Cisco Systems C819HG4GVK9 Information About Configuring Serial Interfaces, PPP Encapsulation

Chapter 8 Configuring the Serial Interface

Information About Configuring Serial Interfaces

Information About Configuring Serial Interfaces

To configure serial interfaces, you must understand the following concept:

•Cisco HDLC Encapsulation, page 8-3

•PPP Encapsulation, page 8-3

•Keepalive Timer, page 8-4

•Frame Relay Encapsulation, page 8-5

Cisco HDLC Encapsulation

Cisco High-Level Data Link Controller (HDLC) is the Cisco proprietary protocol for sending data over synchronous serial links using HDLC. Cisco HDLC also provides a simple control protocol called Serial Line Address Resolution Protocol (SLARP) to maintain serial link keepalives. Cisco HDLC is the default for data encapsulation at Layer 2 (data link) of the Open System Interconnection (OSI) stack for efficient packet delineation and error control.

Note Cisco HDLC is the default encapsulation type for the serial interfaces.

When the encapsulation on a serial interface is changed from HDLC to any other encapsulation type, the configured serial subinterfaces on the main interface inherit the newly changed encapsulation and they do not get deleted.

Cisco HDLC uses keepalives to monitor the link state, as described in the “Keepalive Timer” section on page 8-4.

PPPEncapsulation

PPPis a standard protocol used to send data over synchronous serial links. PPP also provides a Link Control Protocol (LCP) for negotiating properties of the link. LCP uses echo requests and responses to monitor the continuing availability of the link.

Note When an interface is configured with PPP encapsulation, a link is declared down and full LCP negotiation is re-initiated after five echo request (ECHOREQ) packets are sent without receiving an echo response (ECHOREP).

PPPprovides the following Network Control Protocols (NCPs) for negotiating properties of data protocols that will run on the link:

•IP Control Protocol (IPCP) to negotiate IP properties

•Multiprotocol Label Switching control processor (MPLSCP) to negotiate MPLS properties

•Cisco Discovery Protocol control processor (CDPCP) to negotiate CDP properties

•IPv6CP to negotiate IP Version 6 (IPv6) properties

•Open Systems Interconnection control processor (OSICP) to negotiate OSI properties

Cisco 819 Series Integrated Services Routers Software Configuration Guide

OL-23590-02 8-3