NOTE Frame Relay is a Layer 2 protocol that provides connectionless delivery between devices.

Frame Relay, although not listed in the official blueprint for the CCIE Security written exam, has a few terms you should be aware of for the exam:

•Forward explicit congestion notification (FECN)—A bit set by a Frame Relay network to inform DTE receiving the frame that congestion was experienced in the path from source to destination. DTE receiving frames with the FECN bit set can request that higher-level protocols take flow-control action, as appropriate.

•Backward explicit congestion notification (BECN)—A bit set by a Frame Relay network in frames traveling in the opposite direction of frames encountering a congested path. DTE receiving frames with the BECN bit set can request that higher-level protocols take flow-control action, as appropriate. The ISP or WAN switches typically set FECN/BECN.

•Data-link connection identifier (DLCI)—A value that specifies a PVC or SVC in a Frame Relay network. DLCIs are locally significant. Globally significant DLCIs are used for LMI communication between Frame Relay switches.

IP Multicast

This section briefly covers the IP multicast areas of interest for the CCIE written test.

The multicasting protocol was designed to reduce the high bandwidth requirements of technologies, such as video on demand, to a single stream of information to more than one device. Applications include electronic learning, company share meetings (video on demand), and software distribution.

Multicasting can be defined as unicast (one to one), multicast (one to many), and broadcast (one to all).

Multicasting transmits IP packets from a single source to multiple destinations. The network copies single packets, which are sent to a subset of network devices. In IPv4, the Class D addresses ranging from 224.0.0.0 to 239.255.255.255 are reserved for multicast. Routing protocols, for example, use multicasting to send hello packets and establish neighbor adjacencies.

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Table 2-16 displays some common multicast addresses and their uses.

Table 2-16 Class D Multicast Address Examples

224.0.0.10All EIGRP-enabled routers

Asynchronous Communications and Access Devices

An asynchronous (async) communication is a digital signal that is transmitted without precise clocking. The RS-232 session between a router and PC through the console connection is an example of async communications. Such signals generally have different frequencies and phase relationships. Asynchronous transmissions usually encapsulate individual characters in control bits (called start and stop bits) that designate the beginning and the end of each character.

For example, the auxiliary port on Cisco routers can be used to connect a modem and allow out of band (not via the network) management.

The Cisco AS5300 is an example of a device that supports both synchronous and async communication, such as voice, digital, and modem-based traffic (via a Public Switch Telephone Network [PSTN]).

The AS5300, or universal Access Server (AS), is a versatile data communications platform that provides the functions of an access server, router, and digital modem in a single modular chassis. The access server is intended for ISPs, telecommunications carriers, and other service providers that offer managed Internet connections. The AS5300 provides both digital (for example, ISDN) and analog access (dialup users using PSTN) to users on a network.

Figure 2-20 displays a typical scenario where clients, such as Internet dialup users with ISDN and analog phone lines (PSTN), can connect to the Internet using PPP.

Clients are supplied one number to call, and the AS5300 makes intelligent decisions based on the incoming call type, whether it be digital (ISDN) or analog (PSTN).

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Example 2-21 SGBP Configuration Example

Hostname AS1

!

username CCIE password CCIE sgbp group CCIE

sgbp member AS2 1.1.1.2 sgbp member AS3 1.1.1.3 sgbp member AS4 1.1.1.4

The following list explains the IOS commands used in Example 2-21.

•username CCIE password CCIE—Defines the username and password used for authenticating SGBP members. If the password is wrong, an error such as the following is presented on the console:

%SGBP-1-AUTHFAILED: Member [chars] failed authentication

•sgbp group CCIE—Defines a named stack group and makes this router a member of that stack group. Use the sgbp group command in global configuration mode. To remove the definition, use the no form of this command.

•sgbp member ip-address—Specifies the host name and IP address of a router or access server that is a peer member of a stack group. Use the sgbp member command in global configuration mode.