Config, Monitoring and Dialup

LAT to Telnet is one form of protocol translation used on Cisco access servers.

Exam Objective # 50 Access lists are used to either permit or deny access to the internal or external network based on source IP address, destination IP address, or protocol.

To specify which DHCP server to use on your network use the command: ip dhcp-server ip-address

To display debug traces for the Virtual Private Dialup Network (VPDN) feature, which provides PPP tunnels using the Layer 2 Forwarding (L2F) protocol, use the debug vpdn EXEC command. The no form of this command disables debugging output. [no] debug vpdn {errors | events | packets | l2f-errors | l2f-events | l2f-packets} Syntax Description errors - Displays errors that prevent a tunnel from being established or errors that cause an established tunnel to be closed. events - Displays messages about events that are part of normal tunnel establishment or shutdown. packets - Displays each protocol packet exchanged. This option may result in a large number of debug messages and should generally only be used on a debug chassis with a single active session. l2f-errors - Displays L2F protocol errors that prevent L2F establishment or prevent its normal operation. l2f-events - Displays messages about events that are part of normal tunnels establishment or shutdown for L2F. l2f-packets - Displays messages about L2F protocol headers and status.

VPDN uses the Layer 2 Forwarding protocol (L2F) which permits the tunneling of link level frames. Using L2F tunneling, an Internet Service Provider (ISP) or other access service can create a virtual tunnel to link a customer's remote sites or remote users with corporate home networks. In particular, a network access server at the ISP's point of presence (POP) exchanges PPP messages with the remote users, and communicates by L2F requests and responses with the customer's home gateway to set up tunnels. L2F passes protocol-level packets through the virtual tunnel between endpoints of a point-to-point connection. Frames from the remote users are accepted by the ISP's POP, stripped of any linked framing or transparency bytes, encapsulated in L2F, and forwarded over the appropriate tunnel. The customer's home gateway accepts these L2F frames, strips the L2F encapsulation, and processes the incoming frames for the appropriate interface.

Command Syntax: [ no] debug vpdn {errors | events | packets | l2f-errors | l2f-events | l2f-packets} Syntax Description errors: Displays errors that prevent a tunnel from being established or errors that cause an established tunnel to be closed. events: Displays messages about events that are part of normal tunnel establishment or shutdown. packets: Displays each protocol packet exchanged. This option may result in a large number of debug messages and should generally only be used on a debug chassis with a single active session. l2f-errors: Displays L2F protocol errors that prevent L2F establishment or prevent its normal operation. l2f-events: Displays messages about events that are part of normal tunnels establishment or shutdown for L2F. l2f-packets: Displays messages about L2F protocol headers and status.

A signal from a device indicating that it is ready to communicate with an external device. RTS: Ready to Send/Request to Send. RS-232 signal that requests to send data over a line. CTS: Clear To Send. Hardware flow-control on a control port or data port. DTR: Data Terminal Ready. Hardware flow-control.

To tunnel SLIP or PPP across an X.25 WAN to an IP network using the two-step protocol translation method, use the vty-async command, which enables you to run PPP and SLIP on VTY lines. Normally, PPP and SLIP function only on physical asynchronous interfaces. The vty-async command enables you to run PPP and SLIP on VTY lines, which permits you to tunnel from an incoming protocol to SLIP or PPP and then to an IP network (or IPX-PPP to an IPX network).

A dialer rotary group is useful in environments that require multiple calling destinations. Only the rotary group needs to be configured with dialer map commands.

Dial Backup is used to bring up a line when a circuit goes down, whereas Dial on Demand is used to bring up a circuit whenever interesting traffic is received.

If possible, configure modems using reverse connection. To make a reverse connection, issue this Telnet command from anywhere on the network that can ping x.x.x.x: telnet x.x.x.x 20yy where x.x.x.x is any active, connected, and up interface on the Cisco device and yy is the line number to which you want to connect.

To select a backup interface. backup interface type number or backup interface type slot/port (For the Cisco 7500 series) or backup interface type slot/port-adapter/port (Cisco 7200 series)

You can configure a value that defines how much time should elapse before a secondary line status changes after a primary line status has changed. This means that you can define two delays: A delay that applies after the primary line goes down but before the secondary line is activated A delay that applies after the primary line comes up but before the secondary line is deactivated backup delay {enable-delay | never} {disable-delay | never}

Dialer profiles allow the configuration of physical interfaces to be separated from the logical configuration required for a call, and they also allow the logical and physical configurations to be bound together dynamically on a per-call basis. A dialer profile consists of the following elements:
A dialer interface (a logical entity) configuration including one or more dial strings (each of which is used to reach one destination subnetwork)
A dialer map class that defines all the characteristics for any call to the specified dial string
An ordered dialer pool of physical interfaces to be used by the dialer interface

All calls going to or from the same destination subnetwork use the same dialer profile. A dialer interface configuration includes all settings needed to reach a specific destination subnetwork (and any networks reached through it). Multiple dial strings can be specified for the same dialer interface, each dial string being associated with a different dialer map-class. The dialer map-class defines all the characteristics for any call to the specified dial string.
For example, the map-class for one destination might specify a 56-kbps ISDN speed; the map-class for a different destination might specify a 64-kbps ISDN speed. Each dialer interface uses a dialer pool, a pool of physical interfaces ordered on the basis of the priority assigned to each physical interface. A physical interface can belong to multiple dialer pools, contention being resolved by priority. ISDN BRI and PRI interfaces can set a limit on the minimum and maximum number of B channels reserved by any dialer pools. A channel reserved by a dialer pool remains idle until traffic is directed to the pool. When dialer profiles are used to configure DDR, a physical interface has no configuration settings except encapsulation and the dialer pools the interface belongs to.

All dialer profiles have the following elements: A dialer interface (a logical entity) configuration including one or more dial strings (each of which is used to reach one destination subnetwork) A dialer map class that defines all the characteristics for any call to the specified dial string An ordered dialer pool of physical interfaces to be used by the dialer interface Note: All calls going to or from the same destination subnetwork use the same dialer profile.

The reverse-telnet can be terminated by typing Ctrl-Shift-6 followed by x. This will suspend the session and leave the user at a router prompt. Then to terminate the session enter the disconnect command.

All dialer profiles have the following elements: A dialer interface (a logical entity) configuration including one or more dial strings (each of which is used to reach one destination subnetwork) A dialer map class that defines all the characteristics for any call to the specified dial string An ordered dialer pool of physical interfaces to be used by the dialer interface Note: All calls going to or from the same destination subnetwork use the same dialer profile.

To verify your controller is up and running and no alarms have been reported: Enter the show controller t1 or show controller e1 command and specify the port number: 5300# show controller t1 0 T1 0 is up. No alarms detected. Framing is ESF, Line Code is AMI, Clock Source is Line Primary. Version info of slot 2: HW: 2, Firmware: 14, NEAT PLD: 13, NR Bus PLD: 19 Data in current interval (476 seconds elapsed): 0 Line Code Violations, 0 Path Code Violations 0 Slip Secs, 0 Fr Loss Secs, 0 Line Err Secs, 0 Degraded Mins 0 Errored Secs, 0 Bursty Err Secs, 0 Severely Err Secs, 0 Unavail Secs Total Data (last 24 hours) 0 Line Code Violations, 0 Path Code Violations, 0 Slip Secs, 0 Fr Loss Secs, 0 Line Err Secs, 0 Degraded Mins, 0 Errored Secs, 0 Bursty Err Secs, 0 Severely Err Secs, 0 Unavail Secs.

Full statement: The dialer group number is used with the dialer-list command to determine which packets will be meet the criteria specified by the dialer-list command and activate the ISDN connection.

You can enable PPP on serial lines to encapsulate IP and other network protocol datagrams. To do so, use the following command in interface configuration mode: encapsulation ppp.

If you are having trouble: Make sure the serial interface and protocol are up by entering the show interface serial command.