Vpls Packet Encapsulation; H-Vpls Implementation - HP 10500 SERIES Configuration Manual

Split horizon forwarding—Each PE must support horizontal split to avoid loops. A PE cannot
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forward packets through PWs of the same VSI, because all PEs of a VSI are directly connected.
Packets from PWs on the public network side cannot be forwarded to other PWs. They can only be
forwarded to the private network side.

VPLS packet encapsulation

This section describes different types of 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 the 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
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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."
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
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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.
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
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which fulfill definite tasks.
H-VPLS reduces the logical complexity of the fully meshed network consisting of PEs and the
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configuration complexity.
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