Juniper JUNOSE 11.1.X - LINK LAYER CONFIGURATION 4-7-2010, Configuration Manual

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More specifically, a transparent bridge performs all of the following actions to learn
the network topology:
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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.
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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.
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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.
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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.
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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 43 on page 469 shows an example of a simple transparent bridging network
configuration that illustrates the concepts discussed so far in this section.
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Overview
JUNOSe 11.1.x Link Layer Configuration Guide