ADTRAN L128T user manual IP Routing

Chapter 1: Understanding ISDN and the Express L128/L128T

IP Routing

The Express L128/L128T operates as a dial-up IP router when the Configura- tion/IP/IP Router/Mode option is configured to On. The Express L128/L128T 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 speci- fied 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 con- nection. If no default gateway is specified, the first connected peer on the WAN interface becomes the default gateway (recommended for remote appli- cations 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 L128/L128T 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.

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