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Configuration Guide - VPN

CloudEngine 12800 and 12800E V200R005C10

This document describes the configurations of VPN, including GRE, BGP/MPLS IP VPN, BGP/MPLS IPv6 VPN, VLL, PWE3, and VPLS.
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HVPLS

HVPLS

Hierarchical Virtual Private LAN Service (HVPLS) is a technology for hierarchizing the VPLS network.

Background of HVPLS

In VPLS using LDP signaling, the basic mechanism to prevent loops is to set up a full mesh of all the sites. LDP sets up LDP sessions of full mesh between all the sites. During packet forwarding, the packet from a PW is not forwarded to other PWs according to the scheme of split horizon. If a VPLS network has N PEs, the VPLS has N x (N - 1)/2 connections. When the number of PEs increases, the number of VPLS connections increases by N2. For example, if the number of sites is 100, the number of LDP sessions between sites is 4950.

The HVPLS can solve the problem of excessive connections and improve the network scalability. HVPLS is introduced in draft-ietf-l2vpn_vpls_ldp. The HVPLS hierarchize the network into different levels. The network of each level is of the full mesh type. Devices of different levels are connected through PWs and forward packets to each other without complying with the split horizon scheme.

HVPLS Model

Figure 6-9 shows the basic HVPLS model.

Figure 6-9 HVPLS Model

In a basic HVPLS model, PEs can be classified into the following types:

  • User-end provider edge (UPE): A customer convergence device that is directly connected to a CE. A UPE needs to be connected to only one PE in a fully-meshed VPLS network. A UPE supports routing and MPLS encapsulation. If a UPE is connected to multiple CEs and is capable to provide the basic bridging function, frame forwarding is performed only on the UPE. This reduces the burden on the SPE.

  • Superstratum provider edge (SPE): A device that is connected to a UPE and is located in the core of a fully-meshed VPLS network. The SPE is connected to all the devices in a fully-meshed VPLS network.

For the perspective of an SPE, a UPE functions like a CE. In data forwarding, an SPE uses the PW established between itself and a UPE as an AC. The UPE adds double MPLS labels to packets sent by CEs. The outer layer is an LSP label that is switched when a packet passes through devices on the access network. The inner label is a VC label that identifies a VC. After receiving double-tagged packets, an SPE directly removes the outer label, a statically configured public network label and determines the VSI which the static virtual circuit (SVC) accesses based on the inner label.

HVPLS Access Mode

The device only supports LDP HVPLS. A UPE connects to an SPE through LSPs.

Figure 6-10 HVPLS access in LSP mode

Figure 6-10 shows that UPE1 functions as a convergence device. UPE1 sets up a VC only with SPE1 to access a PW. UPE1 does not set up any VCs with other peers. The PW between a UPE and an SPE is called U-PW; the PW between SPEs is called S-PW.

The process of packet forwarding is described considering the example of CE1 sending packets to CE 2:

  1. CE1 sends a packet to UPE1. The destination MAC address of the packet is CE2.

  2. UPE1 is responsible for forwarding the packet sent by CE1 to SPE1. UPE1 adds double MPLS labels to this packet. The outer label identifies the LSP tunnel between UPE1 and SPE1; the inner label identifies the VC between UPE1 and SPE1.

  3. The LSR between UPE1 and SPE1 transmits the packet and switches labels of the packet. The outer label is stripped at the penultimate hop.

  4. After receiving the packet, SPE1 judges the VSI that the packet belongs to according to the MPLS inner label and finds that the packet belongs to VSI 1.

  5. SPE1 strips the MPLS inner label added to the packet by UPE1.

  6. SPE1 examines the entry of the VSI according to the destination MAC address of the packet, and finds that this packet needs to be sent to SPE2. SPE1 adds double MPLS labels to this packet. The outer label identifies the LSP tunnel between SPE1 and SPE2; the inner label identifies the VC between SPE1 and SPE2.

  7. The LSR between SPE1 and SPE2 transmits the packet and switches labels of the packet. The outer label is stripped at the penultimate hop.

  8. After receiving the packet from the S-PW side, SPE2 judges the VSI that the packet belongs to according to the MPLS inner label, and finds that the packet belongs to VSI 1. SPE2 strips the MPLS inner label added to the packet by SPE1.

  9. SPE2 adds double MPLS labels to this packet. The outer label identifies the LSP tunnel between SPE2 and UPE2; the inner label identifies the VC between UPE2 and SPE2. SPE2 then forwards the packet.

  10. The LSR between SPE1 and UPE2 transmits the packet and switches labels of the packet. The outer label is stripped at the penultimate hop.

  11. After receiving the packet, UPE2 strips the MPLS inner label added to the packet by UPE2. UPE2 examines the entry of the VSI according to the destination MAC address of the packet, and finds that the packet is to be sent to CE2. UPE2 then forwards this packet.

As shown in Figure 6-10, CE1 and CE4 access the same PE. The UPE directly forwards the packet between CE1 and CE4 without sending the packet to SPE1, because the UPE itself has the bridge function. However, for the first packet or broadcast packet with unknown destination MAC address sent from CE1, UPE1 broadcasts the packet to CE4 and forwards the packet to SPE1 through the U-PW. SPE1 copies the packet and forwards the packet to each peer CE.

HVPLS Loop Prevention

Compared with VPLS loop prevention, the HVPLS loop prevention differs in the following aspects:
  • Full-mesh connections (full-mesh PWs) only need to be set up between SPEs, and are not required between UPEs and SPEs.
  • An SPE does not forward packets received from the PW connected to the SPE to PWs that are associated with the VSI or PWs connected to other SPEs. The SPE forwards such packets to PWs connected to UPEs.
  • An SPE forwards packets received from the PW connected to a UPE to all PWs that are associated with the VSI and connected to other SPEs.
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Updated: 2019-04-03

Document ID: EDOC1100075353

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