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Feature Description - VPN 01

NE05E and NE08E V300R003C10SPC500

This is NE05E and NE08E V300R003C10SPC500 Feature Description - VPN
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Martini VPWS

Martini VPWS

Definition

Martini VPWS is an L2VPN technology that uses a point-to-point link to transmit traffic and uses LDP as the signaling protocol to transmit VC information.

Martini VPWS uses double labels. The inner label is exchanged using extended LDP, and the outer label is a tunnel label.

On a Martini VPWS network, multiple VCs can be established over an LSP between two PEs. In addition, PEs store only a small amount of L2VPN information, such as mappings between VC labels and LSPs. Ps, however, do not store any L2VPN information. Therefore, Martini VPWS has excellent scalability. To add a VC, you only need to configure a unidirectional VC on each endpoint PE. This operation does not affect network operation.

The LDP signaling protocol used by Martini VPWS is independent of the periodic refresh mechanism and therefore is faster in fault detection.

Basic Concepts

In Martini VPWS, the VC type and VC ID together uniquely identify a VC between CEs. The VC type indicates the encapsulation type of a VC, for example, Ethernet, or VLAN. The VC ID identifies a VC. VCs of the same type must have a unique ID on a PE.

The endpoint PEs exchange inner labels using LDP, and each CE is bound to the peer CE according to the VC ID. A VC can be successfully established if the following conditions are all met:

  • The physical status of AC interfaces is Up.
  • The tunnel between the PEs has been established.
  • Labels are exchanged between the PEs and each label is bound to a VC ID.

In Martini VPWS, the outer label is used to transmit the data of each VC over an ISP network, and the inner label is used to identify service data. An LSP on the ISP network can be shared by multiple VCs.

To support Martini VPWS, an ISP network must be able to automatically establish LSPs. That means that the ISP network must support MPLS forwarding and MPLS LDP.

Martini VPWS Network Topology

Figure 6-4 shows the Martini VPWS network topology.

Figure 6-4 Martini VPWS network topology

On the network shown in Figure 6-4, Site 1 and Site 2 of VPN1 are connected over a remote Martini connection (as indicated by the black dashed line). Site 1 and Site 2 of VPN2 are also connected over a remote Martini connection (as indicated by the blue dashed line). VPN1 and VPN2 communicate over two LSPs on the ISP network. They can also multiplex one LSP for communication.

PWE3 VPWS

PWE3 VPWS is a technology that simulates the basic behaviors and characteristics of services, such as ATM,Ethernet, low-speed TDM circuit, and SONET/SDH, on a PSN to transmit Layer 2 traffic.

PWE3 is an extension to the Martini protocol. By extending the new signaling, reducing the signaling cost, and defining the multi-segment negotiation mode, PWE3 improves networking flexibility. Compared with Martini VPWS, PWE3 VPWS exchanges fewer packets when the network is unstable, preventing repeated PW establishment and deletion.

  • PWE3 Networking Modes

    PWE3 VPWS has the following networking modes:
    • Single-segment PWE3 networking

      Single-segment PWE3 means that only one PW exists between two PEs, and no inner label switching is needed. Because the PW uses LDP as the signaling protocol to transmit VC information, an LDP session must be established between the PEs:

      • If a P exists between the PEs, a remote LDP session must be created.

      • If the PEs are directly connected, a local LDP session must be created.

      Figure 6-5 shows typical single-segment PWE3 networking.

      Figure 6-5 Single-segment PWE3 networking

    • Multi-segment PWE3 networking

      An MS-PW is a set of two or more PW segments that function as a single PW. The forwarding mechanisms of PEs for the SS-PW and MS-PW are the same. The only difference is that PW labels are switched on SPEs for MS-PWs. PW2 in Figure 6-6 is an example of an MS-PW.

      If two PEs cannot establish a connection using signaling or cannot establish a direct tunnel, configure an MS-PW between the two PEs instead. By supporting MS-PWs, PWE3 improves networking flexibility.

      Besides being classified as SS-PWs or MS-PWs, PWs can also be classified as static or dynamic. The two classification methods can be used together. For example, an MS-PW can be a set of static and dynamic PW segments.

      Figure 6-6 Networking diagram for the SS-PW and MS-PW

  • Dynamic PW

    A dynamic PW is a PW established using a signaling protocol. UPEs exchange VC labels using LDP and bind the corresponding CEs to AC interfaces based on VC IDs. A VC is established if all the following conditions are met:

    • The physical status of AC interfaces is Up.
    • The tunnel between the endpoint PEs has been established.
    • VC labels have been exchanged between the endpoint PEs and each VC label is bound to a VC ID.

    The messages for dynamic PWs are as follows:

    • Label Request: requests the peer PE to allocate a label.

    • Label Mapping: notifies the peer PE of the label allocated by the local PE. Whether the Label Mapping message carries the Status field depends on the default signaling. By default, Martini VPWS does not support the Status field.

    • Notification: notifies and negotiates the PW status, and reduces the number of exchanged messages.

    • Label Withdraw: carries the corresponding label and status information to notify the peer PE of withdrawing labels.

    • Label Release: responds to a Label Withdraw message, and instructs the peer that sends the Label Withdraw message to withdraw labels.

  • Establishment, Maintenance, and Deletion of Dynamic PWs

    Dynamic PWs are established using LDP signaling, and VC information is carried in the extended type-length-value (TLV) fields of LDP signaling messages. Before a dynamic PW is established between two PEs, an LDP session must be established between the two PEs. During the establishment of a dynamic PW, the label distribution mode is downstream unsolicited (DU) and the label retention mode is liberal label retention.

    NOTE:

    If Ps exist between the two PEs, the LDP session must be established in remote mode. If the two PEs are directly connected, the LDP session must be established in local mode.

    After PWE3 is configured on the two PEs and an LDP session is established between the two PEs, the dynamic PW starts to be established. Figure 6-7 shows the process of establishing a dynamic PW.

    1. PE1 sends a Label Request message and a Label Mapping message to PE2.

    2. After receiving the Label Request message from PE1, PE2 sends a Label Mapping message to PE1.

    3. After receiving the Label Mapping message from PE1, PE2 determines whether its PW configurations are consistent with those on PE1. If its PW configurations such as the VC ID, VC type, MTU, and control word (CW) enabling status are consistent with those on PE1, PE2 sets the PW status to Up.

    4. After receiving the Label Mapping message from PE2, PE1 determines whether its PW configurations are consistent with those on PE2. If they are consistent, PE1 sets the PW status to Up. After that, a dynamic PW is established between PE1 and PE2.

    5. After the dynamic PW is established, PE1 and PE2 learn the status of each other by exchanging Notification messages.

    Figure 6-7 Process of establishing and maintaining an SS-PW

    If the AC interface of a PW is Down or the corresponding tunnel is Down, Martini and PWE3 use different processing mechanisms:

    • In Martini mode, the local PE sends a Label Withdraw packet to its peer to tear down the PW. After the AC interface or tunnel goes Up, another round of negotiation is required for the PEs to establish a PW.

    • In PWE3 mode, the local PE sends a Notification message to notify its peer that packets cannot be forwarded, but the PW is not torn down. When the AC interface or tunnel goes Up, the local PE sends a Notification message to notify its peer that packets can be forwarded.

      A PW is torn down only when PW configurations are deleted from the PEs or the LDP session is interrupted. Notification messages prevent repeated PW establishment and deletion caused by network flapping.

    Figure 6-8 Process of tearing down an SS-PW

    Figure 6-8 shows the process of tearing down an SS-PW:

    1. When PW configurations are deleted from PE1, PE1 withdraws its VC label and sends Label Withdraw and Label Release messages to PE2 in succession.
      NOTE:
      The Label Withdraw message instructs a PE to withdraw the VC label. The Label Release message is a response to the Label Withdraw message, instructing the PE that sends the Label Withdraw message to withdraw the VC label. To tear down the PW more quickly, PE1 sends the Label Withdraw and Label Release messages in succession.
    2. After receiving the Label Withdraw and Label Release messages from PE1, PE2 withdraws its VC label and sends a Label Release message to PE1.
    3. When PE1 receives the Label Release message from PE2, the PW is torn down.

    The difference between an SS-PW and an MS-PW is that one or more SPEs exist between the end PEs of an MS-PW. Figure 6-9 shows an example of an MS-PW between PE1 and PE2. The SPE connects the two PW segments between PE1 and PE2.

    During signaling negotiation, the SPE forwards to PE2 the parameters carried in the Label Mapping message sent by PE1 and forwards to PE1 the parameters carried in the Label Mapping message sent by PE2. After these parameters are negotiated to be consistent, the PW status becomes Up. The forwarding of Label Release, Label Withdraw, and Notification messages are similar to the forwarding of Label Mapping messages.

    Figure 6-9 Signaling interaction process for an MS-PW
  • Extensions on the PWE3 Control Plane

    The PWE3 control plane has the following extensions:

    • LDP signaling in Notification mode

      LDP signaling in Notification mode is used for status advertisement. The signaling is removed only when the PW configurations are deleted or the signaling is interrupted. This implementation requires fewer control packet exchanges and reduces the signaling cost. Note that LDP signaling in Notification mode is compatible with the original LDP mode and Martini mode.

    • Mechanism for negotiating packet fragmentation

    • Functions of detecting PW connectivity, such as VCCV and PW operation, administration and maintenance (OAM), which enable faster network convergence and enhance network reliability

  • Extensions on the PWE3 Data Plane

    The PWE3 data plane has the following extensions:

    • Real-time information expansion

    • Bandwidth, jitter, and delay assurance

    • Retransmission of disordered packets

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Updated: 2019-01-14

Document ID: EDOC1100058940

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