ZyXEL Communications ALC1024, User Manual

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Commands with EEC
Bridge Commands 7-1
Chapter 7
Bridge Commands
This chapter discusses the bridge subsystem. It allows you to configure and monitor bridging, configure
MAC filters, port-based VLANs and tagged frame functions of the line cards.
7.1 Bridging Overview
The line card supports IEEE 802.1D transparent bridging; but not the static filtering feature or spanning tree
protocol. The bridge learns the source MAC addresses of sender hosts by inspecting incoming Ethernet frames
and recording the learned MAC addresses with their incoming port numbers into its filtering database. Based on
the database, the bridge forwards each incoming frame to its destination port.
7.2 IGMP Snooping
Traditionally, IP packets are transmitted in one of either two ways - Unicast (1 sender to 1 recipient) or Broadcast
(1 sender to everybody on the network). Multicast delivers IP packets to just a group of hosts on the network.
IGMP (Internet Group Multicast Protocol) is a session-layer protocol used to establish membership in a multicast
group - it is not used to carry user data. Refer to
RFC 1112 and RFC 2236 for information on IGMP versions 1
and 2 respectively.
A layer-2 switch can passively snoop on IGMP Query, Report and Leave (IGMP version 2) packets transferred
between IP multicast routers/switches and IP multicast hosts to learn the IP multicast group membership. It checks
IGMP packets passing through it, picks out the group registration information, and configures multicasting
accordingly.
Without IGMP snooping, multicast traffic is treated in the same manner as broadcast traffic, that is, it is forwarded
to all ports. With IGMP snooping, group multicast traffic is only forwarded to ports that are members of that
group. IGMP Snooping generates no additional network traffic, allowing you to significantly reduce multicast
traffic passing through your switch.
7.3 Bridge Port Numbers
The bridge subsystem of the line card defines its own numbering convention for ports.
The bridge has a total of 25 ports: bridge port 1 stands for the Ethernet port, bridge port 2
stands for DSL port 1, bridge port 3 stands for DSL port 2, and so on.
Be sure you have clarified the relation between bridge ports and DSL ports.
7.4 Basic Commands
Below is a list of commonly-used bridge commands.