01-08-2007 12:25 AM - edited 03-05-2019 01:38 PM
Dear All;
i need help; I have three switches, 2960(2) 3750 (1) having 6 VLANs. My PC is attached with 2960 switch on VLAN 2. this switch is attached with 3750 switch via trunk. i have DHCP server attached on VLAN 6 on 3750 switch. but my PC is not able to contact with DHCP server. My configurations are:
On Switch 2960;
VLANs = 2 & 3
service dhcp
ip dhcp relay information policy replace
VTP domain = ABC
VTP mode = Cient
TRUNK = trunk on
ON Switch 3760;
VLANs = 4,5&6
service dhcp
VTP domain = ABC
VTP mode = server
TRUNK = switchport mode trunk
when i attached my PC in default VLAN on other side DHCP server on default VLAN (Both are in same VLANs) then it works fine and get IP address from DHCP server. but when i Attached my PC on VLAN2 in first switch (2960) and DHCP server on another VLAN 6 (on 3750 Switch) then it doen't work. i need help.
01-08-2007 12:31 AM
Hi Friend,
Can you please confirm if 3750 doing intervlan routing between your all vlans? If not that which router/switch is doing an inter vlan routing between your vlan 2 and vlan 6. I do not see vlan 2 configured on your 3750 switch? Can you please confirm.
Also the router/switch who is doing routing between your vlan 2 and vlan 6 on that router/switch you need to add "ip helper-address
Please revert back if you have any doubts.
HTH
Ankur
*Please rate all helpfull post
01-08-2007 12:53 AM
Hi dear friend;
Thank you very much for your kind reply;
you are right. 3750 switch is my core switch but i didn't configure it for interVLAN routing. nodoubt TRUNK port which i configured,is part of all VLANs. this port should route source VLAN traffic to destination VLAN traffic. if not then it means i have to configure 3750 for Inter VLAN routing.
on the other hand it means i have to configure the IP helper-address command in all VLAN interfaces on both switches? so could you please giude me further.
i will wait for your kind reply
01-08-2007 01:00 AM
Hi Friend,
Yes you have to configure inter vlan routing on your 3750 switch so that vlan 2 can talk to vlan 6 and all vlans can talk to each other. Trunk allow to pass all vlans but will not route packets.
Trunk will make your vlan 2 pc on 2960 talk to vlan 2 pc on 3750 but not any pc in vlan 6.
So just configure 3750 for intervlan routing like this
Switch(config)#ip routing
!
Switch(config)#interface vlan 2
Switch(config-if)#ip address
Switch(config-if)#ip helper-address
Switch(config-if)#no shut
!
Switch(config)#interface vlan 4
Switch(config-if)#
Switch(config-if)#ip helper-address
Switch(config-if)#no shut
!
Switch(config)#interface vlan 6
Switch(config-if)#ip address
Switch(config-if)#no shut
You need not configure "ip helper-command".
Once you are done with the same, everything should work fine.
Also you can have a look at this link which will guide with inter vlan routing config
http://www.cisco.com/en/US/tech/tk389/tk815/technologies_configuration_example09186a008015f17a.shtml
HTH
Ankur
*Pls rate all helpfull post
01-08-2007 12:33 AM
Is your 3750 switch acting as the layer 3 switch ie. do you have the routed interfaces for the vlans on this switch.
if so you need to add the following under the vlan 2 layer 3 configuration on the 3750 switch
ip helper-address "address of DHCP server"
HTH
01-08-2007 12:55 AM
you are right. 3750 switch is my core switch but i didn't configure it for interVLAN routing. nodoubt TRUNK port which i configured,is part of all VLANs. this port should route source VLAN traffic to destination VLAN traffic. if not then it means i have to configure 3750 for Inter VLAN routing.
on the other hand it means i have to configure the IP helper-address command in all VLAN interfaces on both switches? so could you please giude me further.
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