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Chapter 1. Understanding SDSL and the Express L768
Routing and Bridging with the Express L768
The Express L768 is a Router and Transparent Learning Bridge. Its fea-
tures can be easily configured and used once several basic concepts
are understood.
Factory Default
The Express L768 comes from the factory configured for MAC Bridg-
ing with no filters or connection information defined. An IP address of
10.0.0.1 with a network mask of 255.255.255.0 is preloaded. The facto-
ry default layer two configuration is Auto Detect, which automatically
detects PPP or Frame Relay.
Bridging
In Bridge Mode, the Express L768 can be used to connect two LAN
segments. In this mode, all protocols are supported because they are
transported across the SDSL link at the MAC layer. The Spanning Tree
Algorithm can be used to guarantee a loop-free topology. MAC ad-
dresses are "learned" by each Express L768 to prevent non-WAN
packets from being bridged.
IP Routing
The Express L768 operates as an IP router when the Configuration/IP/
IP Router/Mode option is configured to On. In PPP mode, the Express
L768 uses an IP unnumbered WAN interface; the IP address and mask
assigned to the unit's LAN interface apply to all routing and IP oper-
ations for the unit. In Frame Relay mode, each PVC can be specified
as numbered or unnumbered links. If a default gateway is specified on
the network of the Ethernet interface, the unit attempts to reach the
gateway through that interface. If no default gateway is specified (i.e.,
0.0.0.0) the WAN interface becomes the default gateway (recommend-
ed for remote applications when there are no other routers on the re-
mote LAN).
1-6
Express L768 User Manual
61203192L1-20
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