Chapter 6 Broadband
VMG5313-B10A/-B30A Series User’s Guide
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VLAN also increases network performance by limiting broadcasts to a smaller and more
manageable logical broadcast domain. In traditional switched environments, all broadcast packets
go to each and every individual port. With VLAN, all broadcasts are confined to a specific broadcast
domain.
Introduction to IEEE 802.1Q Tagged VLAN
A tagged VLAN uses an explicit tag (VLAN ID) in the MAC header to identify the VLAN membership
of a frame across bridges - they are not confined to the switch on which they were created. The
VLANs can be created statically by hand or dynamically through GVRP. The VLAN ID associates a
frame with a specific VLAN and provides the information that switches need to process the frame
across the network. A tagged frame is four bytes longer than an untagged frame and contains two
bytes of TPID (Tag Protocol Identifier), residing within the type/length field of the Ethernet frame)
and two bytes of TCI (Tag Control Information), starts after the source address field of the Ethernet
frame).
The CFI (Canonical Format Indicator) is a single-bit flag, always set to zero for Ethernet switches. If
a frame received at an Ethernet port has a CFI set to 1, then that frame should not be forwarded as
it is to an untagged port. The remaining twelve bits define the VLAN ID, giving a possible maximum
number of 4,096 VLANs. Note that user priority and VLAN ID are independent of each other. A
frame with VID (VLAN Identifier) of null (0) is called a priority frame, meaning that only the priority
level is significant and the default VID of the ingress port is given as the VID of the frame. Of the
4096 possible VIDs, a VID of 0 is used to identify priority frames and value 4095 (FFF) is reserved,
so the maximum possible VLAN configurations are 4,094.
Multicast
IP packets are transmitted in either one of two ways - Unicast (1 sender - 1 recipient) or Broadcast
(1 sender - everybody on the network). Multicast delivers IP packets to a group of hosts on the
network - not everybody and not just 1.
Internet Group Multicast Protocol (IGMP) is a network-layer protocol used to establish membership
in a Multicast group - it is not used to carry user data. IGMP version 2 (RFC 2236) is an
improvement over version 1 (RFC 1112) but IGMP version 1 is still in wide use. If you would like to
read more detailed information about interoperability between IGMP version 2 and version 1, please
see sections 4 and 5 of RFC 2236. The class D IP address is used to identify host groups and can be
in the range 224.0.0.0 to 239.255.255.255. The address 224.0.0.0 is not assigned to any group
and is used by IP multicast computers. The address 224.0.0.1 is used for query messages and is
assigned to the permanent group of all IP hosts (including gateways). All hosts must join the
224.0.0.1 group in order to participate in IGMP. The address 224.0.0.2 is assigned to the multicast
routers group.
At start up, the VMG queries all directly connected networks to gather group membership. After
that, the VMG periodically updates this information.
DNS Server Address Assignment
Use Domain Name System (DNS) to map a domain name to its corresponding IP address and vice
versa, for instance, the IP address of www.zyxel.com is 204.217.0.2. The DNS server is extremely
TPID
2 Bytes
User Priority
3 Bits
CFI
1 Bit
VLAN ID
12 Bits
Summary of Contents for VMG5313-B10A
Page 15: ...15 PART I User s Guide ...
Page 16: ...16 ...
Page 32: ...Chapter 2 The Web Configurator VMG5313 B10A B30A Series User s Guide 32 ...
Page 40: ...Chapter 4 Tutorials VMG5313 B10A B30A Series User s Guide 40 ...
Page 71: ...71 PART II Technical Reference ...
Page 72: ...72 ...
Page 78: ...Chapter 5 Network Map and Status Screens VMG5313 B10A B30A Series User s Guide 78 ...
Page 106: ...Chapter 6 Broadband VMG5313 B10A B30A Series User s Guide 106 ...
Page 162: ...Chapter 9 Routing VMG5313 B10A B30A Series User s Guide 162 ...
Page 180: ...Chapter 10 Quality of Service QoS VMG5313 B10A B30A Series User s Guide 180 ...
Page 198: ...Chapter 11 Network Address Translation NAT VMG5313 B10A B30A Series User s Guide 198 ...
Page 210: ...Chapter 14 Interface Group VMG5313 B10A B30A Series User s Guide 210 ...
Page 218: ...Chapter 15 USB Service VMG5313 B10A B30A Series User s Guide 218 ...
Page 232: ...Chapter 17 Firewall VMG5313 B10A B30A Series User s Guide 232 ...
Page 240: ...Chapter 19 Parental Control VMG5313 B10A B30A Series User s Guide 240 ...
Page 250: ...Chapter 21 Certificates VMG5313 B10A B30A Series User s Guide 250 ...
Page 296: ...Chapter 23 Voice VMG5313 B10A B30A Series User s Guide 296 ...
Page 300: ...Chapter 24 Log VMG5313 B10A B30A Series User s Guide 300 ...
Page 308: ...Chapter 27 xDSL Statistics VMG5313 B10A B30A Series User s Guide 308 ...
Page 318: ...Chapter 30 Remote Management VMG5313 B10A B30A Series User s Guide 318 ...
Page 322: ...Chapter 32 TR 064 VMG5313 B10A B30A Series User s Guide 322 ...
Page 332: ...Chapter 36 Log Setting VMG5313 B10A B30A Series User s Guide 332 ...
Page 336: ...Chapter 37 Firmware Upgrade VMG5313 B10A B30A Series User s Guide 336 ...
Page 352: ...Chapter 40 Troubleshooting VMG5313 B10A B30A Series User s Guide 352 ...
Page 354: ...354 ...
Page 374: ...Appendix B Wireless LANs VMG5313 B10A B30A Series User s Guide 374 ...
Page 390: ...Appendix E Legal Information VMG5313 B10A B30A Series User s Guide 390 ...