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A GRE Tunnel Established on an NE40E Is Displayed as Down on One Side and Up on the Other Side

Publication Date:  2019-04-11 Views:  34 Downloads:  0
Issue Description

A GRE tunnel is established between an NE40E and a China Unicom device. The GRE tunnel is displayed as down on the local end but up on the remote end. However, the ping operation between the two ends is successful, and routes can be properly forwarded.

Handling Process

Check that the tunnel interface is in the down state.

[11:33:55][ZNXJ-NE40]dis interface Tunnel 0/0/0
[11:33:56]Tunnel0/0/0 current state : DOWN (ifindex: 48)
[11:33:56]Line protocol current state : DOWN
[11:33:56]Description: Unicom-M2M-AR
[11:33:56]Route Port,The Maximum Transmit Unit is 1500
[11:33:56]Internet Address is
[11:33:56]Encapsulation is TUNNEL, loopback not set
[11:33:56]Tunnel source (LoopBack1), destination
[11:33:56]Tunnel protocol/transport GRE/IP, key disabled
[11:33:56]keepalive disabled
[11:33:56]Checksumming of packets disabled
[11:33:56]Current system time: 2018-01-05 11:33:59
[11:33:56]    300 seconds input rate 0 bits/sec, 0 packets/sec
[11:33:56]    300 seconds output rate 0 bits/sec, 0 packets/sec
[11:33:56]    0 seconds input rate 0 bits/sec, 0 packets/sec
[11:33:56]    0 seconds output rate 0 bits/sec, 0 packets/sec
[11:33:56]    0 packets input,  0 bytes
[11:33:56]    0 input error
[11:33:56]    0 packets output,  0 bytes
[11:33:56]    0 output error
[11:33:56]    Input:
[11:33:56]      Unicast: 0 packets, Multicast: 0 packets
[11:33:56]    Output:
[11:33:56]      Unicast: 0 packets, Multicast: 0 packets
[11:33:56]    Input bandwidth utilization  :    0%
[11:33:56]    Output bandwidth utilization :    0%


Check that the loopback interface is up.

[NE40-Tunnel0/0/0]dis ip int br
*down: administratively down
!down: FIB overload down
^down: standby
(l): loopback
(s): spoofing
(d): Dampening Suppressed
(E): E-Trunk down
The number of interface that is UP in Physical is 6
The number of interface that is DOWN in Physical is 20
The number of interface that is UP in Protocol is 4
The number of interface that is DOWN in Protocol is 22

Interface                         IP Address/Mask      Physical   Protocol VPN
GigabitEthernet0/0/0           down       down     l3vpn
LoopBack1                     up         up(s)    -- 


Check that the following configurations are correct.

[NE40-Tunnel0/0/0]dis this
interface Tunnel0/0/0
 description Unicom-M2M-AR
 ip address
 tunnel-protocol gre
 source LoopBack1

 interface LoopBack1
 description GRE_Source
 ip address
 target-board 1
 binding tunnel gre

It is found that the source interface of the GRE tunnel is on the board in slot 1.

After the tunnel interface name is changed to Tunnel 1/0/0, the GRE tunnel becomes up.
Run the target-board command to configure mapping between layer 3 interfaces and the tunnel service board.
The target-board slot-number parameter specifies the slot ID of the service board of the GRE tunnel.

Root Cause

The three-dimensional interface Tunnel 1/x/x indicates that the interface board is in slot 1. The slot ID and the tunnel ID do not match.


Change the tunnel interface name to Tunnel 1/0/0.


Three-dimensional tunnel interfaces are used in centralized GRE mode. To allow packet transmission over GRE tunnels in centralized GRE mode, the mapping between the source tunnel interface and the tunnel service board must be configured, and the target-board command needs to be run to bind the interface to the GRE protocol. In this case, the packets can be sent to the associated tunnel service board for processing only when they are over the GRE tunnel that uses the interface's IP address as the source IP address. The target-board slot-number command applies only to the centralized GRE mode.
In centralized GRE mode, the target-board slot-number command is a prerequisite of running the binding tunnel gre command to bind an interface to the GRE protocol. The slot number specified in the target-board command must be the same as x in the interface name x/y/z.