DHCP for different vlans - Cisco Community

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Hi All,

I need to set up 10 or so switches in my network with 8 different vlans. I've connected them via Fiber as the runs are longer than the ethernet standard.

The issue i'm having is getting DHCP to work from our corporate vlan which is on a different (vlan) subnet than the other 9 switches. I want DHCP to be handed out from a windows DHCP server and i've set up all the vlan's with the IP helper address of the DHCP server IP that is on our corp vlan.

The switches are connected via trunk and i've also ensured that all the vlans are allowed through the trunk. Is there something i'm missing?

If I add the port (switchport access vlan 2) to one of the vlans that the DHCP server is connected to, the DHCP will work but thats only for one vlan. How can i get DHCP working for all the vlans?

Thanks,

11 Replies 11

Hello,

You are saying that you have already implemented IP helper address. Did you encounter any proplem?

For each VLAN you have a corresponding interface VLAN in your L3 switch so you only need to set this command only on your L3 interfaces.

"IP helper-address [ DHCP server ip address]. For interface VLAN 2, you do not need to set this command.

As an example,

int vlan 2

des DHCP server

ip address 192.168.2.1 255.255.255.0

int vlan 3

des Client group 1

ip address 192.168.3.1 255.255.255.0

ip helper-address 192.168.2.2 [DHCP server IP]

int vlan 4

des Client group 2

ip address 192.168.4.1 255.255.255.0

ip helper-address 192.168.2.2 [DHCP server IP]

and so on

Please let me know if I understood your question correctly

Masoud

I've already set the Ip helper-address but the nodes on the network are not receiving DHCP from the DHCP server on the corp network that is on the 192.168.0.0 network (vlan 10)

interface Vlan2

ip address 192.168.50.1 255.255.255.0

ip helper-address 192.168.0.10

!

interface Vlan3

ip address 192.168.51.1 255.255.255.0

ip helper-address 192.168.0.10

!

interface Vlan4

ip address 192.168.52.1 255.255.255.0

ip helper-address 192.168.0.10

!

interface Vlan5

ip address 192.168.54.1 255.255.255.0

ip helper-address 192.168.0.10

!

interface Vlan7

ip address 192.168.55.1 255.255.255.0

ip helper-address 192.168.0.10

!

interface Vlan10

ip address 192.168.0.1 255.255.255.0

ip helper-address 192.168.0.10

!

interface Vlan16

ip address 192.168.56.1 255.255.255.0

ip helper-address 192.168.0.10

Can you ping DHCP server with the source of for example 192.168.51.1 ?

some thing like this

ping 192.168.0.10 source 192.168.51.1 [on your L3 switch]

Set debug IP DHCP on you L3 switch while terminal moniter is on and try with one client. Please share the output.

Masoud

Thanks, I was able to figure out the channel-group wasn't configured properly causing the the port channel not to be up, up. Now its good. Thanks for the help!

It means your whole network was down.You had some computers connected to fa0/1 and fa0/2.

interface FastEthernet0/1 switchport access vlan 2

interface FastEthernet0/2 switchport access vlan 2

At least, they should have worked even your portchannel was down,

Masoud

I am glad your problem was solved.

Masoud

Adding to my previous command.

Which Vlan is associated with DHCP server?

You need to have something like this

int vlan X [ X in the same VLAN of your DHCP server]

des DHCP server

ip address 192.168.0.1 255.255.255.0 [ in the same range of you DHCP server]

here is the output of the debug

Sending 5, 100-byte ICMP Echos to 192.168.0.10, timeout is 2 seconds:

Packet sent with a source address of 192.168.51.1

IP: tableid=0, s=192.168.51.1 (local), d=192.168.0.10 (Vlan10), routed via RIB

IP: s=192.168.51.1 (local), d=192.168.0.10 (Vlan10), len 128, sending

IP: tableid=0, s=192.168.0.10 (Vlan10), d=192.168.51.1 (Vlan3), routed via RIB

IP: s=192.168.0.10 (Vlan10), d=192.168.51.1 (Vlan3), len 128, rcvd 3

.

IP: tableid=0, s=192.168.51.1 (local), d=192.168.0.10 (Vlan10), routed via RIB

IP: s=192.168.51.1 (local), d=192.168.0.10 (Vlan10), len 128, sending

IP: tableid=0, s=192.168.0.10 (Vlan10), d=192.168.51.1 (Vlan3), routed via RIB

IP: s=192.168.0.10 (Vlan10), d=192.168.51.1 (Vlan3), len 128, rcvd 3

.

IP: tableid=0, s=192.168.51.1 (local), d=192.168.0.10 (Vlan10), routed via RIB

IP: s=192.168.51.1 (local), d=192.168.0.10 (Vlan10), len 128, sending

IP: tableid=0, s=192.168.0.10 (Vlan10), d=192.168.51.1 (Vlan3), routed via RIB

IP: s=192.168.0.10 (Vlan10), d=192.168.51.1 (Vlan3), len 128, rcvd 3

.

IP: tableid=0, s=192.168.51.1 (local), d=192.168.0.10 (Vlan10), routed via RIB

IP: s=192.168.51.1 (local), d=192.168.0.10 (Vlan10), len 128, sending

IP: tableid=0, s=192.168.0.10 (Vlan10), d=192.168.51.1 (Vlan3), routed via RIB

IP: s=192.168.0.10 (Vlan10), d=192.168.51.1 (Vlan3), len 128, rcvd 3

.

IP: tableid=0, s=192.168.51.1 (local), d=192.168.0.10 (Vlan10), routed via RIB

IP: s=192.168.51.1 (local), d=192.168.0.10 (Vlan10), len 128, sending

IP: tableid=0, s=192.168.0.10 (Vlan10), d=192.168.51.1 (Vlan3), routed via RIB

IP: s=192.168.0.10 (Vlan10), d=192.168.51.1 (Vlan3), len 128, rcvd 3

.

Success rate is 0 percent (0/5)

VLAN 10 is where the DHCP server is

Success rate is 0 percent (0/5)

It means that switch does not see your DHCP server.

Try these and give me feedback

1-

If DHCP server is connected to fa0/1 then you need to config the port this way

interface fa0/1

switchport access vlan 10

Try to test direct connectivity

Ping 192.168.0.10 from DHCP sever (give me the result)

2- DHCP server must have gateway. Gateway must be 192.168.0.10

3-turn windows firewall off

and then try the previous ping

ping 192.168.0.10 source 192.168.51.1

Masoud

The DHCP server is connected to port g0/2. The core switch IP is 192.168.0.1. I can ping the DHCP server (192.168.0.10) from the switch as it is directly connected and I gave the DHCP server a gateway of the core L3 switch.

Attached running config of core switch.

3 KB

Config looks good in terms of vlaning and DHCP relay.

interface Vlan10
description CORP
ip address 192.168.0.1 255.255.255.0
ip helper-address 192.168.0.10

You do not need to set the above bold command.

Did you set gateway after my comment? or it was set before?

Can you ping ?

ping 192.168.0.10 source 192.168.51.1

or

ping 192.168.0.10 source 192.168.50.1

And also do not forget windows firewall

Masoud

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