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address of interface vlan1 as 192.168.40.50, configure the address of DHCP Relay forwarding
as 192.168.40.199, configure vlan3 as a sub-vlan of vlan1. The configuration is as follows:
switch(config)#vlan 1
switch(config)#vlan 3
switch(config)#interface ethernet 1/2
Switch(Config-If-Ethernet1/2)#switchport access vlan 3
switch(config)#interface ethernet 1/3
Switch(Config-If-Ethernet1/2)#switchport mode trunk
switch(config)#service dhcp
switch(config)#ip forward-protocol udp bootps
switch(config)#ip dhcp relay information option
switch(config)#ip dhcp relay share-vlan 1 sub-vlan 3
switch(config-if-vlan1)#ip address 192.168.40.50 255.255.255.0
switch(config-if-vlan1)#ip helper-address 192.168.40.199
31.5 DHCP Troubleshooting
If the DHCP clients cannot obtain IP addresses and other network parameters, the following
procedures can be followed when DHCP client hardware and cables have been verified ok.
Verify the DHCP server is running, start the related DHCP server if not running.
In such case, DHCP server should be examined for an address pool that is in the
same segment of the switch VLAN, such a pool should be added if not present, and
(This does not indicate switch cannot assign IP address for different segments, see
solution 2 for details.)
In DHCP service, pools for dynamic IP allocation and manual binding are conflicting,
i.e., if command "network-address" and "host" are run for a pool, only one of them
will take effect; furthermore, in manual binding, only one IP-MAC binding can be
configured in one pool. If multiple bindings are required, multiple manual pools can
be created and IP-MAC bindings set for each pool. New configuration in the same
pool overwrites the previous configuration.
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Troubleshooting
