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Chapter 1: Understanding ISDN and the Express XL/XLT
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Express XL/XLT User Manual
61200070L1-1
IP Routing 
The Express XL/XLT operates as a dial-up IP router when the Configuration/
IP/IP Router/Mode
 option is configured to On.  The Express XL/XLT uses an 
IP unnumbered WAN interface; the IP address and mask assigned to the unit’s 
LAN interface apply to all routing and IP operations for the unit.  If a default 
gateway is specified on the network of the Ethernet interface, the unit attempts 
to reach the gateway through that interface.  If the gateway is specified on an 
unknown network, the unknown network is assigned to the router table and 
remains unused until that gateway becomes the peer on a WAN connection.  
If no default gateway is specified, the first connected peer on the WAN inter-
face becomes the default gateway (recommended for remote applications 
when there are no other routers on the remote LAN).
For each profile in the Connection List that includes an IP address and has the 
Configuration/Connection List/IP/Route/Static Route
 option set to Yes, the 
Network Address of the specified IP address is added to the router table with 
the Host Address as the gateway.  If the Configuration/Connection List/IP/
Route/Private 
option is set to No, the route is advertised at the specified metric 
through the unit’s interfaces as if a connection is active to that network.  These 
routes are referred to as spoofed routes
Attempts by any computer connected to the LAN interface to access a host on 
a spoofed network causes a connection to be attempted using the information 
from that Connection List profile. Once connected, routes advertised by the 
peer router are learned and advertised to the local LAN.  If Bandwidth-On-De-
mand is enabled and an Idle Time-out value is specified, expiration of the Idle 
Timer causes the link to be disconnected; the routes learned from the peer 
router are retained if the Configuration/Connection List/IP/RIP/Retain op-
tion is set to Yes and advertised as if the connection is still active.  These routes 
are referred to as retained routes.  Attempts by any connected computer to ac-
cess a host on any of the retained routes causes the link to be redialed.  If Hang 
Up
 is activated from the Dial menu when the link is down, the retained routes 
are removed.
The Express XL/XLT can be connected to two WAN destinations at the same 
time. Each B-channel is dialed to a different location. Routes learned from one 
WAN destination are advertised to the other using RIP.