User`s guide

Configuring the Pipeline as a Bridge
Introduction to Ascend bridging
5-2 Preliminary January 30, 1998 Pipeline User’s Guide
Routing is much faster than bridging, and has these advantages:
• Routers examine packets at the network layer, so you can filter on logical
addresses, providing enhanced security and control.
• Routers support multiple transmission paths to a given destination,
enhancing the reliability and performance of packet delivery.
From a practical point of view, you should always route if possible, as routing is
more efficient and makes call management easier. Bridging is necessary when
you cannot subnet your IP network, and when you need to use non-routable
protocols such as AppleTalk, NetBIOS, or DECnet.
How a bridged WAN connection is initiated
When the Pipeline is configured for bridging, it accepts all packets on the
Ethernet and forwards only those that have one of the following:
• A physical address that is not on the segment connected to the Pipeline
• A broadcast address
Bridging uses physical or broadcast addresses, not logical (network) addresses.
Physical addresses and the bridge table
A physical address is a unique hardware-level address associated with a specific
network controller. A device’s physical address is also called its Media Access
Control (MAC) address. On Ethernet, the physical address is a six-byte
hexadecimal number assigned by the Ethernet hardware manufacturer, as in:
0000D801CFF2
If the Pipeline receives a packet whose destination MAC address is not on the
local network, it checks its internal bridge table. If it finds the packet’s MAC
address, the Pipeline dials the connection and bridges the packet. If the address is
not found, the Pipeline checks for active sessions that have bridging enabled. If
there are active bridging links, the Pipeline forwards the packet across all active
sessions that have bridging enabled.
Note:
The Pipeline cannot dial a connection for packets that are not on the local
network and not specified in its bridge table because it has no way of finding the
proper Connection profile. See “Managing the bridge table” on page 5-7.