DHCP server

[anitachoi3]

Hi,

I config 3 VLANs in the network. There is one DHCP server per VLAN. I would like to achieve following:

VLAN 1: 192.168.11.0

DHCP svr: 192.168.11.23

backup DHCP svr: 192.168.12.23 and 192.168.13.23

VLAN 2: 192.168.12.0

DHCP svr: 192.168.12.23

backup DHCP svr: 192.168.11.23 and 192.168.13.23

VLAN 3: 192.168.13.0

DHCP svr: 192.168.13.23

backup DHCP svr: 192.168.11.23 and 192.168.12.23

Device: Catalyst 3750

Any missing in the config as below?

rdgs

--- config ---

interface GigabitEthernet1/0/1

description VLAN 1

switchport access vlan 1

switchport mode access

!

interface GigabitEthernet1/0/2

description VLAN 2

switchport access vlan 2

switchport mode access

!

interface GigabitEthernet1/0/3

description VLAN 3

switchport access vlan 3

switchport mode access

!

!

interface Vlan1

description User segment 1

ip address 192.168.11.1 255.255.255.0

ip helper-address 192.168.12.23

ip helper-address 192.168.13.23

no ip redirects

no ip unreachables

no ip proxy-arp

!

interface Vlan2

description User segment 2

ip address 192.168.12.1 255.255.255.0

ip helper-address 192.168.11.23

ip helper-address 192.168.13.23

no ip redirects

no ip unreachables

no ip proxy-arp

!

interface Vlan3

description User segment 3

ip address 192.168.13.1 255.255.255.0

ip helper-address 192.168.11.23

ip helper-address 192.168.12.23

no ip redirects

no ip unreachables

no ip proxy-arp

!

----- end ----

[Jon Marshall · Accepted solution]

anitachoi3 wrote:
Hi,
I config 3 VLANs in the network. There is one DHCP server per VLAN. I would like to achieve following:
VLAN 1: 192.168.11.0
DHCP svr: 192.168.11.23
backup DHCP svr: 192.168.12.23 and 192.168.13.23
VLAN 2: 192.168.12.0
DHCP svr: 192.168.12.23
backup DHCP svr: 192.168.11.23 and 192.168.13.23
VLAN 3: 192.168.13.0
DHCP svr: 192.168.13.23
backup DHCP svr: 192.168.11.23 and 192.168.12.23
Device: Catalyst 3750
Any missing in the config as below? 
rdgs
--- config ---
interface GigabitEthernet1/0/1
 description VLAN 1
 switchport access vlan 1
 switchport mode access
!
interface GigabitEthernet1/0/2
 description VLAN 2
 switchport access vlan 2
 switchport mode access
!
interface GigabitEthernet1/0/3
 description VLAN 3
 switchport access vlan 3
 switchport mode access
!
!
interface Vlan1
 description User segment 1
 ip address 192.168.11.1 255.255.255.0
 ip helper-address 192.168.12.23
 ip helper-address 192.168.13.23
 no ip redirects
 no ip unreachables
 no ip proxy-arp
!
interface Vlan2
 description User segment 2
 ip address 192.168.12.1 255.255.255.0
 ip helper-address 192.168.11.23
 ip helper-address 192.168.13.23
 no ip redirects
 no ip unreachables
 no ip proxy-arp
!
interface Vlan3
 description User segment 3
 ip address 192.168.13.1 255.255.255.0
 ip helper-address 192.168.11.23
 ip helper-address 192.168.12.23
 no ip redirects
 no ip unreachables
 no ip proxy-arp
!
----- end ----

Anita

There is nothing missing but be aware that all DHCP servers will be used for each vlan so the local DHCP will see the request but also the 2 ip helper-addresses will see the request per vlan as well. The local one should be the first to respond but that is not always a given.

So you need to make sure that each DHCP server hands out unique addresses per vlan ie. 3 DHCP servers per vlan means each DHCP server is responsible for a 3rd of the subnet for that vlan. You cannot have 2 or more DHCP servers responsible for the same address.

Jon

[Ganesh Hariharan · Accepted solution]

Hi,

Configuring DHCP you need to create pools for alloting ip address for particular vlan,check out the below link for configuraing dhcp in cisco switches.

http://www.cisco.com/en/US/docs/routers/access/1800/1801/software/configuration/guide/dhcpvlan.pdf

and check out the sample configuration regarding dhcp.

ip dhcp pool pool1
   network 10.10.1.0 255.255.255.0
   default-router 10.10.1.1
   dns-server what.ever.ip.itis
!
ip dhcp pool pool2
   network 10.10.2.0 255.255.255.0
   default-router 10.10.2.1
   dns-server what.ever.ip.itis2
vlan 10
ip address 10.10.1.1 255.255.255.0
!
vlan 20
ip address 10.10.2.1 255.255.255.0

the default-router command ties that pool to the interface (vlan)

Hope that helps out your query !!

Regards

Ganesh.H