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NE40E V800R010C10SPC500 Feature Description - System Monitor 01

This is NE40E V800R010C10SPC500 Feature Description - System Monitor
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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).
MPLS Ping/Tracert

MPLS Ping/Tracert

Overview

The MPLS 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, MPLS ping and tracert have been introduced to detect LSP errors and locate faulty nodes. MPLS ping is used to check link connectivity and host reachability on an MPLS network.

MPLS ping includes P2P MPLS ping and Point-to-Multipoint (P2MP) MPLS ping. In this document, MPLS ping refers to P2P MPLS ping unless otherwise specified.

Similar to a common ping or tracert mechanism, MPLS ping or MPLS tracert checks the LSP status by sending MPLS Echo Request and Reply messages. Both types of packets are UDP packets transmitted using UDP port 3503. The receive end uses the UDP port number to identify MPLS Echo Request and Reply messages.

An MPLS Echo Request message carries information about the forwarding equivalence class (FEC) for an LSP to be monitored. The MPLS Echo Request message is forwarded with other service packets of the same FEC along the LSP. This procedure enables the LSP connectivity to be monitored. In addition, Echo Request messages are transmitted to the destination using MPLS, whereas MPLS Echo Reply messages are transmitted to the source using IP.

To prevent the egress from forwarding a received MPLS Echo Request message to other nodes, set the destination address to 127.0.0.0/8 (the local loopback address) and the time to live (TTL) value to 1 in the IP header of the message.

MPLS Ping

MPLS ping process

Figure 5-1 MPLS network

In Figure 5-1, an LSP destined for Device D is configured on Device A. The MPLS ping process on Device A is as follows:

  1. Device A checks whether the LSP is established. If the LSP is a TE tunnel, Device A checks whether the tunnel interface is configured and the CR-LSP is established. If the LSP is not established, an error code is displayed, and the MPLS ping process ends. If the LSP has been established, the MPLS ping process continues.

  2. Device A constructs an MPLS Echo Request message, with destination IP address 127.0.0.0/8 and TTL value 1 in the IP header. Then, Device A adds an LSP label to the MPLS Echo Request message and sends the message to Device B.

  3. Transit nodes Device B and Device C forward this MPLS Echo Request message using MPLS.

    If either transit node fails to forward the MPLS Echo Request message, this message is discarded.

  4. If MPLS forwarding is successful, the MPLS Echo Request message reaches the egress Device D, and the Device D replies with an MPLS Echo Reply message to Device A.

MPLS Tracert

MPLS tracert process

In Figure 5-1, the MPLS tracert process of 4.4.4.4/32 on Device A is as follows:

  1. Device A checks whether the LSP exists. If it does not exist, an error code is returned and the MPLS tracert process ends. If it exists, the MPLS tracert process continues.

  2. Device A constructs an MPLS Echo Request message, with destination IP address 127.0.0.0/8 and TTL value 1 in the IP header. Then, Device A adds an LSP label (TTL value of the label is 1) to the MPLS Echo Request message and sends the message to Device B. Upon receipt, Device B determines that the TTL of the LSP label in the message has timed out so that it replies with an MPLS Echo Reply message. The message carries the destination UDP port equal to the source UDP port in the MPLS Echo Request message, and destination IP address equal to the source IP address of the MPLS Echo Request packet, and the TTL value of 255.

  3. Upon receipt, Device A sends an MPLS Echo Request message with the TTL value of 2. Device B then forwards the message using MPLS. Upon receipt, Device C determines that the TTL of the LSP label in the message has timed out so that it replies with an MPLS Echo Reply message.

  4. After receiving the MPLS Echo Reply message sent by Device C, Device A sends an MPLS Echo Request message with the TTL value of 3. Device C then forwards the packet using MPLS. Upon receipt, if Device D is the egress node, Device D replies with an MPLS Echo Reply message. Then Device A obtains information about all nodes on the path.

P2MP MPLS Ping

P2MP ping process

Figure 5-2 P2MP ping networking

On the network shown in Figure 5-2, a P2MP TE LSP is established on PE1. PE2, PE3, PE4, and P3-BUD are leaf nodes. The P2MP ping process from PE1 on the LSP is as follows:

  1. PE1 checks whether the LSP exists.

    • If the LSP does not exist, an error code is displayed, and the P2MP Ping process ends.
    • If the LSP exists, the P2MP ping process continues.
  2. PE1 constructs an MPLS Echo Request message, with destination IP address 127.0.0.0/8 and the TTL value of 1. Then PE1 adds an LSP label to the MPLS Echo Request message and sends the packet to P1 and P2 along the LSP.
  3. Transit nodes P1, P2 and P4 forward this MPLS Echo Request message using MPLS. P3, a bud node, forwards the MPLS Echo Request message and sends it to the CPU for processing. If either transit node fails to forward the MPLS Echo Request message, a node will send an MPLS Echo Reply message with an error code.
  4. After being forwarded successfully along the LSP, the MPLS Echo Request packet reaches the egresses: PE2, PE3, PE4, and P3-BUD. Each node replies with an MPLS Echo Reply message. Then PE1 obtains information about all nodes on the path.

SR-TE IPv4 Ping

On the network shown in Figure 5-3, PE1, P1, and P2 all support SR. An SR-TE tunnel is established between PE1 and PE2. The devices assign adjacency labels as follows:
  • PE1 assigns adjacency label 9001 to PE1-P1 adjacency.
  • P1 assigns adjacency label 9002 to P1-P2 adjacency.
  • P2 assigns adjacency label 9005 to P2-PE2 adjacency.
Figure 5-3 SR-TE ping and tracert
The process of initiating an SR-TE ping test from PE1 is as follows:
  1. PE1 initiates a ping test and checks whether the specified tunnel type is SR-TE.
    • If the specified tunnel type is not SR-TE, PE1 reports an error message indicating a tunnel type mismatch and stops the ping test.
    • If the specified tunnel type is SR-TE, the following operations are performed:
  2. PE1 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.
  3. PE1 forwards the packet to P1. P1 removes the outer label (9002) of the received packet and forwards the packet to P2.
  4. P2 removes the outer label (9005) of the received packet and forwards the packet to PE2 for processing.
  5. PE2 returns an MPLS Echo Reply packet to PE1.

SR-TE IPv4 Tracert

On the network shown in Figure 2, the process of initiating an SR-TE tracert test from PE1 is as follows:
  1. PE1 initiates a tracert test and checks whether the specified tunnel type is SR-TE.
    • If the specified tunnel type is not SR-TE, PE1 reports an error message indicating a tunnel type mismatch and stops the tracert test.
    • If the specified tunnel type is SR-TE, the following operations are performed:
  2. PE1 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.
  3. PE1 forwards the packet to P1. After receiving the packet, P1 determines whether the TTL-1 value in the outer label is 0.
    • If the TTL-1 value is 0, an MPLS TTL timeout occurs. P1 sends the packet to the Rx/Tx module for processing and returns an MPLS Echo Reply packet to PE1.
    • If the TTL-1 value is greater than 0, P1 removes the outer MPLS label of the packet, buffers the TTL-1 value, copies the value to the new outer MPLS label, searches the forwarding table for the outbound interface, and forwards the packet to P2.
  4. Similar to P1, P2 also 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. P2 sends the packet to the Rx/Tx module for processing and returns an MPLS Echo Reply packet to P1.
    • If the TTL-1 value is greater than 0, P2 removes the outer MPLS label of the packet, buffers the TTL-1 value, copies the value to the new outer MPLS label, searches the forwarding table for the outbound interface, and forwards the packet to PE2.
  5. P2 forwards the packet to PE2, and PE2 returns an MPLS Echo Reply packet to PE1.

SR-TE IPv6 Ping

In Figure 5-4, nodes A, D, G, and Z have SRv6 capabilities. An SRv6 tunnel is established between nodes A and Z.
Figure 5-4 SRv6-TE ping/tracert
Node A pings the SRv6 tunnel. The process is as follows:
  1. Node A constructs an IPv6 Echo Request packet that carries whole IPv6 link information <Z, G, D>. The IPv6 DA is set to node D. A searches the IPv6 routing table and forwards the packet to node B.
  2. SRv6-incapable node B cannot process this packet and searches the IPv6 routing table to transparently transmit the packet to node D.
  3. Upon receipt of the packet, node D finds that itself is the IPv6 DA. Node D updates the IPv6 DA and SL information and searches the IPv6 routing table to forward the packet to node F.
  4. SRv6-incapable node F processes the packet in the same way as node B.
  5. Upon receipt of the packet, node G finds that itself is the IPv6 DA and the SL is reduced to 0, indicating that node G is the penultimate node. Node G updates the IPv6 DA, deletes IPv6 link information <Z, G, D>, and searches the IPv6 routing table to send the packet to node Z.
  6. Upon receipt of the packet, node Z processes the received IPv6 packet and sends it to the host transceiver module for processing. Then, node Z returns an IPv6 Echo Reply packet to node A.
  7. Node A receives the IPv6 Echo Reply packet and generates SRv6 ping results. If node A does not receive IPv6 Echo Reply packets, the tracert operation fails.

SR-TE IPv6 Tracert

The tracert mechanism is similar to the ping mechanism. Tracert first sends a packet with the TTL value of 1. Each time a tracert packet is sent, the TTL increases by one. Tracert checks whether a network connection is reachable and where a fault occurs.

In Figure 1, node A initiates a tracert operation on an SRv6 tunnel. The process is as follows:
  1. Node A continuously constructs IPv6 Echo Request packets and forwards them to node D.
  2. Node D checks whether TTL-1 is 0:
    • If TTL-1 is 0, the packets are sent to the host transceiver for processing after the TTL times out.
    • If TTL-1 is greater than 0, node D updates the IPv6 DA and SL information, searches the IPv6 routing table, and forwards the packets to the next-hop node G.
  3. Node G processes them in the same way as D. G checks whether TTL-1 is 0:
    • If TTL-1 is 0, the packets are sent to the host transceiver for processing after the TTL times out.
    • If TTL-1 is greater than 0, node G updates the IPv6 DA and SL information, searches the IPv6 routing table, and forwards the packets to the next-hop node Z.
  4. After common IPv6 packets arrive at node Z, node Z sends the packet to the host transceiver for processing and returns IPv6 Echo Reply packets to node A.
  5. After node A receives IPv6 Echo Reply packets, it generates SRv6 tracert results. If node A does not receive IPv6 Echo Reply packets, the tracert operation fails.

SR-BE IPv4 Ping

On the network shown in Figure 5-5, PE1, P1, P2, and PE2 are all capable of SR. An SR LSP is established between PE1 and PE2.
Figure 5-5 SR-BE ping/tracert
The process of initiating an SR IPv4 ping test from PE1 is as follows:
  1. PE1 initiates a ping test and checks whether the specified tunnel type is SR-BE IPv4.
    • If the specified tunnel type is not SR-BE IPv4, PE1 reports an error message indicating a tunnel type mismatch and stops the ping test.
    • If the specified tunnel type is SR-BE IPv4, the following operations are performed:
  2. PE1 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.
  3. PE1 forwards the packet to P1. After receiving the packet, P1 swaps the outer MPLS label of the packet and forwards the packet to P2.
  4. Similar to P1, P2 swaps the outer MPLS label of the received packet and determines whether it is the penultimate hop. If yes, P2 removes the outer label and forwards the packet to PE2. PE2 sends the packet to the Rx/Tx module for processing.
  5. PE2 returns an MPLS Echo Reply packet to PE1 and generates the ping test result.

SR-BE IPv4 Tracert

On the network shown in Figure 1, the process of initiating an SR-BE IPv4 tracert test from PE1 is as follows:
  1. PE1 initiates a ping test and checks whether the specified tunnel type is SR-BE IPv4.
    • If the specified tunnel type is not SR-BE IPv4, PE1 reports an error message indicating a tunnel type mismatch and stops the tracert test.
    • If the specified tunnel type is SR-BE IPv4, the following operations are performed:
  2. PE1 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.
  3. PE1 forwards the packet to P1. After receiving the packet, P1 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. P1 sends the packet to the Rx/Tx module for processing and returns a reply packet to PE1.
    • If the TTL–1 value is greater than 0, P1 swaps the outer MPLS label of the packet, searches the forwarding table for the outbound interface, and forwards the packet to P2.
  4. Similar to P1, P2 also performs the following operations:
    • If the TTL–1 value is 0, an MPLS TTL timeout occurs. P2 sends the packet to the Rx/Tx module for processing and returns a reply packet to PE1.
    • If the TTL–1 value is greater than 0, P2 swaps the outer MPLS label of the received packet and determines whether it is the penultimate hop. If yes, P2 removes the outer label, searches the forwarding table for the outbound interface, and forwards the packet to PE2.
  5. PE2 sends the packet 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: 2019-01-03

Document ID: EDOC1100055050

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