Cisco Networking Academy Program

Semester 4Module 2

Async Communication

Connecting a Modem To a Router• AUX (Auxiliary): To connect a modem to a Cisco router's AUX port,

you typically use a rollover cable and a RJ-45-to-DB-25 male DCE modem adapter

• Console: Modems are rarely connected to them. This is because the console port does not support hardware flow control. The Request to Send (RTS) and Clear to Send (CTS) pins are not supported

Connecting a Modem To a Router

• Connecting to a serial interface:– physical-layer async

interface command• The Picture shows a

connection between a Cisco 2620 series router and an external modem using an EIA/TIA-232 Smart Serial cable.

Connecting a Modem To a Router

• Connecting a modem to an Access Server Async Lines– Cisco Systems applies

the term "access server" only to devices built especially as concentration points for dial-in and dial-out calls.

68 Pin Async Port

Connecting a Modem to a PC• You can Connect an

external modem using a rollover cable and and RJ-45-to-DB-25 male DCE adapter, which is attached to the modem. One end of the rollover cable connects to the DB-25 adapter on the modem. The other end of the rollover cable connects to a 9-pin serial port on the PC (also called a COM port).

Connecting to the Modem-Reverse Telnet

• Some modems can be configured by using a panel on the unit; however, most modems don't have configuration panels.

• Instead, you must access the modem's software via another device such as an access server. When using a Cisco access server, you have the option to manually configure the modem or automatically configure the modem using a script.

• Manual configurations are accomplished using a technique called reverse Telnet.

Connecting to the Modem-Reverse Telnet

Connecting to the Modem-Reverse Telnet

• When using reverse Telnet, you can use the telnet command to connect to any IP address configured on the router, as long as the interface associated with that IP address is up.

• Typically, you configure the access server with a loopback IP address. Since a loopback interface is a logical interface, it is not susceptible to physical failures.

Lines Type and Numbering• Different router models number the line types in different

ways. The figure shows the Cisco line-numbering rules, where n represents the first physical line after the console line, and m refers to the number of the vty line

• For example, the VTY 4 line corresponds to line 14 on a router with eight TTY ports. Because line 0 is for the console, lines 1 to 8 are the TTY lines, line 9 is for the auxiliary port, and lines 10 to 14 are for VTY 0 to 4.

Lines Type and Numbering• Reverse Telnet connections to an individual line can be

used to communicate and configure an attached device. • To connect to an individual line, the remote host or

terminal must specify a particular TCP port on the access server.

• For reverse Telnet, that port is 2000 plus the line number. For example: telnet 131.108.30.40 2001:– This command indicates a Reveres Telnet connection to line 1

(2000 + 1). – If you want to reverse Telnet to a modem on line 14, you would

use TCP port 2014.

Lines Type and Numbering

Configuring Reverse Telnet• RTA#configure terminalRTA(config)#line 10RTA(config-line)#transport input allRTA(config-line)#modem inout

• Transport input all allows all of the following protocols to be used for the connection: LAT, MOP, NASI, PAD, rlogin, Telnet, and v120. Each of these protocols can be specified individually as a command option

• The modem inout command is required to permit both incoming and outgoing connections on a given line.

Configuring Reverse Telnet

Basic Terminal Line Configuration

Most AUX ports are limited to 38400 bps, although AUX ports on 2600 and 3600 series routers support speeds up to 115200 bps.