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Operation Manual – VPLS
H3C S9500 Series Routing Switches
Chapter 1 VPLS Configuration
1-5
Remote MAC addresses learned by a PE that are related to VC labels but no more in
use need to be aged out by an aging mechanism. The aging mechanism used here is
the aging timer corresponding to the MAC address. When receiving a packet whose
source MAC address has an aging timer started, the PE resets the aging timer.
III. VPLS loop avoidance
Generally, Layer 2 networks use spanning tree protocol (STP) to avoid loops. For users
using the VPLS solution, they cannot sense the Internet service provider’s network
(ISP network), and therefore they will not take the ISP network into account when
configuring STP in their private networks. In a VPLS network, horizontal split is used to
avoid loops.
Two methods for VPLS loop avoidance are supported:
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PEs are logically fully meshed (so are PWs), that is, each PE must create for each
VPLS forwarding instance a tree to all the other PEs of the instance.
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Each PE must support horizontal split to avoid loops, that is, a PE cannot forward
packets via PWs of the same VSI instance, because all the PEs of a VSI instance
are directly connected. In other words, packets from PWs on the public network
side cannot be forwarded to other PWs; they can only be forwarded to the private
network side.
IV. Peer PE discovery and PW signaling protocol
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For PE devices in the same VSI, you can configure the remote PE addresses
manually or using an automatic discovery mechanism. Currently, LDP and BGP
can be used to automatically discover VSI peer PEs, and the extensions of the two
protocols can be used as the PW signaling protocol to create PWs.
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The PW signaling protocol is designed to assign multiplex distinguishing flags
(that is, VC labels) and advertise the assigned VC flags to the peer. In addition, the
PW signaling protocol advertises VPLS system parameters such as PW ID,
control word, and interface parameters. With the PW signaling protocol, fully
meshed PWs can be established between PEs for VPLS services.
1.1.2 VPLS Packet Structure
I. Packet encapsulation on an AC
The packet encapsulation type of an AC depends on the user VSI access mode: VLAN,
Ethernet.
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VLAN access: The Ethernet header of a packet transferred between CE and PE
includes a VLAN tag, which is added in the header as a service delimiter for the
service provider network to identify the user. The tag is also called P-TAG.