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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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Huawei uses machine translation combined with human proofreading to translate this document to different languages in order to help you better understand the content of this document. Note: Even the most advanced machine translation cannot match the quality of professional translators. Huawei shall not bear any responsibility for translation accuracy and it is recommended that you refer to the English document (a link for which has been provided).
Packet Encapsulation

Packet Encapsulation

Packet Encapsulation on ACs

Packet encapsulation on ACs depends on the user access mode, which can be VLAN or Ethernet access. The default user access mode is VLAN access.

Table 6-2 Packet encapsulation on ACs

Packet Encapsulation Type

Description

VLAN

The header of each Ethernet frame sent between CEs and PEs carries a VLAN tag, known as the provider-tag (P-Tag). This is a service delimiter identifying users on an ISP network.

Ethernet

The header of each Ethernet frame sent between CEs and PEs does not carry a P-Tag. If the frame header contains a VLAN tag, it is an inner VLAN tag called the user-tag (U-Tag). A CE does not add the U-Tag to an Ethernet frame; instead, the tag is carried in a packet before the packet is sent to the CE. A U-Tag informs the CE to which VLAN the packet belongs, and is meaningless to PEs.

Packet Encapsulation on PWs

The PW ID and PW encapsulation type uniquely identify a PW. The PW IDs and PW encapsulation types configured on the two end PEs of a PW must be the same. The packet encapsulation types of packets on PWs can be raw or tagged. By default, packets on PWs are encapsulated in tagged mode.

Table 6-3 Packet encapsulation on PWs

Packet Encapsulation Type

Description

Raw

Packets transmitted over a PW cannot carry P-Tags. If a PE receives a packet with the P-Tag from a CE, the PE strips the P-Tag and adds double labels (outer tunnel label and inner VC label) to the packet before forwarding it. If a PE receives a packet with no P-Tag from a CE, the PE directly adds double labels (outer tunnel label and inner VC label) to the packet before forwarding it. The PE determines whether to add the P-Tag to a packet based on actual configurations before sending it to a CE. The PE is not allowed to rewrite or remove an existing U-Tag.

Tagged

Packets transmitted over a PW must carry P-Tags. If a PE receives a packet with the P-Tag from a CE, the PE directly adds double labels (outer tunnel label and inner VC label) to the packet before forwarding it. If a PE receives a packet with no P-Tag from a CE, the PE adds a null P-Tag and double labels (outer tunnel label and inner VC label) to the packet before forwarding it. The PE determines whether to rewrite, remove, or preserve the P-Tag of a packet based on actual configurations before forwarding it to a CE.

VPLS Packets and Encapsulation Modes

Encapsulation modes of packets transmitted over ACs and PWs can be used together. The following uses Ethernet+raw encapsulation (without the U-Tag) and VLAN+tagged encapsulation (with the U-Tag) as examples to describe the packet exchange process.

  • Ethernet+raw encapsulation (without the U-Tag)

    Figure 6-6 Ethernet+raw encapsulation (without the U-Tag)

    As shown in Figure 6-6, ACs use Ethernet encapsulation and PWs use raw encapsulation; packets transmitted from CEs to PEs do not carry U-Tags.

    The packet exchange process is as follows:

    1. CE1 sends a Layer 2 packet without a U-Tag or P-Tag to PE1.

    2. PE1 searches the corresponding VSI for a forwarding entry and selects a tunnel and a PW to forward the packet based on the found forwarding entry.

    3. PE2 receives the packet from PE1 and decapsulates the packet by removing the Layer 2 encapsulation header added by PE1 and the inner VC label of the packet (the outer tunnel label has been popped out at the penultimate hop).

    4. PE2 sends the original Layer 2 packet to CE2.

    The processing of sending a packet from CE2 to CE1 is similar to this process.

  • VLAN+tagged encapsulation (with the U-Tag)

    Figure 6-7 VLAN access in tagged mode (with the U-Tag)

    As shown in Figure 6-7, ACs use VLAN encapsulation and PWs use tagged encapsulation; packets transmitted from CEs to PEs carry U-Tags and P-Tags.

    The packet exchange process is as follows:

    1. CE1 sends a packet that has Layer 2 encapsulation and carries both a U-Tag and a P-Tag to PE1.

    2. Upon receipt, PE1 does not process the two tags (PE1 retains the U-Tag because it treats the U-tag service data.

    3. PE1 retains the P-Tag because a packet sent to a PW with the tagged packet encapsulation mode must carry a P-Tag).
    4. PE1 searches the corresponding VSI for a forwarding entry and selects a tunnel and a PW to forward the packet based on the found forwarding entry.
    5. PE1 adds double labels (outer tunnel label and inner VC label) to the packet based on the selected tunnel and PW, performs Layer 2 encapsulation, and forwards the packet to PE2.
    6. PE2 receives the packet from PE1 and decapsulates the packet by removing the Layer 2 encapsulation header added by PE1 and the inner VC label of the packet (the outer tunnel label has been popped out at the penultimate hop).

    7. PE2 forwards the original Layer 2 packet to CE2. The packet carries the U-Tag and P-Tag.

    The processing of sending a packet from CE2 to CE1 is similar to this process.

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Updated: 2019-04-03

Document ID: EDOC1100075353

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