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Knowledge Base

Wholesale user not receiving DHCP offer due to VLAN Priority mismatch

Publication Date:  2012-07-27  |   Views:  232  |   Downloads:  0  |   Author:  SU1001049078  |   Document ID:  EKB0000560547


Issue Description

Refers to Network-Diagram.png, ISP A offer wholesale service to operator B with service class BE (802.1P=0).
Operator CPE only permit packets with 8021P =0, packets with other 8021p value will be discarded.

ME60 provide L2 Access, scenario IPoEoVLAN.

Based on the requirements, all packets need to remark as 8021p=0 before sending to Operator B.
A new diffserv domain is defined and apply on ME60's outbound interface.

diffserv domain cos0
8021p-outbound af1 green map 0
8021p-outbound af2 green map 0
8021p-outbound af3 green map 0
8021p-outbound af4 green map 0
8021p-outbound ef green map 0
8021p-outbound cs6 green map 0
8021p-outbound cs7 green map 0

interface GigabitEthernet x/x/x
trust upstream cos0
trust 8021p

During network integration testing, found the user unable to get IP address from ME60.

Alarm Information


Handling Process

1. Packet Capture has perform to find the root cause. Two Capture point as shown in the diagram:

2. At Point 1, user has send multiple DHCP Discover, however does not get any DHCP Offer from ME60.

3. At Point 2, ME60 is receiving DHCP discover and also send DHCP Offer to the user. Check on the Priority bit, the 8021P value for DHCP offer (8021P=7).

4. From the Packet Capture, we found that the DHCP offer packet is not mapped to 0.

Root Cause

Operator subscribe service class BE and the CPE only permit packets with 8021P =0, packet with other 8021p value will be discarded.

ME60 as the DHCP Server. After the user passed the authentication, ME60 will assign a IP address to the users through DHCP offer. By default, application packet is marked with 8021P=7.

The 8021P for DHCP packet is not mapped to 0 at the outgoing interface. Hence , the DHCP Offer Packet was discarded at the inbound of the wholesale access equipments.


Command on the interface, trust upstream diffserv_domain only effective for the packets that passing through the ME60, packets that originated or generates by ME60 are not affected.

Using command "8021p 8021p-value" in the interface view, all the application packet will be remarked with the 8021P-value as configured before forward to the access users.

Sample Configuration:

interface GigabitEthernet 1/0/0
description ***
trust upstream ***
trust 8021p
8021p 2
access-type layer2-subscriber default-domain authentication ***
authentication-method bind