Internet Protocols Control Protocols ( IPCP) The internet protocols control protocols establishes configures and terminates the TCP/ IP network protocols layer in a PPP connection. The IPCP packet format inside a PPP frame appears in PPP frames with PCP packets are subject to PPP frame structure modification negotiated during the PPP connection establishing stage. IPCP fields including ID, length and IPCP data are all similar to the corresponding LCP.
figure IPCP packet encapsulated in PPP frame
IPCP packets include an 8 bit code to distinguish among different IPCP messages. Table 3 lists the legal values for he code field and their meanings. These codes are analogous to the ones used by LCP. But do not be misled by the similarity. Although IPCP appears similar to LCP it has nothing to do with LCP responsibilities IPCP in only for establishing TCP/ IP network layer specific option .
A PPP endpoint can send the first IPCP configure request packet after a PPP connection reaches the network state. If a peer respond with an LCP protocols reject, TCP/ IP transport isn't available. Otherwise negotiations continue in a manner similar to LCP and ICP may or may not succeed in configuring TCP/IP. PPP endpoints can also continue to negotiate other networking protocols regardless of the status of TCP/ IP.IPCP packets may be categorized into three types again like LCP. These are configuration termination and errors. There is one error code reject. An IPCP code reject references an earlier IPCP configure request message but otherwise operates identically to the LCP conditions. The followings section describe the remaining IPCP types.
A PPP endpoint sends an IPCP configure request packets with the desired TCP/IP options to its peer and a wait a reply. If the reply is an IPCP configure reject or configure nak this PPP endpoint must send another configure request message with options modifications. This IPCP iterative procedure is identical to both PPP endpoints must send an IPCP configure request to its peer since TCP/ IP options are independent for each direction of a PPP connections.IPCP packets carry their own distinct set of TCP / IP options in the TPCP packet data filed. The IPCP configure all carry these options encoding uses the same format as LCP packets IPCP negotiates all TCP/ IP options simultaneously. Currently the only standard TCP/IP options are for setting IP addresses and IP compression.
When a IPCP configure request sender includes the IP compression protocol option, the sender is requesting to receive TCP/IP packets in compressed form. However the IP address options is the desired local address of the configure request sender. IP addresses a a 32 bits number for a PPP connection endpoint.IPXCP is used to enable configure and disable IPX protocols modules at each end of the link . although multiple versions of the NCP are available. IPCXP is the most common and is overtaking the other IPX- NCPs in popularity.