To verify PPP configuration, the “ show interface serial ”, “ show interfaces” and “ debug ppp” commands are mostly used. NOTE: the quality and multilink commands are not frequently used, and they may not work on Packet tracer simulator. The command for configuring multilink PPP is: “ ppp multilink” in the interface configuration mode as shown below for R1 and R2. This in effect allows for load balancing. Multilink PPP is a way to use many physical WAN links with PPP. This will ensure that the link meets this threshold for PPP to work. To implement link quality percentage as a requirement for PPP establishment, we use the command: “ ppp quality ” in the interface configuration mode, this is shown below for our scenario.
The link quality is usually maintained by a parameter called LQM (Link Quality Monitoring) which uses a time lag to make sure that the line does not fluctuate. When the link does not meet the specified quality, PPP does not activate the link. The link quality percentage configuration parameter is used to set the baseline quality percentage. In our scenario, all we need to do is to enter this command on the serial interfaces of R1 and R2 as shown below.Īs we mentioned earlier, the quality of a link is crucial to PPP. The command shown above does not have any other options, however, to use PPP, you must have a layer 3 protocol. This command should be entered in the serial interface of the routers as shown below. The main command used to enable PPP is: “ encapsulation ppp” command. NOTE: the routers you will use should have serial interfaces.
The lab requires that we configure basic PPP and successful completion of the lab will be determined by the verification commands we learnt earlier. The routers have been correctly configured and our task is only to configure the PPP options on the serial links. In our lab, all the options for the PCs as well as the interfaces connecting to the routers from the PCs are configured. The figure below shows the topology that we will be using in the configuration of PPP. Now that we have learnt the workings of PPP, we can go ahead and configure it. The second step is usually optional and it is where LCP tests the link to ascertain whether it has the needed quality to support the various layer 3 protocols.įinally, NCP is used to configure the layer 3 protocols that are in use. This is completed when acknowledgment frames are sent. When establishing a PPP session, LCP negotiates the PPP configuration options at either point of the link. NCPs are protocols that allow PPP to use different layer 3 protocols such as IP, IPX and Apple Talk. LCP is also used to negotiate encapsulation parameters and other PPP configuration options such as authentication, error detection and compression when the link has been established. Determining transmission of different packet sizes.LCP configures the link in the ways listed below: It also negotiates other WAN options that are handled by the NCPs. LCP works on top of layer 1 and it works by establishing, testing and configuring the physical connection. This is the main protocol that PPP uses for its operation. NCP (Network Control Protocols) to negotiate the different layer 3 protocols.LCP (Link Control Protocol) for establishment, configuration and testing of the link.Encapsulation of frames using HDLC protocol.PPP operation is made using three parameters: When PPP detects too many errors on a link, the link is shut down. Link quality management which is a way to monitor the quality of a link in PPP.Some of the features that it offers which are not available in HDLC include: it offers many more features as compared to HDLC and it is an open standard. PPP is a WAN protocol that works at layer 2 by encapsulating frames for transmission over a variety of physical links such as serial cables, cell phones, fiber optic cable among others.
In this chapter, we will look at PPP, we will discuss some of its concepts, learn how to configure PPP as well as its authentication options and finally we will look at verification and troubleshooting of PPP. In the previous chapter, we discussed serial connections in the WAN, we also discussed the default data link encapsulation on CISCO switches which is HDLC.