How Do The Configuration Packets Of Link Control Protocol Work?

LCP or the Link Control Protocol is one of the protocols of point to point protocol (PPP) stack. Configuration packets are used to negotiate the options between the two ends. Four different packets are used for this reason. These are configure-request, configure-ack, configure-nak and the configure-reject packets.

The end point that wishes to start a connection sends the configure-request message with a list of zero or more options to the other end point. It is to be noted that all these options are negotiated in one packet. If all the options listed is the configure request packet are accepted by the receiving end, it then sends the configure-ack packet, that repeats all the options that are requested.

If the receiver of the configure-request packet recognizes all the options but finds that some needs to be omitted or revised (values must be changed), it sends a configure-nak packet to the sender. The sender than omits or revises the options and send a new configure-request packet again. If some of the options are not recognized by the receiving party, it responds with a configure-reject packet, marking all those options that are not recognized. The sender of the request must revise the configure-request message and send a totally new request.