DHCP server

Answered Question
Dec 26th, 2009

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 ----

Correct Answer by Ganesh Hariharan about 7 years 2 months ago

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

Correct Answer by Jon Marshall about 7 years 2 months ago

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

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Correct Answer
Jon Marshall Sat, 12/26/2009 - 06:59

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

Correct Answer
Ganesh Hariharan Sat, 12/26/2009 - 07:01

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

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