Draytek VigorSwitch G1260, Руководство пользователя

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VigorSwitch G1260 User’s Guide 31
the traffic using that entry has yet come for a while. If this time period is more than the
aging time, the entry will be marked invalid. The vacancy is now available for other new
MAC.
Both learning and forwarding are the most important functions in a switch. Besides that,
VLAN can be one of the rules to forward the packet. There are ingress rule and egress rule
applied. The ingress rule is used to filter the incoming packet by VLAN ID and so on and
to decide whether the packet is allowed to enter the switch or not. The egress rule is used to
forward the packet to the proper port.
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There is a field in MAC address table used to put the entry’s Age time which determines
how long a MAC entry can reside in a switch. The age time is refreshed when a packet
with that SA. Usually, the age time is programmable.
T T r r a a n n s s m m i i s s s s i i o o n n s s c c h h e e d d u u l l e e
In most layer 2 switches, the QoS is supported. QoS in a switch must associate a
transmission schedule to transmit the packet. This function is much to do with the priority
level a packet has. With the given priority, the scheduler will do the proper action on it.
The scheduler has many ways to implement, and different chips may support different
schedule algorithms. Most common schedulers are:
FCFS: First Come First Service.
Strictly Priority: All High before Low.
Weighted Round Robin:
Set a weight figure to the packet with a priority level, say 5-7, and next, set another weight
to the packet with a priority level, say 2-4 and so on. The WRR will transmit the packet
with the weight. So the packet of each priority level can be allocated a fixed bandwidth.
B B a a n n d d w w i i d d t t h h r r a a t t i i n n g g
Bandwidth rating is the limitation set by administrator, and it can be applied to those with
SLA. Bandwidth rating can be total bandwidth, types of service of a port with many steps.
The switch supports by-port Ingress and Egress total bandwidth rate control capacity. The
bandwidth rate resolution is 0.1 Mbps (100Kbps) and ranges from 0 to 100Mbps.
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W W h h a a t t i i s s a a V V L L A A N N ? ?
It is a subset of a LAN. Before we discuss VLAN, we must understand what LAN is. In
general, a LAN is composed of different physical network segments bridged by switches or
bridges which attach to end stations in the same broadcast domain. The traffic can reach
any station on the same LAN. Beyond this domain, the traffic cannot go without router’s
help. This also implies that a LAN is limited. If you need to communicate with the station
outside the LAN, a router is needed which always lies on the edge of the LAN.
For a layer 2 VLAN, it assumes it is a logical subset of a physical LAN separated by
specific rules such as tag, port, MAC address and so on. In other words, they can
communicate with each other between separated small physical LANs within a LAN but
can not be between any two separated logical LANs.
(*
The switch image is sample only.)