which usually matches the information coming from the ISDN switch
Router(config-if)#isdn spid2 51055510010001 5551001
Defines the SPID number for channel B2, as assigned by the service provider
Not all switch types need SPIDs assigned to your router. Your service provider will let you know whether you need to configure SPIDs.