1.5 Administrator's Guide

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  4. Commissioning the unit
  5. Network configuration
  6. Ethernet Interface Configuration
  7. X21 Interface configuration

X21 Interface configuration

If the Com.X is equipped with an X.21 serial interface (typically for connection to leased line or frame relay services), the interface is listed as serial0 (X21-1) in the Interfaces list.

The Com.X X.21 interface is always DTE on the physical layer (although it may act as protocol DCE in Frame Relay mode). Therefore, the clock and thus the data rate of the interface is provided by the DCE equipment connected to the X.21 interface, typically an NTU.

<Figure 32: interfaces list showing serial0 X21 interface>

As with other network interfaces, the interface configuration may be edited by double-clicking the list entry. The availability of the different fields will depend on the Serial Protocol chosen.

<Figure 33: X21 interface configuration form>

The fields are described in the table below. Note that only PPP mode supports Automatic IP configuration.



Name (not editable)


Description (not editable)


Serial Protocol

IP/HDLC – Raw IP in HDLC encapsulation

Cisco HDLC – Cisco compatible IP HDLC encapsulation

Frame Relay – ANSI/CCITT (ITU) compatible frame relay encapsulation

PPP – Point-to-Point Protocol

Frame relay LMI

(Only enabled when Serial Protocol is Frame Relay) – Local Management Interface protocol selection. Valid values are:





Automatic IP

(only valid for PPP mode) – obtain IP address automatically from the PPP peer


Interface enabled/disabled at startup

IP Address

(except when Frame Relay or Automatic IP enabled) – IP address of this interface

Network Mask

(except when Frame Relay or PPP enabled) – Network mask of this interface

Gateway/Peer IP

(optional, not enabled when Frame Relay or PPP enabled) – Peer IP for point-to-point links, or gateway for multipoint

PPP attached device (not editable)

(only valid for PPP mode) /dev/ttyX0

PPP username

(only valid for PPP mode) PAP/CHAP username

PPP password

(only valid for PPP mode) PAP/CHAP password

PPP authorization

Method of PPP authorization:

PPP_NONE – don’t use PAP/CHAP

PPP_AUTO – use PAP or CHAP as required

PPP_PAP – use PAP only

PPP_CHAP – use CHAP only

PPP service name

(optional) PPP provider’s service name, normally left blank

Default metric

The metric of a network route is a property used by a routing protocol to determine whether one particular route should be chosen over another. In conflicting cases, traffic will be directed towards the gateway containing the lowest value metric.