Specifying a USB Modem Interface on J-series Routers

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The J-series Services Routers contain two USB ports controlled by a single USB controller. One USB port can support USB devices, while the other one can act as a USB modem.

The USB modem provides a dial-in remote management interface, and supports dialer interface features by sharing the same dial pool as a dialer interface. The dial pool allows the logical dialer interface (dln) and the physical interface (umd0) to be bound together dynamically on a per-call basis.

The following dialer interface features are supported by the USB modem interface:

Encapsulation PPP
CoS
NAT
Interface statistics
Packet capture
GRE tunnel
Stateful firewall
Traffic sampling

To configure a USB modem interface, include the following statements at the [edit interfaces] hierarchy level:



[edit interfaces]
umd0 {



dialer-options {

pool pool-name <priority priority>;
}





modem-options {

dialin (console
| routable);
init-command-string initialization-command-string;
}


}

The pool name specified at the [edit interfaces umd0 dialer-options pool] hierarchy level must be the same as the pool name specified at the [edit interfaces dln unit logical-unit-number dialer-options pool] hierarchy level.

Configure the USB modem to operate as a dial-in WAN backup interface by including the dialin statement and specifying the routable option. If the USB modem is to be used as a dial-in console, specify the console option in the dialin statement.

When the Services Router applies the modem AT commands configured in the init-command-string statement or the default sequence of initialization commands to the modem, it compares them to the initialization commands already configured on the modem and makes the following changes:

If the commands are the same, the router overrides the existing modem values that do not match. For example, if the initialization commands on the modem include S0=0 and the router’s init-command-string configuration includes S0=2, the Services Router applies S0=2.
If the initialization commands on the modem do not include a command in the router’s init-command-string statement configuration, the router adds it. For example, if the init-command-string statement includes the command L2, but the modem commands do not include it, the router adds L2 to the initialization commands configured on the modem.

Include the following statements at the [edit interfaces dln] hierarchy level to support a minimum configuration for a dialer interface connected to a USB modem:



[edit interfaces dln]

encapsulation ppp;
unit logical-unit-number;
dialer-options {
dial-string dial-string-numbers;
pool pool-name <priority priority>;
}

ppp-options {
chap;
access-profile name;
local-name name;
passive;
}

family inet {

mtu bytes;



address address {

destination address;
}


}

For more information about configuring dial-in, see Configuring ISDN Logical Interface Properties.

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