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Chapter 1: Understanding ISDN and the Express XL/XLT
14 Express XL/XLT User Manual 61200.070L1-1
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.