Troubleshooting guide

3. Troubleshooting Functional Failures During Operation
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No. Items to check and commands Action
4 Check the filtering configuration. Certain packets might have been discarded by filtering or packets
might have been discarded by the shaper of QoS control. Make sure
that the setting conditions for filtering and QoS control in the
configuration are correct, and that the shaper is used appropriately in
the system configuration. For details about the procedure, see 3.13.1
Checking the filtering and QoS control configuration information.
5 Setting the authentication IPv4
access list
[Fixed VLAN mode] [Dynamic VLAN mode]
Make sure that the filtering conditions required for communication
from unauthenticated terminals to destinations outside the Switch
have been set correctly by using the authentication ip
access-group and ip access-list extended configuration
commands.
6 Setting of ARP packet forwarding [Fixed VLAN mode] [Dynamic VLAN mode]
Make sure that the authentication arp-relay configuration
command is set correctly so that unauthenticated terminals can send
ARP packets to devices outside the Switch.
(1) Communication failures occurring when the DHCP server is used
There are three probable causes for problems such as disabled address distribution to
clients that might occur during communication with the DHCP server:
1. A configuration is set incorrectly.
2. The network configuration is changed.
3. The DHCP server fails.
First, check for cause 1. Described below are likely examples of incorrect configuration.
For cause 2, check the differences in the network configuration before and after the change
to uncover any cause that could disable communication. You might have checked the client
and server settings (such as network card settings and cable connections) and concluded
that cause 3 applies. For example, the configuration and network configuration are correct,
but IP communication is not possible due to disabled allocation of IP addresses to clients.
In such a case, see
(b) Checking the operation log and interface through to (d) Checking
the filtering and QoS configuration information for details.
(a) Checking the configuration
It can be assumed that IP addresses cannot be allocated to clients if the resources on the
DHCP server are configured incorrectly. To check the configuration, do the following:
 In the configuration, make sure there is an
ip dhcp pool setting that contains the
network setting for the IP addresses to be assigned to the DHCP clients.
 In the configuration, make sure the number of IP address pools to be assigned to a
DHCP client is larger than the number of concurrently used clients set in the
ip dhcp
excluded-address configuration command.
 When an external DHCP server is used, check the setting on the device to be used
as a DHCP relay agent.
(b) Checking the operation log and interface
One probable cause of disabled assignment of IP addresses to clients is that
communication between the client and the server has been disabled. Check the operation
log displayed by the Switch or use the
show ip interface operation command to check
whether the interface status is
Up or Down. For details about the procedure, see 3.4 Network
interface communication failures.