HDLC and PPP are considered to be in layer 2 of the OSI model. There are some differences between which will be describe in this post, If you would like to learn more about at least the basic configuration of PPP including PAP and CHAP check out the post I wrote about year ago. (Basic PPP Configuration) HDLC was first developed by the ISO Cisco tweaked the protocol sometimes called cHDLC and because of this it only works with Cisco equipment. PPP is defined by RFC 1968 which is an open standard and is able to work on multi-vender equipment. Continue reading