Allied Telesis AT-9000 Series - Manual (Page 852)

Chapter 56: VLAN Stacking
824 Section III: File System
Components
There are four components to VLAN stacking:
 VLAN
 Customer ports
 Provider port
 EtherType/Length value
VLAN
The boundary between the customer’s network and the metro provider’s
network is marked by a VLAN. In cases where the switch is connected to
more than one customer, there has to be a different VLAN for each
customer.
The VID the VLAN is assigned has to be the VID that the metro provider
wants to assign to the 802.1Q header that identifies the customer packets
of that VLAN. For example, if a metro provider wants to assign the VID
110 to packets belonging to customer A, they would assign the VLAN the
VID 110.
Customer Ports
Switch ports connected to devices on the customer’s network are
designated as customer ports. There can be more than one customer port
in a VLAN.
Customer ports must be designated as untagged ports, meaning that they
have to be in the VLAN access mode. Typically, untagged ports do not
handle tagged packets. But with VLAN stacking, customer ports may
handle tagged or untagged packets.
The extra 802.1Q headers are added to or deleted from the packets at the
customer ports. The action of the ports depends on the direction of the
packets. The new 802.1Q header is added to ingress tagged or untagged
packets, prior to the packets being forwarded to the service provider port.
The header is removed from egress packets, which are packets that
customer ports are about to transmit to the customer’s network. The
headers are removed to return the packets to the same form that they had
prior to entering the service provider network.
Provider Ports
Provider ports are switch ports that are connected to devices on the metro
provider network. These ports have to be set to the tagged, trunk mode so
that they do not delete the 802.1Q headers the customer ports add to the
packets.
EtherType/
Length
This parameter specifies the protocol or length of the data in the payload
in the packets. Also known as the Tag Protocol Identifier (TPID), this
hexadecimal value has the range 0000 to FFFF. The EtherType/Length
value is set at the switch level. The default value is 0x8100.