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Ping Fails Because the 802.1 p Priority Configuration Is Incorrect in the ICMP Message

Publication Date:  2013-01-07 Views:  21 Downloads:  0
Issue Description

 

NE80E-2 is deployed in VPLS networking. A user packet is sent from Router to NE80E-2. There are three layers of VLANs on NE80E-2. NE80E-2 sends the user packet based on VPLS forwarding to the ME60, with two VLAN tags removed and one VLAN tag left. Router processes a packet only when the packet's priority is 1.

The symptoms are as follows:

NE80E-1 cannot ping Router.

The ME60 can ping Router.

Handling Process

The on-site Huawei technical support personnel use NE80E-1 to ping Router and capture the ICMP messages on the outbound interface on NE80E-2. Information about the ICMP messages is as follows.

 

The captured ICMP messages carry three VLAN tags, with the most inner VLAN tag carrying the priority 1 and the other two VLAN tags carrying the priority 0.

They use the ME60 to ping Router and capture the ICMP messages on the outbound interface on NE80E-2. Information about the ICMP messages is as follows.

 

The captured ICMP messages carry three VLAN tags, with the most inner VLAN tag carrying the priority 0 and the other two VLAN tags carrying the priority 1. The ping result shows that the ME60 can ping Router successfully while NE80E-1 fails to ping Router. Based on the packet analysis, the ping failure of NE80E-1 results from the priority of 0 in the outer VLAN tag.

They check the configurations on NE80E-2.

 

When a packet entering NE80E-2 carries only one VLAN tag and the VLAN priority is 1, the packet does not match the traffic policy. Because the trust upstream qinq and trust 8021p commands are configured on the interface, the packet sent by NE80E-2 must have the priority of the inner VLAN tag mapped to the priority of the outer VLAN tag.

However, when the packet entering NE80E-2 carries only one VLAN tag and the VLAN priority is 0, the packet matches the traffic policy. Then the packet has the the priority of the inner VLAN tag mapped to the priority of the outer VLAN tag based on the traffic behavior. The result of the ME60 pinging Router shows that the ICMP messages have the priorities of the inner VLAN tags mapped to the priorities of the outer VLAN tags after the ICMP messages match the traffic policy.

Therefore, the ME60 can ping Router successfully. When the ICMP messages do not match the traffic policy, the configurations of the trust upstream qinq and trust 8021p commands are incorrect, causing the priority of the inner VLAN tag to fail to be mapped. As a result, NE80E-1 fails to ping Router.

Then they analyze the reason why the priority of the VLAN tag carried in an ICMP message sent from NE80E-1 to NE80E-2 is 1 while the priority of the VLAN tag carried in an ICMP message sent from the ME60 to NE80E-2 is 0. They check the ME60 configuration and find that a traffic policy is applied to the outbound interface on the ME60.

As a result, the priorities of the VLAN tags carried in all sent ICMP messages are mapped to 1. In this case, all ICMP messages sent by NE80E-1 are forwarded through the ME60, and the priorities of their VLAN tags are changed to 1. However, the traffic policy on the ME60 does not affect the ICMP messages that the ME60 sends. Therefore, the priorities of their VLAN tags are 0.

Root Cause

The trust 8021p command does not meet the requirements of Router.

Solution

Change the traffic policy on NE80E-2 to enable all ICMP messages reaching NE80E-2 to match the traffic policy. An example configuration is shown as follows.


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