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More specifically, a transparent bridge performs all of the following actions to learn the
network topology:
•
Learning—The bridge examines the MAC address of every incoming packet, records
the MAC address and associated interface in the forwarding table, and manages the
database of MAC addresses and their associated interfaces.
•
Flooding—When a packet’s destination address does not match any entries in the
forwarding table, the bridge transmits (floods) the packet on all bridge interfaces to
all network segments except the interface on which the packet was received.
• Forwarding—Once the bridge has learned a packet’s destination address (that is, has
a matching entry in its forwarding table), the bridge uses the associated port and
interface information to send the packet toward its destination.
• Filtering—If the bridge detects that a packet’s source and destination addresses are
on the same network segment, it ignores (filters) that packet.
Filtering is the process
by which the bridge can screen network traffic for certain characteristics and determine
whether to forward or discard (drop) that traffic based on user-defined criteria. On
E Series routers, filtering criteria can include the MAC source address, MAC destination
address, and protocol type.
•
Aging—When a bridge adds a dynamic (learned) MAC address entry to the forwarding
table, it assigns an age to the entry. The bridge updates this age each time it receives
a packet. To manage MAC entries more efficiently, you can configure an entry’s aging
time, which is the maximum time that an entry can remain in the forwarding table
before it “ages out.”
Bridge Groups and Bridge Group Interfaces
You configure transparent bridging by creating one or more bridge groups on the router.
A
bridge group is a collection of network interfaces (ports) that forms a broadcast domain.
Each bridge group has its own set of forwarding tables and filters and, as such, functions
as a logical transparent bridging device. For information about the maximum number of
bridge groups that you can configure per E Series router, see
JunosE Release Notes ,
Appendix A , System Maximums .
After you create a bridge group, you associate one or more network interfaces with the
bridge group. This association is called a
bridge group interface , or simply bridge interface .
For information about the maximum number of bridge interfaces that you can configure
per line module and per E Series router, see
JunosE Release Notes , Appendix A , System
Maximums .
Figure 45 on page 467 shows an example of a simple transparent bridging network
configuration that illustrates the concepts discussed so far in this section.
Copyright © 2010, Juniper Networks, Inc. 466
JunosE 11.2.x Link Layer Configuration Guide