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VPLS packet encapsulation
Packet encapsulation on an AC
The packet encapsulation type of an AC depends on the user VSI access mode, which can be VLAN
or Ethernet.
•
VLAN
access
—The Ethernet header of a packet sent by a CE to a PE or sent by a PE to a CE
includes a VLAN tag that is added in the header as a service delimiter for the service provider
network to identify the user. The tag is called a "P-Tag."
•
Ethernet
access
—The Ethernet header of a packet upstream from the CE or downstream from
the PE does not contain any service delimiter. If a header contains a VLAN tag, it is the internal
VLAN tag of the user and means nothing to the PE. This kind of internal VLAN tag of the user is
called a "U-Tag."
You can specify the VSI access mode to be used.
Packet encapsulation on a PW
The packet encapsulation type of a PW, also called the "PW transport mode," can be either Ethernet
or VLAN.
•
In Ethernet mode, P-Tag is not transferred on the PW. For a packet from a CE, if it contains the
service delimiter, the PE removes the service delimiter and adds a PW label and a tunnel label
into the packet before forwarding the packet. Otherwise, the PE adds a PW label and a tunnel
label into the packet and then forwards the packet. For a packet to be sent downstream,
whether the PE adds the service delimiter into the packet depends on your configuration.
However, rewriting and removing the existing tags are not allowed.
•
In VLAN mode, packets transmitted over the PW must carry a P-Tag. For a packet from a CE, if
it contains the service delimiter, the PE keeps the P-Tag unchanged or changes the P-Tag to the
VLAN tag expected by the peer PE or to a null tag (the tag value is 0), and then adds a PW label
and a tunnel label into the packet before sending the packet out. If the packet contains no
service delimiter, the PE adds the VLAN tag expected by the peer PE or a null tag, and then a
PW label and a tunnel label into the packet before sending the packet out. For a packet to be
sent downstream, the PE rewrites, removes, or retains the service delimiter depending on your
configuration.
According to the protocol, the packet encapsulation type of a PW is VLAN by default.
H-VPLS implementation
Hierarchy of VPLS (H-VPLS) can extend the VPLS access range of a service provider and reduce
costs.
Advantages of H-VPLS access
•
H-VPLS has lower requirements on the multi-tenant unit switch (MTU-s). It has distinct
hierarchies which fulfill definite tasks.
•
H-VPLS reduces the logical complexity of the fully meshed network consisting of PEs and the
configuration complexity.