NEC IP8800/S2400 Series Troubleshooting Manual page 121

Figure 3-10: Troubleshooting for DHCP Server Failure with DNS Cooperation
Verify if there is a failure occurrence using the show logging
command and the show ip interface command.
No failure on this
system
(Connected directly)
Verify the failure occurrence on other devices.
Verify the setting information of filter
and QoS.
(a) Checking configuration
This failure may be caused by the incorrect DNS update on Dynamic DNS due to the DHCP server errors or the conflict
with the settings on the DNS server. The followings are the steps to check the configuration:
1. First, check the method for permitting DNS update on the DNS server. For access permission with an IP address/
network, see No. 3 and later. For permission with an authentication key, see No. 2 and later.
2. Confirm that the key information and authentication key specified on the DNS server are equivalent to the key
information set in the DHCP server configuration (see the manual "Configuration Commands").
3. Confirm that the zone information specified on the DNS server is equivalent to the zone information in the DHCP
server configuration (see the manual "Configuration Commands"). In this case, confirm that both forward lookup
and reverse lookup are set.
4. Confirm that DNS update is defined (see the manual "Configuration Commands"). Since the DNS update is disabled
by default, this setting is required to update DNS.
5. Confirm that the domain name used by the client matches the domain name registered on the DNS server. When
distributing the domain name by DHCP, confirm that it is correctly set in the configuration (see "Configuration
Commands" and "Operation Commands").
(b) Checking time information
When the authentication key is being used for DNS update, the difference in time between this system and the DNS
server should be within 5 minutes as the UTC time in most cases. Use the show clock command to check the time
information on this system and synchronize the time information referring to "Configuration Commands" and
"Operation Commands," as required.
(c) Checking the log message and interface
As one of the causes for disabled communication to the DNS server, communication between the DNS server and
DHCP server has been disabled. Check the log message displayed on this system or the interface up/down status using
the show ip interface command. For the procedure, see
<DNS update disabled>
Check the configuration.
No failure on this system
(Multiple devices exist
between DNS server and
DHCP server.)
No failure on other devices
See the manuals "Message Log Reference"
and "3.6.1 Communication Is Disabled or Is
Disconnected" and perform the actions
described in [Action] associated with each log
"3.6.1 Communication Is Disabled or Is
3.
Troubleshooting Functional Failures in Operation
A failure occurred on
this system
message.
Disconnected."
59