Troubleshooting guide

3. Troubleshooting Functional Failures During Operation
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3. If the routing information obtained by the Switch does not contain the routing information
about the interface that caused the communication failure or contains an incorrect address of
the interface's next hop, see 3.8 IPv4 unicast routing communication failures.
4. If the routing information obtained by the Switch contains routing information about the
interface that caused the communication failure, the interface might have a problem with the
functionality shown below. That functionality must be checked.
• Filters and QoS functionality
See (f)Checking the filters and QoS configuration information.
• DHCP and BOOTP functionality
See (g)Checking the DHCP and BOOTP configuration information.
(f) Checking the filters and QoS configuration information
Filtering might have been set to discard only specific packets or packets might have been discarded
by bandwidth monitoring, drop control, or the QoS control shaper.
Make sure that the setting conditions for filters and QoS control in the configuration are correct,
and that bandwidth monitoring, drop control, or the shaper is used appropriately in the system
configuration. For details about the procedure, see 3.25.1 Checking the filters and QoS
configuration information.
In addition, if DHCP snooping is used, packets might have been discarded by a terminal filter.
Check whether the setting conditions for DHCP snooping in the configuration are correct. For
details about the procedure, see 3.27 DHCP snooping problems.
(g) Checking the DHCP and BOOTP configuration information
If many of the IP addresses to be leased are left on the DHCP or BOOTP server, it can be assumed
that IP addresses cannot be assigned to clients due to incorrect configuration settings for the DHCP
or BOOTP relay. The following describes the operations for checking the configuration.
1. Check whether the IP address of the DHCP or BOOTP server or the IP address of the next
router with the DHCP or BOOTP relay agent functionality is set for
ip helper-address.
2. Check whether
ip helper-address is set for the client interface.
3. Check whether the value of
ip bootp-hops is set to a bootp hops value that is correct from
the viewpoint of the client.
4. For a multihomed configuration, check whether the value of
ip relay-agent-address is the
same as the subnet of the IP address distributed by the DHCP or BOOTP server.
5. If DHCP snooping is used, packets might have been discarded by DHCP snooping. Check
whether the setting conditions for DHCP snooping in the configuration are correct. For details
about the procedure, see 3.27 DHCP snooping problems.
(h) Checking when the DHCP relay and VRRP are operated on the same interface
If the DHCP or BOOTP relay and VRRP are operated on the same interface, the DHCP or BOOTP
client gateway address (router option) on the DHCP or BOOTP server must be set to the virtual
router address that is set in the VRRP configuration. If the gateway address is not set as above, after
switching between the master and standby routers is performed by VRRP, the communication of
the DHCP or BOOTP clients might be disabled. To check the settings, follow the procedure for
checking the settings for each DHCP or BOOTP server.
(2) Communication problems on the DHCP server
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.