04-13-2012 02:19 PM - edited 03-07-2019 06:07 AM
Would like to impliment VLAN's on
Cisco IOS Software, C3560 Software (C3560-IPSERVICES-M), Version 12.2(25)SEB4
But I need a DHCP Realy to my Windows Based DHCP Server. How do I enable DHCP Relay on the 3560?
Thanks!
Mark Berry
Solved! Go to Solution.
04-13-2012 02:44 PM
the ip helper command would be on your Layer 3 interface. based on the output you are showing I suspect you are looking at a layer 2 interface. for example a basic config might see something like this:
...
interface GigabitEthernet1/0/1
description L2 interface in vlan 10
switchport access vlan 10
switchport mode access
!
interface GigabitEthernet1/0/1
description L2 interface in vlan 11
switchport access vlan 10
switchport mode access
!
...
interface Vlan10
description Data Vlan
ip address 10.10.10.254 255.255.255.0
interface Vlan11
description Data Vlan two
ip address 10.10.11.254 255.255.255.0
ip helper-address 10.10.10.10
also ensure ip routing is enabled on global config
04-13-2012 02:29 PM
I think it is enabled by default.
Otherwise command:
#:config t
#:service dhcp
04-13-2012 02:32 PM
Oh and surely, i forgot to add
you will have to configure ip helper-address "DHCP server IP" on the interface you want to relay.
04-13-2012 02:37 PM
Thank you for your reply.
But I don’t see a “ip helper-address option.
switch(config-if)#ip ? Shows only
access-group
arp
dhcp
igmp
verify
switch(config-if)#ip dhcp ? reveals only
snooping DHCP Snooping
04-13-2012 02:44 PM
the ip helper command would be on your Layer 3 interface. based on the output you are showing I suspect you are looking at a layer 2 interface. for example a basic config might see something like this:
...
interface GigabitEthernet1/0/1
description L2 interface in vlan 10
switchport access vlan 10
switchport mode access
!
interface GigabitEthernet1/0/1
description L2 interface in vlan 11
switchport access vlan 10
switchport mode access
!
...
interface Vlan10
description Data Vlan
ip address 10.10.10.254 255.255.255.0
interface Vlan11
description Data Vlan two
ip address 10.10.11.254 255.255.255.0
ip helper-address 10.10.10.10
also ensure ip routing is enabled on global config
04-13-2012 03:37 PM
That looks like it! Thanks!
So to recap:
1. Verify DCHP enabled globaly
2. Set ip helper-address on the VLAN (Layer 3) interface that points to the DHCP server.
and that's it eh?
04-13-2012 04:38 PM
If you have your own dhcp server then all you need is the ip helper statement on any L3 interface that is not on the dhcp server subnet.
04-16-2012 07:50 AM
Had never heard the term "Layer Three Interface". Just assumed that all "interfaces" on a L3 switch would be "layer 3 interfaces". So are all "VLAN" interfaces considered "Layer 3 Interfaces" and the physical "ports/interfaces" are considered "layer 2 interfaces"?
04-16-2012 08:59 AM
The answer is the ports can be either . You can make the ports a "routed" L3 port where you put the ip address directly on the port itself with the "no switchport" command or you can make the ports a layer 2 port with the "switchport" command and then if you want to route traffic on that port you would create a "SVI" aka "interface vlan X and assign those ports into the vlan . It really depends on what you are trying to accomplish with the port or design considerations on how you set it up .
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