STB ------ MSAN ------ (METRO-E) ------ ME60(DHCP Relay) ------ DHCP Server
Possible causes for such a problem are as follows:
1. The DHCP server does not respond to user's request.
2. The DHCP relay device does not forward the response packets from the DHCP server.
3. The DHCP relay device does not forward user's requests.
To address the issue, Huawei performed the following operations and observed the following information:
1. Checked the packet statistics on the DHCP relay device.
<BSRTRM01>display dhcp relay statistics
Bad Packets recieved: 0
DHCP packets received from clients: 35
DHCP DISCOVER packets received: 35 --- (The DHCP relay device received DHCP DISCOVER packets from the STB.)
DHCP REQUEST packets received: 0
DHCP INFORM packets received: 0
DHCP DECLINE packets received: 0
DHCP packets received from servers: 0
DHCP OFFER packets received: 0
DHCP ACK packets received: 0
DHCP NAK packets received: 0
DHCP packets sent to servers: 0 --- (The DHCP relay device did not forward the DHCP discover packets.)
DHCP packets sent to clients: 0
Unicast packets sent to clients: 0
Broadcast packets sent to clients: 0
Therefore, the problem was caused because the DHCP relay device did not forward DHCP discover packets.
2. Debugged the DHCP relay.
<BSRTRM01>debugging dhcp relay all
Nov 23 2012 15:05:21.810.4+08:00 BSRTRM01 DHCPR/7/dhcpr_debug_paket:
Hardware Type = 1, Hardware Address Length = 6
Hops = 0, Transaction ID = 1846971967
Seconds = 0, Broadcast Flag = 32768
Client IP Address = 0.0.0.0, Your IP Address = 0.0.0.0
Server IP Address = 0.0.0.0, Gateway IP Address = 0.0.0.0
Client Hardware Address = 9094-e428-fd7e
Server Host Name = Not Configured, Boot File Name = Not Configured
Option82 = Not Configured
Dhcp message type = DISCOVER --- Discover packets received
Nov 23 2012 15:05:21.810.5+08:00 BSRTRM01 DHCPR/7/dhcpr debug:
The main IP address of the interface is selected as giaddr(10.31.31.254).
Nov 23 2012 15:05:21.810.6+08:00 BSRTRM01 DHCPR/7/dhcpr_debug_error:
Failed to select IP address of DHCP server.
The DHCP relay device discarded the DHCP discover packets because it failed to find the IP address of the DHCP server.
3. Checked configurations of the relay interface.
vlan-type dot1q 966
description "Connect to METRO E NPEHWTLG22 Gi3/0/0 CCS-RELAY"
ip binding vpn-instance TMCCS
ip address 10.31.31.254 255.255.224.0
ip relay address 10.254.253.65 dhcp-option 82
dhcp select relay
trust upstream default
The server IP address configured on the relay interface was ip relay address 10.254.253.65 dhcp-option 82, which meant that the interface considered that only packets carrying DHCP option 82 could be forwarded to the DHCP server 10.254.253.65.
It was suspected that the problem was caused because the DHCP discover packets did not carry DHCP option82.4. Instructed the frontline personnel to enable DHCP option82 on the downstream MSAN.