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CLI-based Configuration Guide - VPN

AR100, AR120, AR150, AR160, AR200, AR1200, AR2200, AR3200, and AR3600 V200R010

This document describes VPN features on the device and provides configuration procedures and configuration examples.
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VLL Modes

VLL Modes

VLL in CCC Mode

Introduction

A VLL connection in Circuit Cross Connect (CCC) mode is set up through the static configuration.

A CCC connection does not require signaling negotiation or exchange of control packets; therefore, it consumes few resources and is easy to configure. This mode applies to small MPLS networks with simple topologies.

Topology

The CCC mode supports both local and remote connections. Figure 10-3 shows the topology in CCC mode.

NOTE:

Currently, the device does not support remote CCC connection.

Figure 10-3  CCC connections

Local connection: Site1 and Site2 of VPN2 are connected through a CCC local connection (the black dashed line). PE3 acts as a Layer 2 switch for Site1 and Site2, and no LSP is required between the CE devices connected to PE3.

Remote connection: Site1 and Site2 of VPN1 are connected through a CCC remote connection (the blue dashed line). Site1 and Site2 require two static LSPs: one from PE1 to PE2 and one from PE2 to PE1. The two blue dashed lines represent a bidirectional PW, or CCC remote connection. This CCC remote connection is similar to a traditional L2VPN connection.

A CCC remote connection uses static VCs and maps L2PDUs received on one end of a VC to a static LSP. The L2PDUs are forwarded along the static LSP hop by hop based on the MPLS configuration and finally reach the other end of the VC. Unlike other VLL modes, the CCC mode uses a single label to transmit data. This label is swapped on each label switching router (LSR). Therefore, each LSP is used exclusively, and two LSPs in forward and reverse directions must be configured for each CCC connection. The LSPs associated with a CCC connection can transmit only the data of this connection and cannot be used for other MPLS L2VPN connections. In addition, the LSPs cannot be used to set up a BGP/MPLS IP VPN connection or transmit common IP packets.

VLL in Martini Mode

Introduction

VLL in Martini mode uses the Label Distribution Protocol (LDP) as the signaling protocol to transmit VC information. It complies with RFC4906 and extends LDP by adding a forwarding equivalence class (FEC), VC FEC, for VC label switching. A PE device assigns a VC label to each connection between CE devices. VC labels are carried in L2VPN information and forwarded to a remote PE device through an LDP LSP over the public network. As VLL connections are identified using VC labels, and multiple VC LSPs can be created on an LSP on the public network. The mappings between VC labels and LSPs are saved only on PE devices, while the P devices do not need to maintain any L2VPN information. Therefore, Martini mode is highly scalable. Additionally, it allows multiple VLL connections to use the same public tunnel, which is not supported by the CCC mode.

In Martini mode, a VC is identified by its VC type and VC ID.

  • VC type: indicates the encapsulation type of a VC, VLAN encapsulation or Ethernet encapsulation.

  • VC ID: identifies a VC. VCs of the same type must have different VC IDs on a PE device.

Topology

VLL in Martini mode supports only remote connections. Figure 10-4 shows the topology in Martini mode.

Figure 10-4  Topology in Martini mode
Implementation

Martini implementation involves VLL establishment and VLL packet forwarding. PW establishment is key to VLL establishment. As long as a PW is established, packets can be forwarded.

  1. PW Establishment and Teardown
  2. Packet Forwarding

The Martini mode uses extended LDP to exchange VC labels. For details about LDP, see VC Information Exchange.

PW Establishment and Teardown

  • Establishing a PW

    The downstream unsolicited (DU) label distribution mode and liberal label retention mode are used to establish a PW. For details, see LDP LSP Establishment in the MPLS Configuration.

    Figure 10-5  Establishing a PW using LDP

    After an LDP session is established between the PE devices, a PW is established in the process shown in Figure 10-5.

    1. PE1 sends a Request packet to PE2 and sends a Label Mapping message to PE2 in DU mode. The Label Mapping message carries information including the VC label, VC type, VC ID, and interface parameters.

    2. After PE2 receives the Request packet, it sends a Label Mapping message to PE1. After PE2 receives the Label Mapping message, it compares VC information carried in the message with its own VC information. If they are the same, PE1 and PE2 are in the same VLL. PE2 then accepts the Label Mapping message, and a unidirectional VC1 is established. PE2 knows the inner VC label that it needs to add to packets to sent the packets to PE1.

    3. After PE1 receives the Label Mapping message from PE2, it processes the message in the same way to establish VC2 in the reverse direction. The two unidirectional VCs constitute a PW.

  • Tearing down a PW

    Figure 10-6  Tearing down a PW using LDP

    When the AC or tunnel goes Down or a VC is deleted, the PW is torn down. Figure 10-6 shows the process of tearing down a PW.

    1. When PE1 detects that the AC or tunnel has gone Down or a VC has been deleted, it sends a Withdraw message to PE2 to instruct PE2 to delete the VC label. To tear down the PW more quickly, PE1 sends a Withdraw message and a Release message consecutively. The Release message notifies PE2 that PE1 has deleted the VC label.

    2. After receiving the Withdraw and Release messages, PE2 deletes the VC1 label and tears down VC1. PE2 then sends a Release message to PE1 to instruct PE1 to delete the VC2 label.

    3. After receiving the Release message, PE1 deletes the VC2 label and tears down VC2. Then the PW is torn down.

Packet Forwarding

A VLL is established after VC information exchange and PW establishment. The following describes the packet forwarding process in Martini mode.(This figure shows two VLL networks: VPN1 and VPN2.)

Figure 10-7  Packet forwarding process in Martini mode

Figure 10-7 shows packet forwarding in two directions: from Site1 to Site2 and from Site2 to Site1.

  • From Site1 to Site2

    When a packet of VLAN 10 is sent from Site1 of VPN1 to PE1, PE1 adds a VC label 3000 and an outbound label 1000 of LSP1 to the packet. Then the packet enters LSP1 (the black dashed line). When a packet of VLAN 100 is sent from Site1 of VPN2 to PE1, PE1 adds a VC label 4000 and an outbound label 1000 of LSP1 to the packet. Then the packet enters LSP1 (the black dashed line).

    When packets sent from Site1 reach PE2, PE2 removes the inbound label 1002 of LSP1 and selects the outbound interface according to the inner VC label. If the inner VC label is 3000, PE2 forwards the packets to the outbound interface connected to Site2 of VPN1. If the inner VC label is 4000, PE2 forwards the packets to the outbound interface connected to Site2 of VPN2. PE2 transmits VC labels 3000 and 4000 to PE1 using LDP when they set up the VCs.

  • From Site2 to Site1

    When a packet of VLAN 10 is sent from Site2 of VPN1 to PE2, PE2 adds a VC label 3500 and an outbound label 2000 of LSP2 to the packet. Then the packet enters LSP2 (the blue dashed line). When a packet of VLAN 100 is sent from Site2 of VPN2 to PE2, PE2 adds a VC label 4500 and an outbound label 2000 of LSP2 to the packet. Then the packet enters LSP2 (the blue dashed line).

    When packets sent from Site2 reach PE1, PE1 removes the inbound label 2002 of LSP2 and selects the outbound interface according to the inner VC label. If the inner VC label is 3500, PE1 forwards the packets to the outbound interface connected to Site1 of VPN1. If the inner VC label is 4500, PE1 forwards the packets to the outbound interface connected to Site1 of VPN2. PE1 transmits VC labels 3500 and 4500 to PE2 using LDP when they set up the VCs.

In the transmission process, the outer labels specify the LSP for data transmission on the ISP network, and the inner VC labels identify data from different users. Data from multiple VCs can be transmitted over the same LSP.

To deploy VLL in Martini mode, the ISP network must be able to automatically set up LSPs. Therefore, the ISP network must support MPLS forwarding and MPLS LDP. If the ISP network does not support LDP, GRE tunnels can be used on the ISP network.

VC Information Exchange

The Martini VLL extends the standard LDP by adding a VC FEC (type 128) to a Label Mapping message to carry VC information during PW establishment.

Figure 10-8 shows the format of a Label Mapping message. You can see the VC FEC in the Label Mapping message.

Figure 10-8  LDP Label Mapping message

VC FEC contains the inner VC label and interface parameters.

Table 10-4  Description of fields in the VC FEC (Type 128)

Field

Description

Bits

Remarks

VC TLV

Type, Length, and Value (TLV) of a VC

8

The value is 0x80, or 128 in decimal notation.

C

Control word

1

If the value is 1, control word is supported. If the value is 0, control word is not supported.

VC Type

Type of a VC

15

The value can be Ethernet or VLAN.

VC Info Length

Length of VC information

8

The value is the total length of the VC ID and the Interface Parameters field.

Group ID

ID of a VC group

32

Multiple VCs can constitute a VC group and information about all VCs in the group can be deleted together.

VC ID

ID of a VC

32

-

Interface Parameters

Interface parameters

Variable, smaller than the value of VC Info Length

The frequently used interface parameters include MTU and interface description.

VLL in SVC Mode

Introduction

The static virtual circuit (SVC) mode is a simplified Martini mode. Unlike the Martini mode that uses LDP to exchange VC labels, the SVC mode uses VC labels that are manually configured on PE devices.

An SVC VLL uses static VC labels and does not need VC label mapping. Therefore, LDP is not required for transmitting VC labels.

Topology

The SVC mode sets up a public tunnel (outer label) in the same way as the Martini mode. The inner label is manually configured during VC setup, and PE devices do not need to exchange VC labels using any signaling protocol. The SVC mode does not support local connections. The network topology and packet exchange process in SVC mode are the same as those in Martini mode.

Figure 10-9  Packet exchange in SVC mode

As shown in Figure 10-9, an SVC VLL is established between two sites of VPN1. On PE1, the label for sent packets is set to 4000 and the label for received packets is set to 3500. On PE2, the label for sent packets is set to 3500 and the label for received packets is set to 4000. When a packet is sent from Site1 to Site2 of VPN1, PE1 adds the inner VC label 4000 to the packet. After PE2 receives the packet with the inner VC label 4000, it sends the packet to the CE device through the AC mapping the inner VC label.

Comparison of VLL Modes

Table 10-5 compares three VLL modes.

Table 10-5  Comparison of VLL modes

Implementation

VC Label Distribution Mode

PW Signaling Protocol

Characteristics

CCC

Manually specified

None

This mode establishes one-layer static LSP tunnels for VC information transmission.

Martini

Randomly distributed by the system

LDP

This mode establishes two layers of tunnels. The outer tunnel is a public network tunnel used to transparently transmit data, and the inner tunnels are identified by VC labels distributed by the system.

SVC

Manually specified

None

This mode establishes two layers of tunnels. The outer tunnel is a public network tunnel used to transparently transmit data, and the inner tunnels are identified by VC labels that are manually specified.

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Updated: 2019-08-07

Document ID: EDOC1100033725

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