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Cisco IOS Release 12.0 Dial Solutions Configuration Guide
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About This Manual
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Using Cisco IOS Software
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Overview of Interfaces, Controllers, and Lines Used for Dial Ac
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Configuring Modem Support and Other Asynchronous Devices
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Managing Modems
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Configuring Terminal Operating Characteristics for Dial-In Sess
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Setting Up ISDN Basic Rate Service
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Configuring Synchronous Serial Ports
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Configuring Channelized E1 & T1
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Configuring ISDN Special Signaling
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Configuring Dial-In Terminal Services
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Configuring Protocol Translation & Virtual Asynchronous Devices
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Configuring the Cisco PAD
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Configuring Media-Independent PPP & Multilink PPP
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Configuring Asynchronous PPP and SLIP
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Configuring V.120 Access
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Configuring AppleTalk Remote Access
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Deciding and Preparing to Configure DDR
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Preparing for Asynchronous DDR
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Configuring Legacy DDR Spokes
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Configuring Legacy DDR Hubs
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Configuring Peer-to-Peer DDR with Dialer Profiles
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Configuring DialOut
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Configuring Dial Backup for Dialer Profiles
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Configuring Dial Backup Using Dialer Watch
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Establishing a Reverse Telnet Session to a Modem
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Configure Support for NASI Clients to Access Network Resources
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Configuring Virtual Template Interfaces
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Configuring Multichassis Multilink PPP
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Configuring Virtual Profiles
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Per-User Configuration
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Configuring the Bandwidth Allocation Control Protocol
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Configuring PPP Callback for DDR
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Configuring Asynchronous Callback
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Configuring ISDN Caller ID Callback
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Configuring Snapshot Routing
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Configuring Virtual Private Dialup Networks
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Configuring X.25 on ISDN
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Configuring X.25 on ISDN Using AO/DI
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Configuring Easy IP
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Dial Networking Business Applications
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Telco and ISP Dial Scenarios and Configurations
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Enterprise Dial Scenarios & Configurations
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Table Of Contents
Configuring Dial-In Terminal Services
Configure Telnet and UNIX Rlogin
Make Telnet and UNIX Rlogin Connections
Use UNIX Style Syntax for Rlogin Connections
LAT Sessions and Connection Support
VMS Version 5.4 or Earlier System
VMS Version 5.5 or Later System
Port Names When Configuring a LAT Printer
Control Service Announcements and Service Solicitation
Enable Remote LAT Modification
Monitor and Maintain LAT Connections
Establishing Basic LAT Service Example
Establishing a LAT Service with Selected Group Codes Example
Displaying the LAT Services on the Same LAN Example
Establishing an Outbound LAT Session Example
Logically Partitioning LAT Services by the Terminal Line Example
Configuring LAT Rotary Groups Example
Associating a Rotary Group with a Service Example
Use the Default Terminal Emulation File to Connect
Copy a Sample Terminal Emulation File
Custom Terminal Emulation File Example
Custom Keyboard Emulation File Example
Line Specification for a Custom Emulation Example
Select Fonts for X Terminal Applications
Standard XRemote Configuration Example
Connect through Automatic Session Startup with XDMCP Server Example
Connect through Automatic Session Startup with DECwindows Login via LAT Example
Enable XRemote Manually Example
Connect an X Display Terminal Example
Make XRemote Connections between Servers Example
Configuring Dial-In Terminal Services
This chapter describes how to configure support for asynchronous character stream calls running Telnet, rlogin, local-area transport (LAT), XRemote, or TN3270 and includes the following sections:
Inbound asynchronous character stream calls are routed to virtual terminal lines and virtual asynchronous interfaces, which are used to terminate incoming character steams that do not share a physical connection with the access server or router (such as a physical interface). A virtual asynchronous interface is the place where inbound Telnet, LAT, V.120, TN3270, and PAD calls or sessions terminate on the router. Virtual terminal lines are used for attaching to the router in a nonphysical way.
For a complete description of the dial-in terminal services commands in this chapter, refer to the Dial Solutions Command Reference. To locate documentation of other commands that appear in this chapter, use the command reference master index or search online.
Overview
Configuring support for terminal service connections means to enable network devices running the same protocol (such as LAT or TCP) to connect across a LAN or WAN through network and terminal-emulation software such as Telnet, rlogin, TN3270, LAT, and NetWare Asynchronous Services Interface (NASI).
Terminal Services
Terminal services permit asynchronous devices to be connected to a LAN or WAN through network and terminal-emulation software including Telnet, rlogin, NASI, Digital's LAT protocol, and IBM TN3270. (See .)
Access services permit terminals to connect with remote hosts using virtual terminal protocols including Telnet, NASI, LAT, TN3270, rlogin, and X.25 packet assembler/disassembler (PAD). You can use a router that supports access services to function as a terminal server to provide terminal access to devices on the network.
A host can also connect directly to an access server. In IBM environments, TN3270 allows a standard ASCII terminal to emulate a 3278 terminal and access an IBM host across an IP network.
In Digital environments, LAT support provides a terminal with connections to VMS hosts. X.25 PAD allows terminals to connect directly to an X.25 host over an X.25 network through the router. X.25 PAD eliminates the need for a separate PAD device. This connection requires use of one of the synchronous serial interfaces on the router supporting access services.
shows some of the terminal connection services available on your router.
Figure 238 Terminal Connection Services
Supported Protocols
The following protocols are supported for dial-in terminal services:
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Telnet and rlogin—Of all protocol suites, Transmission Control Protocol/Internet Protocol (TCP/IP) is the most widely implemented on networks of all media types. TCP/IP is today's standard for internetworking and is supported by most computer vendors, including all UNIX-based workstation manufacturers. TCP/IP includes Telnet and rlogin.
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Configure Telnet and Rlogin
This section describes how to configure access server and router lines to support Telnet and rlogin connections and includes the following sections:
Cisco's Implementation
Telnet and rlogin are protocols that enable TCP/IP connections to a host. Telnet, a virtual terminal protocol that is part of the TCP/IP protocol suite, is the more widely used protocol. The rlogin protocol is a remote login service developed for the BSD UNIX system. It provides better control and output suppression than Telnet, but can only be used when the host (typically, a UNIX system) supports rlogin. The Cisco IOS implementation of rlogin does not subscribe to the rlogin "trusted host" model. That is, a user cannot automatically log on to a UNIX system from the router, but must provide a user ID and a password for each connection.
Telnet allows a user at one site to establish a TCP connection to a login server at another site, then passes the keystrokes from one system to the other. Telnet can accept either an IP address or a domain name as the remote system address. In short, Telnet offers three main services:
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The Cisco Systems implementation of Telnet supports the following Telnet options:
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Configuration Task List
The following optional configuration tasks are provided:
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Configure Telnet and UNIX Rlogin
To configure support for Telnet or rlogin calls, use the following commands. Unless specified otherwise, all commands are entered in line configuration mode:
The telnet speed command sets the line speed to match line speeds on remote systems in reverse Telnet, host machines hooked to an access server or router to access the network, or a group of console lines hooked up to the access server or router when disparate line speeds are in use at the local and remote ends of the connection. Line speed negotiation adheres to the Remote Flow Control option, defined in RFC 1080.
When the telnet refuse-negotiations command is set, it suppresses negotiation of the Telnet Remote Echo and Suppress Go Ahead options.
The telnet transparent command is useful for coping with different interpretations of end-of-line handling in the Telnet protocol specification.
The telnet sync-on-break command sets the line to cause a reverse Telnet line to send a Telnet Synchronize signal when it receives a Telnet Break signal. The Telnet Synchronize signal clears the data path, but still interprets incoming commands.
Issue the telnet break-on-ip command to control the translation of Telnet Interrupt-Process commands into X.25 Break indications, and to work around the following situations:
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When used with a correctly operating host, Cisco IOS software implements the Telnet Synchronize and Abort Output signals, which can stop output within one packet's worth of data from the time the user types the interrupt character. Issue the ip tcp chunk-size command to configure a faster response to user interrupt characters. Changing the number of characters output, or chunk size, affects neither the size of the packet used nor the TCP window size, either of which would cause serious efficiency problems for the remote host as well as for the access server or router. Instead, the Telnet status is checked after the number of characters specified, causing only a relatively minor performance loss.
Use the ip alias command to configure connections to an IP address to act identically to connections made to the server's primary IP address on the TCP port. A user trying to connect is connected to the first free line in a rotary group using the Telnet protocol.
With the login-string commands options, you can set a pause, prevent a user from issuing commands during a pause, send a Break character, and use a percent sign (%) in the login string. The busy-message command and login-string command are only useful with two-step protocol translation sessions. For more information about protocol translation, refer to the "Configuring Protocol Translation" chapter.
For actual sample configurations on how to configure Telnet and rlogin, see the section "Examples" later in this chapter.
Make Telnet and UNIX Rlogin Connections
Telnet and rlogin are protocols that enable TCP/IP connections to a host.
Telnet, a virtual terminal protocol that is part of the TCP/IP protocol suite, is the more widely used protocol.
The rlogin protocol is a remote login service developed for the BSD UNIX system. It provides better control and output suppression than Telnet, but can only be used when the host (typically, a UNIX system) supports rlogin. The Cisco IOS implementation of rlogin does not subscribe to the rlogin "trusted host" model. That is, a user cannot automatically log on to a UNIX system from the router, but must provide a user ID and a password for each connection.
To provide Telnet and rlogin connection capabilities, use the following commands in EXEC mode:
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connect host [port] [keyword]
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telnet host [port] [keyword]
Log on to a host that supports Telnet.
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show hosts
Display a list of available hosts.
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show tcp
Display the status of all TCP connections.
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Ctrl^
Log off the host by entering the default escape sequence.1
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Choose from the following list of escape sequences, according to your task:
Use Ctrl^ b if your task is to break
Use Ctrl^ c if your task is to interrupt a process (IP)
Use Ctrl^ h if your task is to erase a character (EC)
Use Ctrl^ o if your task is to abort an output display (AO)
Use Ctrl^ t if your task is to confirm you are at the host (AYT)
Use Ctrl^ u if your task is to erase a line (EL)
Log off the host by entering a special escape sequence.1 These special Telnet sequences map generic terminal control functions to operating system-specific functions.
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Ctrl-^ ?
List the available Telnet commands at any time during the active Telnet session.1
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rlogin host [-l username]
[/user username] [debug]Log on to a host that supports rlogin.
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exit
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logout
Exit a Telnet or rlogin session.
1 Press and hold the Ctrl and Shift keys while pressing the 6 key. You can enter the command character as you hold down Ctrl or with Ctrl released; you can enter the command characters as either uppercase or lowercase letters.
With the Cisco IOS implementation of TCP/IP, you are not required to enter the connect or telnet commands to establish a Telnet connection. You can just enter the learned host name—as long as the host name is different from a command word for the router. Telnet must be the default (you can make it the default with the transport preferred command. Use the show hosts EXEC command to display a list of the available hosts. Use the show tcp EXEC command to display the status of all TCP connections. The Cisco IOS software assigns a logical name to each connection, and several commands use these names to identify connections. The logical name is the same as the host name, unless that name is already in use, or you change the connection name with the name-connection EXEC command. If the name is already in use, the Cisco IOS software assigns a null name to the connection. For an example of making a Telnet connection, see the "Examples" section later in this chapter.
After the rlogin command is issued, you can have several concurrent rlogin connections open and switch between them. To open a new connection, exit the current connection by entering the escape sequence (Ctrl-Shift-6 then x [Ctrl^x] by default) to return to the system command prompt, then open a new connection. For an example of making a rlogin connection or switching between connections, see the sections "rlogin Example" or "Switch between Telnet and rlogin Sessions Examples" later this chapter.
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Use UNIX Style Syntax for Rlogin Connections
The rlogin command supports the standard Berkeley Software Distribution (BSD) UNIX -l option. Before this addition was introduced, the rlogin command allowed remote users to log in using the /user username option, which was not compatible with the standard UNIX rlogin -l username option.
This feature is supported on all of Cisco's TCP/IP-enabled routers and access servers.
To set up this UNIX feature, use the following commands beginning in EXEC mode:
Monitor TCP/IP Connections
To display the status of a TCP connection or view a summary of the TCP connection end points in the system, use the following commands in user EXEC mode:
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show tcp [line-number]
Display the status of a TCP connection.
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show tcp brief [all]
Display a summary of the TCP connection end points in the system.
Examples
The following examples are provided:
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Telnet Connection Examples
The following example routes packets from the source system host1 to kl.sri.com, then to 10.1.0.11, and finally back to host1:
router> connect host1 /route:kl.sri.com 10.1.0.11 host1The following example connects to a host with logical name host1:
router> host1Rlogin Example
The following example makes an rlogin connection to a host at address 108.33.21.2 and enables the message mode for debugging:
router> rlogin 108.33.21.2 debugRlogin UNIX Style Syntax Example
The following example illustrates how the user, Joe Smith, can use rlogin ? (help) and debug to establish and troubleshoot a remote connection to the host Alviso:
4500> rlogin ?WORD IP address or hostname of a remote system4500> rlogin Alviso ?-l Specify remote username/user Specify remote usernamedebug Enable rlogin debugging output<cr>4500> rlogin Alviso -l ?WORD Remote user name4500> rlogin Alviso -l jsmith ?debug Enable rlogin debugging output<cr>4500> rlogin Alviso -l jsmith debugSwitch between Telnet and rlogin Sessions Examples
You can switch between sessions by escaping one session and resuming a previously opened session. The following example shows how to escape out of a connection to the host host1 and to resume connection 2. You escape out of the current session and return to the EXEC prompt by entering the command sequence Ctrl-Shift-6 then x. Resume the connection with the resume [connection] [keyword] command.
host1% ^^Xrouter> resume 2You can omit the command name and simply enter the connection number to resume that connection. The following example illustrates how to resume connection 3:
router> 3To list all the open sessions associated with the current terminal line, use the where command.
List Supported Telnet Commands Example
At any time during an active Telnet session, you can list the Telnet commands by pressing the escape sequence keys (by default Ctrl-Shift-6) followed by a question mark at the system prompt:
Ctrl-^ ?
A sample of this list follows:
router> ^^?
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[Special telnet escape help]^^B sends telnet BREAK^^C sends telnet IP^^H sends telnet EC^^O sends telnet AO^^T sends telnet AYT^^U sends telnet ELConfigure LAT
The Digital Equipment Corporation (Digital) Local Area Transport (LAT) protocol is the one used most often to connect to Digital hosts. LAT is a Digital-proprietary protocol. We provide LAT technology licensed from Digital. This section describes how to configure the LAT transmission protocol.
The following sections are provided:
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Cisco's Implementation
The LAT protocol allows a user to establish a LAT connection to a host at another site, then pass the keystrokes from one system to the other. A user can establish a LAT connection through a router to a LAT host simply by entering the host name. The Cisco IOS software supports the LAT 5.2 specification.
Unlike the Transmission Control Protocol/Internet Protocol (TCP/IP), LAT was designed to be used on LANs and it cannot be routed because it does not have a routing layer. However, a bridge or combined bridge and router, such as a Cisco router, can be used to carry LAT traffic across a WAN. Protocol translation can be used to carry LAT traffic over a WAN by first translating LAT to X.25 or Telnet, as shown in .
Figure 239 Comparing LAT and TCP/IP Protocol Stacks
The following sections describe Cisco's implementation of LAT in more detail:
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LAT Functionality
The LAT protocol is asymmetrical; it has master and slave functionality. First, the LAT master starts a LAT circuit by sending a circuit start message, and then a LAT slave responds with its own circuit start message. From 1 to 255 LAT sessions can then be multiplexed on a circuit.
In a typical setup, where the user's terminal is connected to a router, the router acts as the master, and the target VMS host acts as the slave.
For example, the following command results in the device router1 acting as the master (or server) and the target VMS host, wheel, acting as the slave (or host).
router1> lat wheelA router can also act as a slave. This happens if the user connects from one access server to another. For example, the following command results in router1 acting as the master (server) and router2 acting as the slave (host).
router1> lat router2In a LAT host-initiated connection, the VMS system always acts as the LAT slave. For example, a print job originating from a VMS system initiates or triggers the router to which the printer is connected to act as the LAT master. In short, the master-slave relationship also applies to host-initiated sessions from a LAT slave.
LAT Services
Resources such as modems, computers, and application software are viewed in a LAT network as services that, potentially, any user in the network can use. A LAT node can offer one or more such LAT services, and more than one LAT node can offer the same LAT service.
A LAT node that offers one or more services, collectively called advertised services, broadcasts its services in the form of Ethernet multicast messages, called LAT service announcements. Conversely, a LAT node can listen for LAT service announcements on the network. These messages are cached in a dynamic table of known LAT services, collectively called learned services.
The Cisco IOS software supports both learned and advertised LAT services; therefore, it also supports incoming and outgoing LAT sessions. The services rating of its advertised nodes are determined dynamically but can also be set statically.
To establish outgoing connections to a LAT service, the Cisco IOS software searches for the service in the learned services cache. If one or more nodes is offering the same service, the node with the highest rating is chosen. For example, a LAT connection to a service offered by a VAX cluster connects to the node in that cluster with the smallest load and thus the highest service rating. This is how load balancing works in relation to a group of nodes offering the same service.
To establish an incoming connection, a LAT session connects from another LAT node to the service advertised by the local LAT node.
LAT Groups
Because potentially any user can access any of the services on a LAT network, a LAT server manager uses the concept of group codes to allow or restrict access to the services.
When both the router and the LAT host share a common group code, a connection can be established between the two. If the default group codes have not been changed on either side, a user on any router can connect to any learned service on the network.
However, if you define groups for access servers or routers and LAT hosts, you can partition these services into logical subnetworks. You can organize the groups so that users on one device view one set of services, and users on another device (or another line on the same device) view a different set. You might also design a plan that correlates group numbers with organizational groups, such as departments. The section "Configuration Task List" in this chapter describes how to enter group code lists in your configuration file.
A LAT host node's services cannot be accessed individually; access is granted, per node, on an
all-or-none basis.LAT Sessions and Connection Support
A LAT session is a two-way logical connection between a LAT service and the router. All this is transparent to the user at a console connected to a LAT session; to the user it appears that connection has been made directly to the desired device or application program. There is no inherent upper limit to the number of LAT sessions you can create from an asynchronous terminal to the router.
When a host print job connects to a router, this is called a host-initiated connection. The Cisco IOS software maintains a queue of hosts requesting connection by sending periodic status messages to the requesting host.
You can establish host-initiated connections by specifying a port number or by defining a service. These same services are used for connections from other access servers or routers.
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Connect a VMS Host Using LAT
The process of connecting to a VMS host is slightly different if you are connecting to a VMS host running VMS Version 5.4 or earlier than when connecting to a VMS host running VMS Version 5.5 or later software.
VMS Version 5.4 or Earlier System
If a host-initiated connection is received that specifies a destination port number that corresponds to a virtual port on the router, a virtual EXEC process will be created for the user to log in with. This process can be used, in conjunction with the Digital set host/dte command on VMS, to connect to a router named router1 from a VMS host node, as shown in the following example:
$lcp :==$latcp$lcp create port lta300:$lcp set port lta300:/service=able /node=router1$set host/dte lta300:VMS Version 5.5 or Later System
To connect to a VMS host running VMS Version 5.5 or later, you must turn on the VMS LAT hosts's outgoing connections and use the Digital set host/lat command, as shown in the following example:
$lcp :== $latcp$lcp set node/connection =outgoing$set host/lat ablePort Names When Configuring a LAT Printer
When you configure a LAT printer, the LAT port name is the line number without the "TTY." For example, if you configure terminal line 10, named ABLE, to be a LAT printer port, you must use the OpenVMS command to associate an arbitrary LAT device to a LAT port name as follows:
$lcp :== $lcp$lcp create port lta300:$lcp set port/node=ABLE/port=10 lta300:The LAT port name is the line number without the "TTY," regardless of whether the format of the TTY line number is decimal or octal.
Additional LAT Capability
The Cisco IOS software fully supports the LAT protocol suite, and provides the following features:
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Configuration Task List
The Cisco IOS software LAT protocol is supplied with a default configuration and does not require additional configuration for you to use it. The software does provide commands for customizing the LAT software for your environment, if desired.
Perform the tasks in the following sections to enable LAT and customize LAT for your particular network environment:
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Configure Basic LAT Services
To enable basic LAT services, use the following commands in global configuration mode:
Use the lat out-group command to define the list of services to which a user can connect. Do this by defining the group code lists used for connections from specific lines. You can limit the connection choices for an individual line by defining the group code lists for an outgoing connection. When a user initiates a connection with a LAT host, the user's line must share a common group number with the remote LAT host before a connection can be made.
Use the lat group-list command to specify a name for group lists to simplify the task of entering individual group codes. A name makes it easier to refer to a long list of group code numbers. To display the defined groups, use the show lat groups command.
Use the lat service-group command to specify a group code mask to use when advertising all services for a node. You can enter more than one group code by listing the numbers. You can also enter both a group code name and group codes.
Use the lat remote-modification line configuration command to configure a LAT line so that a remote LAT node can change the operating characteristics of the line.
Enable Inbound Services
Just as LAT services are offered by host computers, they also can be offered by access servers and routers, as they implement both the host and server portions of the LAT protocol. This allows connections from either hosts or local access servers or routers. When a host connects to a local device, this is called a host-initiated connection.
The tasks described in this section define support for host-initiated connections. This support includes refining the list of services that the router will support. An incoming session can be to either a port or a service. The port name is the terminal line number, as reported by the EXEC command show users all. Use the following commands in global configuration mode:
Use the show lat advertised EXEC command to display LAT services offered to other systems on the network.
A service must be specifically enabled, but not all of the attributes in the previous task table are necessary in a particular environment.
Control Service Announcements and Service Solicitation
You can configure the Cisco IOS software to support the service responder feature that is part of the LAT Version 5.2 specification.
Specifically, the DECserver90L+, which has less memory than other DEC servers, does not maintain a cache of learned services. Instead, the DECserver90L+ solicits information about services as they are needed.
LAT Version 5.2 nodes can respond for themselves, but LAT Version 5.1 nodes, for example VMS Version 5.4 or earlier nodes, cannot. Instead, a LAT Version 5.2 node configured as a service responder can respond in proxy for those LAT Version 5.1 nodes.
The Cisco IOS software can be configured as a LAT service responder. Of course, if all your nodes are LAT Version 5.2 nodes, you do not need to enable the service responder features.
To control service announcements and service solicitations, use the following commands in global configuration mode:
Use the lat service-responder command to configure the Cisco IOS software to respond to solicit information requests addressed to LAT Version 5.1 nodes. This function allows nodes that do not cache service advertisements to interoperate with nodes that do not respond to solicit requests. shows how a router can act as a proxy for LAT servers.
Figure 240 Router as Proxy for LAT Server
The DECserver90L+ broadcasts a solicit information request in search of service "Stella's" address. The VMS host, Stella, is unable to respond to the request because it is running LAT Version 5.1. The access server is running LAT Version 5.2 with service responder enabled and informs the DECserver90L+ of Stella's address.
Use the no lat service-announcements command to disable periodic broadcasts of service announcements. If service announcements are enabled, the LAT node will periodically broadcast service advertisements. If service announcements are disabled, the LAT node will not send service announcements, so a remote node requiring connection to the local node has to use solicit-information messages to look up node information. Only disable service announcements if all of the nodes on the LAN support the service responder feature.
Use the lat service-timer command to adjust the time between LAT service advertisements for services offered. This is useful in large networks with many LAT services and limited bandwidth.
Configure Traffic Timers
You can customize the environment for transmitting LAT messages. The Cisco IOS implementation of LAT allows you to set the following features:
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These features affect all LAT connection types. Use the following commands in global configuration mode:
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lat retransmit-limit number
Set the message retransmit limit.
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lat ka-timer seconds
Set the keepalive timer.
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lat vc-timer milliseconds
Set the virtual-circuit timer.
Optimize Performance
To optimize performance for your LAT environment, use one or more of the following commands beginning in global configuration mode:
Use the lat host-buffers command to set the number of messages received by a host at one time. Increasing this number can enhance performance. Before LAT Version 5.2, LAT allowed only one outstanding message at one time on a virtual circuit. This restriction could limit the performance of the Cisco IOS software processing a large number of messages because only one Ethernet packet of data could be in transit at a time. During virtual circuit startup, each side communicates to the other how many outstanding messages it is willing to accept.
Use the lat server-buffers command to set the number of messages received by a server at one time. Increasing this number can enhance performance. Before LAT Version 5.2, LAT allowed only one outstanding message on a virtual circuit at a time. This restriction limited the performance of Cisco IOS software when it processed a large number of messages, because only one Ethernet packet of data could be in transit at a time. With LAT Version 5.2, nodes can indicate that they are willing to receive more than one message at a time. During virtual circuit startup, each side communicates to the other how many outstanding messages it is willing to accept.
Use the lat host-delay command to set a user-defined delay for the acknowledgment for incoming LAT slave connections. This is useful in situations where you need to control the delay. For example, if data is being transferred between a Digital server (using LAT) and a UNIX host (using Telnet) via a protocol translator, the protocol translator imposes the LAT delay on the Telnet as well as the LAT service, where Telnet may timeout due to the LAT restriction.
Define Access Lists
Because LAT groups were not intended to implement security or access control, the Cisco IOS software supports access lists to provide these functions. An access list is a sequential collection of permit and deny conditions that serve to restrict access to or from LAT nodes on a specific terminal line. Each access list statement defines a permit or deny condition and a matching criterion for the node name.
When a LAT connection is attempted (either incoming or outgoing), the node name of the destination service (not the service name) is compared against the regular expression. If they match, the connection is permitted or denied as specified.
Use the following commands to define access lists and conditions:
Enable Remote LAT Modification
You can configure a LAT line so that a remote LAT node can change the operating characteristics of the line. To enable remote LAT modification, use the following command in line configuration mode:
Make LAT Connections
The Digital Equipment Corporation (Digital) LAT protocol is most often used to connect routers to Digital hosts. LAT is a Digital-proprietary protocol, and the Cisco IOS software uses LAT technology licensed from Digital to allow the following LAT services:
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For actual LAT connection examples, see the "LAT Connection Examples" section later in this chapter.
To enable specific LAT connections or services, use the following commands in EXEC mode:
lat name [node nodename | port portname | /debug]
Connect to a LAT host.1
terminal lat out-group {groupname | number | range}
(Optional) Define a temporary list of services to which you or another user can connect by defining the group code lists used for connections from specific lines.
show lat services [service-name]
(Optional) List available LAT services.
help
(Optional) List the subset of Digital commands that the Cisco IOS software supports.
exit
(Optional) Exit a LAT session by logging off the remote system. Then, terminate the active LAT session.
1 You can quit the connection by pressing Ctrl-C or complete the connection by entering the password for a given service.
You can also set your preferred connection protocol to any available connection protocol supported in the Cisco IOS software. Your preferred connection protocol is also referred to in the Cisco IOS software as a "preferred transport type." If your preferred connection protocol is set to lat, you can use the connect command in place of the lat command. To configure a preferred connection protocol, use the transport preferred command. When your preferred connection protocol is set to none or to another protocol, you must use the lat command to connect to a LAT host.
To specify a temporary list of services to which you or another user can connect, you must define the group code lists used for connections from specific lines. You limit the connection choices for an individual line by defining the group code lists for an outgoing connection. To define a group code list, use the terminal lat out-group command. When a user initiates a connection with a LAT host, the user's line must share a common group number with the remote LAT host before a connection can be made. The group code range must be a subset of the line's configured group code range.
You can have several concurrent LAT sessions open and switch between them. To open a subsequent session, first enter the escape sequence (Ctrl-Shift-6 then x [Ctrl^x] by default) to suspend the current session. Then open a new session. To list the available LAT services, issue the show lat services EXEC command.
Monitor and Maintain LAT Connections
To monitor and maintain LAT connections, use the following commands in EXEC mode:
Examples
This section contains the following LAT examples:
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Establishing Basic LAT Service Example
The following example establishes the LAT service ABLE for your router. Subsequently, your router advertises ABLE (with default group code 0) on the LAN. Other LAT nodes can connect to you using LAT service ABLE, provided the group codes on the LAT nodes and the group codes for ABLE intersect. By default, most LAT nodes, such as OpenVMS Version 5.5 hosts, have user group code set to 0, so you have default access to ABLE.
! Create LAT service with password protection and! identification string using the following global configuration commandslat service ABLE password secretlat service ABLE ident Welcome to my machineEstablishing a LAT Service with Selected Group Codes Example
The following example establishes the LAT service ABLE from your router with selected group codes 1, 4 through 7, and 167. This limits inbound access to those LAT nodes that have group codes that intersect with those for LAT service ABLE.
! Establish a LAT group listlat group-list HUBS 1 4-7 167!! Enable LAT group list for the service-grouplat service-group HUBS enabled!! Create LAT service with password protection and! identification stringlat service ABLE password secretlat service ABLE ident Welcome to my machineDisplaying the LAT Services on the Same LAN Example
The following example demonstrates how you can check which LAT services are on the same LAN as your router. Note that your router's own LAT service ABLE is also listed, with the "Interface" column listing the interface as "Local."
able> show lat servicesService Name Rating Interface Node (Address)CAD 16 Ethernet0 WANDERABLE 16 LocalCERTIFY 33 Ethernet0 STELLAEstablishing an Outbound LAT Session Example
The following example establishes a LAT session to remote LAT service HELLO using an interactive session:
able> lat HELLOLogically Partitioning LAT Services by the Terminal Line Example
The following example illustrates how LAT services are logically partitioned by terminal line. At the example site, lines 1 through 7 go to the shop floor, lines 8 through 11 go to the Quality Assurance department, and lines 12 through 16 go to a common area.
! Define LAT groupnameslat group-list DEFAULT 0lat group-list FLOOR 3lat group-
