Hello everyone,
Today, I will introduce how to handle the problem that switches connecting to devices at the two ends cannot transparently transmit BPDUs.
Network Topology
Figure 1-1 Network where a layer2 protocol transparent failure occurs
Fault Description
An LLDP neighbor relationship cannot be established between SwitchA and SwitrchC for the transparently transmitting BPDUs failure of SwitchB.
Configuration Files
SwitchA
interface Vlanif20
ip address 1.1.1.1 255.255.255.0
interface Eth-Trunk100
interface Ethernet0/0/0/0
ip address 10.220.7.128 255.255.254.0
interface GigabitEthernet1/1/1/23
port link-type access
port default vlan 20
ip route-static 0.0.0.0 0.0.0.0 10.220.6.1
SwitchB
interface Vlanif20
ip address 1.1.1.2 255.255.255.0
interface Vlanif220
ip address 10.220.7.121 255.255.254.0
interface Ethernet0/0/23
port link-type access
port default vlan 20
l2protocol-tunnel lldp enable
interface Ethernet0/0/24
port link-type access
port default vlan 20
l2protocol-tunnel lldp enable
interface GigabitEthernet0/0/2
port link-type trunk
port trunk pvid vlan 220
undo port trunk allow-pass vlan 1
port trunk allow-pass vlan 220
ip route-static 0.0.0.0 0.0.0.0 10.220.6.1
SwitchC
vlan batch 20 103 220
interface Vlanif20
ip address 2.1.1.1 255.255.255.0
interface MEth0/0/1
ip address 10.220.7.122 255.255.254.0
interface GigabitEthernet0/0/24
port link-type access
port default vlan 20
ip route-static 0.0.0.0 0.0.0.0 10.220.6.1
ip route-static 1.1.1.0 255.255.255.0 2.1.1.2
Troubleshooting Location
Troubleshooting Procedure
Step 1. Check information about neighbors of the device.
Run the display lldp neighbor brief command to check the current LLDP neighbors between devices.
<SwitchA> display lldp neighbor brief
Local Intf Neighbor Dev Neighbor Intf Exptime(s)
GE1/1/1/23 SwitchB Ethernet0/0/24 103
<SwitchB> display lldp neighbor brief
Local Intf Neighbor Dev Neighbor Intf Exptime(s)
Ethernet0/0/23 SwitchA GE1/1/1/23 118
Ethernet0/0/24 SwitchC GE0/0/24 103
<SwitchC> display lldp neighbor brief
Local Intf Neighbor Dev Neighbor Intf Exptime(s)
GE0/0/24 SwitchB Ethernet0/0/24 113
As a result, the current SwitchB failed to transparently tranmit the LLDP BPDUs as configured.
Step 2. Check the SwitchB anout Layer 2 protocol packets that are transparently transmitted.
Run the display l2protocol-tunnel statistics command the statistics about Layer 2 protocol packets that are transparently transmitted on a specified interface.
<SwitchB> display l2protocol-tunnel statistics Ethernet 0/0/23 lldp
--------------------------------------------------------------------------------
Port Protocol Drop Input Output Drop
Threshold Packets Packets Packets
--------------------------------------------------------------------------------
Ethernet0/0/23 lldp 0 0 0 0
<SwitchB> display l2protocol-tunnel statistics Ethernet 0/0/24 lldp
--------------------------------------------------------------------------------
Port Protocol Drop Input Output Drop
Threshold Packets Packets Packets
--------------------------------------------------------------------------------
Ethernet0/0/24 lldp 0 0 0 0
The command output does not contain statistics about transparently transmitted LLDP DUs.
Step 3. Check the layer 2 protocol transparent transmission configuration of the SwitchB.
Run the display current-configuration to check the configuration of layer 2 protocol transparent transmission on the specified interfaces based on the chapter Configuring Interface-based Layer 2 Protocol Transparent Transmission:
l Check whether the group MAC function for the transparent transmission of LLDP DUs is enabled globally.
l Check whether Layer 2 protocol transparent transmission is enabled on the interfaces connecting SwitchB to SwitchA and SwitchC, respectively.
#
interface Ethernet0/0/23
port link-type access
port default vlan 20
l2protocol-tunnel lldp enable
#
interface Ethernet0/0/24
port link-type access
port default vlan 20
l2protocol-tunnel lldp enable
It is found that the group MAC function is disabled globally on SwitchB.
Solution
Enables the SwitchB to replace the multicast destination MAC address of Layer 2 protocol packets with a specified multicast MAC address. When configuring Layer 2 protocol transparent transmission, pay attention to the following precautions Configuring Layer 2 Protocol Transparent Transmission Mode.
[SwitchB] l2protocol-tunnel lldp group-mac 0100-0100-0100
After this function is enabled, run the display lldp neighbor brief command to check the current LLDP neighbors between devices, you can find that SwitchB can transparently transmit LLDP DUs.
<SwitchA> display lldp neighbor brief
Local Intf Neighbor Dev Neighbor Intf Exptime(s)
GE1/1/1/23 SwitchC GE0/0/24 103
<SwitchC> display lldp neighbor brief
Local Intf Neighbor Dev Neighbor Intf Exptime(s)
GE0/0/24 SwitchA GE1/1/1/23 112
Root Cause
The group MAC function for the transparent transmission of Layer 2 protocol packets is disabled globally on SwitchB.
That is all I want to share with you!
