This read-only field reports the IP address of the client device connected via this ISDN B-channel, tying the underlying ISDN circuit-switched connection to the IP-layer identity of whatever device is using it. An admin uses this to identify exactly which IP-addressed client or router is currently occupying this B-channel, useful for capacity planning or for tracking down which specific device is generating traffic over a dial-up ISDN connection. For example, if an unexpected device shows up as lportISDNIpAddr on a B-channel meant only for a specific branch's backup traffic, that is a sign of an unauthorized or misconfigured dial-in client.