Configuring USB Modems for Dial Backup with a Configuration Editor

To configure USB modem interfaces, perform the following tasks.

Configuring a USB Modem Interface for Dial Backup

To configure a USB modem interface for the device:

  1. Navigate to the top of the interfaces configuration hierarchy.
  2. Perform the configuration tasks described in Table 62.
  3. Go on to Configuring a Dialer Interface for USB Modem Dial Backup.

Table 62: Configuring a USB Modem Interface for Dial Backup

Task

CLI Configuration Editor

Navigate to the Interfaces level in the configuration hierarchy.

From the [edit] hierarchy level, enter

edit interfaces umd0

Create the new interface umd0.

 

Configure dialer options.

Dialer pool priority has a range from 1 to 255, with 1 designating lowest-priority interfaces and 255 designating the highest-priority interfaces.

Enter

set dialer-options pool usb-modem-dialer-pool priority 25

Configure the modem to automatically answer (autoanswer) calls after a specified number of rings.

Note: The default modem initialization string is AT S7=45 S0=0 V1 X4 &C1 E0 Q0 &Q8 %C0. The modem command S0=0 disables the modem from autoanswering calls.

Enter

set modem-options init-command-string "ATS0=2 \n"

Configure the modem to act as a dial-in WAN backup interface.

Enter

set modem-options dialin routable

Configuring a Dialer Interface for USB Modem Dial Backup

The dialer interface (dl) is a logical interface configured to establish USB modem connectivity. You can configure multiple dialer interfaces for different functions on the device.

After configuring the dialer interface, you must configure a backup method—either dialer backup, a dialer filter, or dialer watch.

For example, suppose you have a branch office router and a head office router each with a USB modem interface and a dialer interface. To establish a backup connection between the branch office and head office routers, you can configure them as described in Table 63.

Table 63: Configuring Branch Office and Head Office Routers for USB Modem Backup Connectivity

Router Location

Configuration Requirement

Instructions

Branch Office

  1. Configure the logical dialer interface on the branch office router for USB modem dial backup.
  2. Configure the dialer interface dl0 in one of the following ways on the branch office router:
    • Configure the dialer interface dl0 as the backup interface on the branch office router's primary T1 interface t1-1/0/0.
    • Configure a dialer filter on the branch office router's dialer interface.
    • Configure a dialer watch on the branch office router's dialer interface.

Head Office

Configure dial-in on the dialer interface dl0 on the head office router.

To configure dial-in on the head office router, see Configuring Dial-In for a USB Modem Connection.

To configure a logical dialer interface for USB modem dial backup:

  1. Navigate to the top of the interfaces configuration hierarchy.
  2. Perform the configuration tasks described in Table 64.
  3. To configure a backup method, go on to one of the following tasks:

Table 64: Adding a Dialer Interface for USB Modem Dial Backup

Task

CLI Configuration Editor

Navigate to the Interfaces level in the configuration hierarchy.

From the [edit] hierarchy level, enter

edit interfaces

Create the new interface—for example, dl0.

Adding a description can differentiate between different dialer interfaces—for example, USB-modem-backup.

Create and name the interface:

  1. edit dl0
  2. set description USB-modem-backup

Configure Point-to-Point Protocol (PPP) encapsulation.

Note: You cannot configure Cisco High-Level Data Link Control (HDLC) or Multilink PPP (MLPPP) encapsulation on dialer interfaces used in USB modem connections.

Enter

set encapsulation ppp

Create the logical unit 0.

Note: You can set the logical unit to 0 only.

Enter

set unit 0

Configure dialer options.

  • Activation delay—Number of seconds to wait before activating the backup USB modem interface after the primary interface is down—for example, 30. The default value is 0 seconds, and the maximum value is 60 seconds. Use this option only for dialer backup and dialer watch.
  • Deactivation delay—Number of seconds to wait before deactivating the backup USB modem interface after the primary interface is up—for example, 30. The default value is 0 seconds, and the maximum value is 60 seconds. Use this option only for dialer backup and dialer watch.
  • Idle timeout—Number of seconds a connection is idle before disconnecting—for example, 30. The default value is 120 seconds, and the range is from 0 to 4294967295.
  • Initial route check—Number of seconds to wait before checking if the primary interface is up—for example, 30. The default value is 120 seconds, and the range is from 1 to 300 seconds.
  • Pool—Name of the dialer pool to use for USB modem connectivity—for example, usb-modem-dialer-pool.
  1. Enter

    edit unit 0 dialer-options

  2. Enter

    set activation-delay 60

  3. Enter

    set deactivation-delay 30

  4. Enter

    set idle-timeout 30 initial-route-check 30 pool usb-modem-dialer-pool

Configure the telephone number of the remote destination to call if the primary interface goes down—for example, 5551212.

Enter

set dial-string 5551212

Configure source and destination IP addresses for the dialer interface—for example, 172.20.10.2 and 172.20.10.1.

Note: If you configure multiple dialer interfaces, ensure that the same IP subnet address is not configured on different dialer interfaces. Configuring the same IP subnet address on multiple dialer interfaces can result in inconsistency in the route and packet loss. Packets can be routed through any of the dialer interfaces with the IP subnet address, instead of being routed through the dialer interface to which the USB modem call is mapped.

  1. From the [edit] hierarchy level, enter

    edit interfaces dl0 unit 0

  2. Enter

    set family inet address 172.20.10.2 destination 172.20.10.1

Configuring Dial Backup for a USB Modem Connection

Dial backup allows one or more dialer interfaces to be configured as the backup link for the primary serial interface. The backup dialer interfaces are activated only when the primary interface fails. USB modem backup connectivity is supported on all interfaces except lsq-0/0/0.

To configure a primary interface for backup connectivity:

  1. Navigate to the top of the interfaces configuration hierarchy.
  2. Perform the configuration tasks described in Table 65.
  3. If you are finished configuring the device, commit the configuration.

Table 65: Configuring a Primary Interface for USB Modem Dial Backup

Task

CLI Configuration Editor

Select the physical interface for USB modem USB modem backup connectivity—for example, t1–1/0/0.

From the [edit] hierarchy level, enter

edit interfaces t1-1/0/0 unit 0

Configure the backup dialer interface—for instance, dl0.0.

Enter

set backup-options interface dl0.0

Configuring a Dialer Filter for USB Modem Dial Backup

This dial-on-demand routing backup method allows a USB modem connection to be activated only when network traffic configured as an “interesting packet” arrives on the network. Once the network traffic is sent, an inactivity timer is triggered and the connection is closed.

You define an interesting packet using the dialer filter feature of the device.

To configure dial-on-demand routing backup using a dialer filter, you first configure the dialer filter and then apply the filter to the dialer interface.

To configure the dialer filter and apply it to the dialer interface:

  1. Navigate to the top of the interfaces configuration hierarchy.
  2. Perform the configuration tasks described in Table 66.
  3. Go on to Table 67.
  4. When you are finished configuring the device, commit the configuration.

Table 66: Configuring a Dialer Filter for USB Modem Dial Backup

Task

CLI Configuration Editor

Navigate to the Firewall level in the configuration hierarchy.

From the [edit] hierarchy level, enter

edit firewall

Configure the dialer filter name—for example, interesting-traffic.

  1. Enter

    edit family inet

  2. Then enter

    edit dialer-filter interesting-traffic

Configure the dialer filter rule name—for example, term1.

Configure term behavior. For example, you might want to configure the dialer filter to allow only traffic between the branch office router and the head office router over the backup USB modem connection. In this example, the branch office router has the IP address 20.20.90.4/32 and the head office router has the IP address 200.200.201.1/32.

To configure the term completely, include both from and then statements.

  1. Enter

    edit term term1

  2. Enter

    set from source-address 20.20.90.4/32

  3. Enter

    set from destination-address 200.200.201.1/32

Configure the then part of the dialer filter to discard Telnet traffic between the branch office router and the head office router.

Enter

set then note

Table 67: Applying the Dialer Filter to the Dialer Interface

Task

CLI Configuration Editor

Navigate to the Interfaces level in the configuration hierarchy.

From the [edit] hierarchy level, enter

edit interfaces dl0 unit 0

Select the dialer interface to apply the filter—for example, dl0.

 

Apply the dialer filter to the dialer interface.

  1. Enter

    edit family inet filter

  2. Enter

    set dialer interesting-traffic

Configuring Dialer Watch for USB Modem Dial Backup

Dialer watch is a backup method that integrates backup dialing with routing capabilities and provides reliable connectivity without relying on a dialer filter to trigger outgoing USB modem connections. With dialer watch, the device monitors the existence of a specified route and if the route disappears, the dialer interface initiates the USB modem connection as a backup connection.

In this example, you configure dialer watch to enable the device to monitor the existence of the route to the head office router and initiate USB modem backup connectivity if the route disappears.

To configure dialer watch, you first add a dialer watch interface and then configure the USB modem interface to participate as a dialer watch interface.

To configure a dialer watch:

  1. Navigate to the top of the interfaces configuration hierarchy.
  2. Perform the configuration tasks described in Table 68.
  3. Go on to Table 69.
  4. When you are finished configuring the device, commit the configuration.

Table 68: Adding a Dialer Watch Interface

Task

CLI Configuration Editor

Navigate to the Interfaces level in the configuration hierarchy.

From the [edit] hierarchy level, enter

edit interfaces

Select a dialer interface—for example, dl0.

Adding a description, such as dialer-watch, can help you identify one dialer interface from another.

  1. Enter

    edit dl0

  2. Enter

    set description dialer-watch

On a logical interface—for example, 0—configure the route to the head office router for dialer watch—for example, 200.200.201.1/32.

  1. Enter

    edit unit 0 dialer-options

  2. Enter

    set watch-list 200.200.201.1/32

Configure the name of the dialer pool to use for dialer watch—for example, dw-pool.

Enter

set pool dw-pool

Table 69: Configuring a USB Modem Interface for Dialer Watch

Task

CLI Configuration Editor

Navigate to the Interfaces level in the configuration hierarchy, and select the USB modem physical interface umd0.

From the [edit] hierarchy level, enter

edit interfaces umd0 dialer-options pool dw-pool

Configure dialer watch options for the USB modem interface participating in the dialer watch.

The USB modem interface must have the same pool identifier to participate in dialer watch. Therefore, the dialer pool name dw-pool, for the dialer watch interface configured in Table 68, is used when configuring the USB modem interface.

 

Configuring Dial-In for a USB Modem Connection

You can configure a dialer interface to accept all incoming calls or accept only calls from one or more caller IDs.

If the dialer interface is configured to accept only calls from a specific caller ID, the device matches the incoming call's caller ID against the caller IDs configured on its dialer interfaces. If an exact match is not found and the incoming call's caller ID has more digits than the configured caller IDs, the device performs a right-to-left match of the incoming call's caller ID with the configured caller IDs and accepts the incoming call if a match is found. For example, if the incoming call's caller ID is 4085321091 and the caller ID configured on a dialer interface is 5321091, the incoming call is accepted. Each dialer interface accepts calls from only callers whose caller IDs are configured on it.

To configure a dialer interface for USB modem dial-in:

  1. Navigate to the top of the configuration hierarchy.
  2. Perform the configuration tasks described in Table 70.
  3. If you are finished configuring the device, commit the configuration.

Table 70: Configuring the Dialer Interface for USB Modem Dial-In

Task

CLI Configuration Editor

Navigate to the Interfaces level in the configuration hierarchy, and select a dialer interface—for example, dl0.

From the [edit] hierarchy level, enter

edit interfaces dl0

On logical interface 0, configure the incoming map options for the dialer interface.

  • accept-all—Dialer interface accepts all incoming calls.

    You can configure the accept-all option for only one of the dialer interfaces associated with a USB modem physical interface. The dialer interface with the accept-all option configured is used only if the incoming call's caller ID does not match the caller IDs configured on other dialer interfaces.

  • caller—Dialer interface accepts calls from a specific caller ID—for example, 4085551515. You can configure a maximum of 15 caller IDs per dialer interface.

    The same caller ID must not be configured on different dialer interfaces. However, you can configure caller IDs with more or fewer digits on different dialer interfaces. For example, you can configure the caller IDs 14085551515, 4085551515, and 5551515 on different dialer interfaces.

  1. Enter

    edit unit 0

  2. Enter

    edit dialer-options

  3. Enter

    set incoming-map caller 4085551515

Configuring PAP on Dialer Interfaces (Optional)

You can configure dialer interfaces to support the Password Authentication Protocol (PAP). PAP allows a simple method for a peer to establish its identity using a two-way handshake during initial link establishment. After the link is established, an ID and password pair is repeatedly sent by the peer to the authenticator until authentication is acknowledged or the connection is terminated.

For more information about PAP, see the Junos Network Interfaces Configuration Guide.

To configure PAP on the dialer interface, create an access profile and then configure the dialer interface:

  1. Navigate to the top of the configuration hierarchy.
  2. Perform the configuration tasks described in Table 71.
  3. If you are finished configuring the device, commit the configuration.

Table 71: Configuring PAP on Dialer Interfaces

Task

CLI Configuration Editor

Define a PAP access profile—for example, pap-access-profile with a client (username) named pap-access-user and the PAP password my-pap.

From the [edit] hierarchy level, enter

set access profile pap-access-profile client pap-access-user pap-password my-pap

Navigate to the appropriate dialer interface level in the configuration hierarchy—for example, dl0 unit 0.

From the [edit] hierarchy level, enter

edit interfaces dl0 unit 0

Configure PAP on the dialer interface and specify the local name and password—for example, pap-access-profile and my-pap.

Enter

set ppp-options pap local-name pap-access-user local-password my-pap

Configuring CHAP on Dialer Interfaces (Optional)

You can optionally configure dialer interfaces to support the PPP Challenge Handshake Authentication Protocol (CHAP). CHAP is a server-driven, three-step authentication method that depends on a shared secret password residing on both the server and the client. When you enable CHAP on a dialer interface, the device can authenticate its peer and be authenticated by its peer.

For more information about CHAP, see the Junos Network Interfaces Configuration Guide.

To configure CHAP on the dialer interface:

  1. Navigate to the top of the configuration hierarchy.
  2. Perform the configuration tasks described in Table 72.
  3. If you are finished configuring the device, commit the configuration.

Table 72: Configuring CHAP on Dialer Interfaces

Task

CLI Configuration Editor

Define a CHAP access profile—for example, usb-modem-access-profile with a client (username) named usb-modem-user and the secret (password) my-secret.

From the [edit] hierarchy level, enter

set access profile usb-modem-access-profile client usb-modem-user chap-secret my-secret

Navigate to the appropriate dialer interface level in the configuration hierarchy—for example, dl0 unit 0.

From the [edit] hierarchy level, enter

edit interfaces dl0 unit 0

Configure CHAP on the dialer interface and specify a unique profile name containing a client list and access parameters—for example, usb-modem-access-profile.

Enter

set ppp-options chap access-profile usb-modem-access-profile

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