dhcp server on another vlan

[robertkwild]

Hi all,

I have 2 vlans one host is on vlan 1 and vlan 2 has the dhcp server

For this to work do I only have to add the ip helper address on vlan 1 interface to point to the dhcp server ip on vlan 2

Ie

Int vlan 1

Ip helper-address (ip of dhcp server)

Thanks,

Rob

[Georg Pauwen]

Hello,

the short answer is: yes. You are correct.

[robertkwild]

So I don't need to add ip addresses for both vlans so they can talk to each other ie for example

Int vlan 1

Ip address ip subnet

Int vlan 2

Ip address ip subnet

These vlans do talk to each other eventually on another layer 3 switch that have got ip addresses for all vlaning ie inter vlanning

[Georg Pauwen]

Hello,

you also need IP addresses on both vlan interfaces in order for clients in both vlans to be able to talk to each other.

[robertkwild]

So I need ip addresses for both vlans on this switch, even tho its not the router/gateway switch ie the main switch where all the intervlanning happens?

Also what about dhcp relay address, is this what I need aswell

[balaji.bandi]

yes you need both VLAN to mention ip-helper-address, routing take place where Layer 3 SVI is configured.

[Georg Pauwen]

Hello,

no. If the switch is not doing the inter-vlan routing, you do not need to configure anything (no IP address or ip helper-address). The IP address on a layer 2 switch is only used for management.

So, if your topology looks like this:

PC --> Layer 2 Switch --> Router (with DHCP server with e.g. IP address 192.168.2.5 connected to Vlan 2), the IP addresses and helper addresses need to be on the router. The router config would look like this (if you are using subinterfaces in a Router-on-a-stick setup):

interface GigabitEthernet0/0/0

description Downlink to Switch

ip address 192.168.1.1 255.255.255.0

ip helper-address 192.168.2.5

!

interface GigabitEthernet0/0/0.2

encapsulation dot1q 2

ip address 192.168.2.1 255.255.255.0

If you are using a layer 3 switch, the config would look like this:

interface Vlan 1

ip address 192.168.1.1 255.255.255.0

ip helper-address 192.168.2.5

!

interface Vlan 2

ip address 192.168.2.1 255.255.255.0

In both cases, obviously make sue that the port connecting the layer 2 switch to the layer3 switch/router is configured as a trunk.

[paul driver]

Hello

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@robertkwild wrote:

Hi all,

I have 2 vlans one host is on vlan 1 and vlan 2 has the dhcp server

For this to work do I only have to add the ip helper address on vlan 1 interface to point to the dhcp server ip on vlan 2

---

No you dont need any ip helper address, you just need the switch to perform L3 routing between the two vlans