ZyXEL Communications VES-1000 Series, Руководство пользователя, Страница: 42 / 227

VES-1000 Series Ethernet Switch
5-2 Getting Started Screens
5.2.1 Ethernet Port Trunking
Ethernet port trunking lets you aggregate the Ethernet ports into one logical link. The VES uses MAC-based load
balancing which analyzes a packet’s source and destination MAC addresses to distribute the load between the two
Ethernet ports when uplinking to the remote switch.
The remote switch to which the VES connects must also support Ethernet port trunking. The
load-balancing method, however, does not have to be the same as on the VES.
Note that the two uplink ports must be connected to a single remote switch when port trunking is enabled. Disable
trunking (default) if you wish to daisy-chain other VES-1000 Series VDSL switches. Daisy-chaining VES-1000
Series switches does degrade performance.
5.3 IGMP Snooping
Traditionally, IP packets are transmitted in one of either two ways - Unicast (one sender to one recipient) or
Broadcast (one 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.
5.4 Introduction to Spanning Tree Protocol (STP)
The use of STP in the majority of network environments is not recommended. Furthermore, this rarely used feature
should not be enabled on the VDSL ports on the VES-1000 Series of switches.
STP detects and breaks network loops and provides backup links between switches, bridges or routers. It allows a
device to interact with other STP-aware devices in your network to ensure that only one path exists between any
two stations on the network.
5.4.1 STP Terminology
The root bridge is the base of the spanning tree; it is the bridge with the lowest identifier value (MAC address).