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AR Router Troubleshooting Guide

This Product Documentation provides guidance for maintaining AR Enterprise Router, covering common information collection and fault diagnostic commands, typical fault troubleshooting guide, and troubleshooting.
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What Are the Causes for a GRE Tunnel Establishment Failure?

What Are the Causes for a GRE Tunnel Establishment Failure?

Possible Causes

  • Interfaces on both ends of a tunnel use different tunnel encapsulation modes.

  • No IP address, tunnel source address, or tunnel destination address is configured for interfaces on both ends of the tunnel. The source address of one end is not the destination address of the other end.

  • GRE key configurations on both ends of the tunnel are inconsistent.

  • There is no reachable route between the tunnel source and destination addresses.

  • The configuration of the Keepalive function and the number of transmitted and received Keepalive packets are incorrect on the interfaces at both ends of the tunnel.

  • Different MTU values are set on the two ends of the tunnel.

  • The TCP MSS value is incorrectly set on an interface. Ensure that the total packet length (TCP MSS plus all the header lengths) is no greater than the MTU value. Otherwise, packets may not be transmitted correctly.

Troubleshooting Procedure

  1. Run the display this command on each tunnel interface to check the basic configuration. Correct any misconfigurations.

    For example, run the tunnel-protocol command on each tunnel interface to set the tunnel protocol to GRE. Ensure that the same tunnel protocol is configured for the two tunnel interfaces. Run the source and destination commands set to the destination address of the local tunnel interface to the source address of the remote tunnel interface and set the source address of the local tunnel interface to the destination address of the remote tunnel interface. If the keyword for identifying the GRE tunnel is set using the gre key command, ensure that the keywords are consistent on both ends of the tunnel.

    [Huawei-Tunnel0/0/0] display this 
    [V200R009C00SPC300] 
    # 
    interface Tunnel0/0/0 
     ip address 172.16.1.1 255.255.255.252 
     tunnel-protocol gre 
     source GigabitEthernet1/0/0 
     destination 1.1.1.2 
    # 
    return 
  2. Run the display ip routing-table command to check whether routes to the destination address of the tunnel interface are correct.

    If no routes to the destination address are displayed, run the ip route-static command to add such routes or manually advertise routes to the destination network segment on neighbors running the related dynamic routing protocol. The GRE tunnel status alternates between up and down if the outbound interface in the routes to the destination address of the tunnel interface is the local tunnel interface, or the neighbor device may advertise an incorrect route. To resolve the problems, configure a 32-bit static route with high priority.

    After confirming that the routes to the destination address of the GRE tunnel interface are correct, run the display ip interface brief command to check whether the tunnel interface is in Up state.

  3. Run the display this command on each GRE tunnel interface to check whether the Keepalive function is configured.

    • If the Keepalive function is configured on the tunnel interface, run the display keepalive packets count command on the interface to view the number of transmitted and received Keepalive packets and the number of received Keepalive response packets.

      The Keepalive function takes effect unidirectionally. To enable the Keepalive function on both ends of a tunnel, run the keepalive command on both ends of the tunnel. The Keepalive configuration takes effect on one end even if the function is disabled on the other end. By default, the interval for sending Keepalive packets is 5 seconds, and the retransmission count is 3. If an end does not receive Keepalive packets from the other end within 15 consecutive seconds, the tunnel goes down.

    • If the number of Keepalive packets sent by the local end is greater than the number of Keepalive response packets received from the remote end, packet loss occurs during transmission. If this occurs, check the link and the remote end.

    • If the statistics on the local end show that the number of received Keepalive packets is greater than the number of transmitted Keepalive response packets, the local end may fail to respond to Keepalive packets.

  4. Run the ping -s packetsize -a source-ip-address host command to check whether packets are fragmented.

    Run the ping command to test packets of different sizes and determine whether packet loss occurs or the ping fails. Find the threshold (If the packet size exceeds the threshold, packets may be lost or the ping may fail.)

    Run the mtu mtu command in the interface view to change the MTU value to be less than the threshold.

    If the access speed of some TCP services remains low or if some TCP services are interrupted intermittently after a new MTU value is configured, run the tcp adjust-mss value command in the interface view to change the MSS value of TCP packets.

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Updated: 2019-05-10

Document ID: EDOC1000079719

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