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NE20E-S2 V800R010C10SPC500 Feature Description - System Monitor 01

This is NE20E-S2 V800R010C10SPC500 Feature Description - System Monitor
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EVPN VPWS Ping/Tracert

EVPN VPWS Ping/Tracert

Overview

The EVPN VPWS control plane establishes label switched paths (LSPs) but it cannot detect data forwarding failures in LSPs, which causes network maintenance difficulties. To address this issue, EVPN VPWS ping/tracert has been introduced to detect EVPN VPWS tunnel errors and locate failure nodes.

Similar to a common ping mechanism, EVPN VPWS ping checks EVPN VPWS connectivity by sending EVPN VPWS echo request and EVPN VPWS echo reply messages. Both types of packets are UDP packets transmitted using port 3503. The receive end uses the UDP port number to identify EVPN VPWS echo request and reply packets.

An EVPN VPWS echo request message carries information about the forwarding equivalence class (FEC) for an EVPN VPWS tunnel to be monitored. The EVPN VPWS echo request message is forwarded with other service packets of the same FEC along the EVPN VPWS tunnel. This procedure enables EVPN VPWS connectivity check. In addition, EVPN VPWS echo request messages are transmitted to the destination using EVPN VPWS tunnels, whereas EVPN VPWS echo reply messages are transmitted to the source using IP.

NOTE:
Currently, EVPN VPWS ping/tracert supports only the MPLS public network. The MPLS public network tunnels that can bear EVPN VPWS tunnels include the LDP, TE, BGP LSP, SR-TE, and SR-BE.

EVPN VPWS Ping

Figure 5-16 EVPN VPWS network

In Figure 5-16, CE1 and CE2 are user access devices directly connected to the MPLS network. The process of initiating an EVPN VPWS ping test from PE1 is as follows:

  1. PE1 initiates a test to check whether the tunnel between a specified source EVPN VPWS ID and a specified destination EVPN VPWS ID exists.

    • If the tunnel does not exist, PE1 reports an error message indicating that the tunnel does not exist and stops the ping test.
    • If the tunnel exists, PE1 continues the ping operation.
  2. PE1 uses the source EVPN VPWS ID and destination EVPN VPWS ID to subscribe to VPWS tunnel information, and constructs an MPLS echo request packet encapsulating the outer label of the initiator and carrying destination address 127.0.0.0/8 in the IP header of the packet, and sends the packet to the P.

  3. P swaps the outer MPLS label of the received packet and determines whether it is the penultimate hop. If yes, P removes the outer label and forwards the packet to PE2. PE2 sends the packet to the Rx/Tx module for processing.

  4. PE2 returns an MPLS echo reply packet to PE1 and generates the ping test result.

EVPN VPWS Tracert

Figure 5-16 shows the process of initiating an EVPN VPWS tracert test from PE1.

  1. PE1 initiates a test to check whether the tunnel between a specified source EVPN VPWS ID and a specified destination EVPN VPWS ID exists.

    • If the tunnel does not exist, PE1 reports an error message indicating that the tunnel does not exist and stops the tracert test.
    • If the tunnel exists, PE1 continues the tracert operation.
  2. PE1 uses the source EVPN VPWS ID and destination EVPN VPWS ID to subscribe to VPWS tunnel information and next-hop information based on the tunnel type, constructs an MPLS echo request packet encapsulating label information about the entire tunnel and carrying destination address 127.0.0.0/8 in the IP header of the packet, and sends the packet to the P.

  3. After receiving the MPLS echo request packet, P determines whether the TTL–1 value in the outer label of the received packet is 0.
    • If the TTL-1 value is 0, an MPLS TTL timeout occurs. P sends the packet to the Rx/Tx module for processing.

    • If the TTL-1 value is greater than 0, P swaps the outer MPLS label of the packet, searches the forwarding table for the outbound interface, and forwards the packet to PE2.

  4. After receiving the packet, PE2 sends it to the Rx/Tx module for processing, returns an MPLS echo reply packet to PE1, and generates the tracert test result.
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Updated: 2019-01-02

Document ID: EDOC1100055478

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