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Knowledge Base

Since VLAN priority of PODI and PADO are inconsistent PPPOE failed

Publication Date:  2019-07-04  |   Views:  396  |   Downloads:  0  |   Author:  90006129  |   Document ID:  ETC0002805747


Issue Description

Problem description :  the PPPoE session failed to build.

Network:  CPE ---> OLT ---> Metor Netowrk --> BRAS --> IPBB --> Internet

Software verison: ME60 V6R8C00

Handling Process

1. Open the debugging,found ME60 received PODA message and responded PADO message, but didn't found PADR and PADS message.

2. Captured the packets at ME60 BAS interface, found the VLAN priority of PADI packets receiving from OLT is 0. 

3. Discreet message on OLT and capture the packets ,found some message are dropped at OLT user interface.

4. Knew from the OLT configuration, OLT set VLAN priority 0.  

5. Whenever in default ME60 put the VLAN priority 7 

Root Cause

1.     The CPE send a PADI packet for discovery with VLAN priority 0. It passes.

2.     In default, ME60 responds with PADO with VLAN priority 7. And it is dropped by OLT.


<!--[if !supportLists]-->1.   Configure ‘trust 8021p-protocol’ under BAS interface on ME60. It will inherit the incoming priority of the Request packet (such as PADI) and send the response with the same priority.

<!--[if !supportLists]-->2.   Nothing to be done for the data packets. ME60 will tag 8021p with 0 by default no matter what the IP ToS (or DSCP) is.


<!--[if !supportLists]-->1. The subscribers need QoS for different services. A PC can apply all kinds of applications, including Internet surfing, real-time gaming, Video and Voice. Different services have different requirements for QoS when a congestion happens. Differentiated-service mode of QoS is based on different priorities. In a word, the end subscribers need different priorities.

<!--[if !supportLists]-->2.   CPEs and end subscribers care about IP priority instead of VLAN priority. There are 2 priorities here: VLAN priority (as known as 8021p) and IP priority (as known as IP ToS or DSCP). The VLAN priority will be stripped off at CPEs. So the priority that end subscribers care is the IP priority instead of VLAN priority.

<!--[if !supportLists]-->3.   According to the previous investigation, the OLTs of Metro network only allows VLAN priority 0, but it doesn’t check IP priority. So, for an IP packet with both IP priority and VLAN priority, whatever the IP priority is, it can pass with the VLAN priority 0. For a non-IP packet, such as PPPoE packet (esp. PADO) and ARP packet, to set the VLAN priority to 0 is OK.

For ME60:

Suggest in defaul ME60 inherit the incoming priority of the Request packet (such as PADI) and send the response with the same priority.