Is it possible to have multiple DHCP Servers in a Single VLAN ?

Unanswered Question
Dec 12th, 2009

Hi,

I have one 4500 Core switch  and currently  have one DHCP Server .

But now the client requires one more DHCP Server in their network for redundancy or Failover in the same VLAN.

Is it possible to have multiple DHCP servers in a single VLAN ??

Pls advice..

Thanks ,

Mahesh

I have this problem too.
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ohassairi Sun, 12/13/2009 - 00:19

yes it is possible.

the first that will answer will offer the IP address.

but in order to avoid ip conflict devide your IP scope in 2 parts :

for example if you have the range 192.168.1.1 ---> 192.168.1.254 then give server 1 the scope: 192.168.1.1 ---> 192.168.1.128 and server 2 :

192.168.1.129 ---> 192.168.1.254

or try to see if you can form a DHCP server cluster.

think also about implementing DHCP snooping to avoid DHCP attacks

Magesh G. Sun, 12/13/2009 - 01:03

hi ,

thanks for the reply...

If we have multiple vlans in the network.. is there any changes to be done to VLAN interface config in my L3 switch ?

currently i have one ip helper address < dhcp server 1>  configured on the vlan interface .

Please revert.

Thanks ,

Jon Marshall Sun, 12/13/2009 - 02:10

magesh2005 wrote:

hi ,

thanks for the reply...

If we have multiple vlans in the network.. is there any changes to be done to VLAN interface config in my L3 switch ?

currently i have one ip helper address < dhcp server 1>  configured on the vlan interface .

Please revert.

Thanks ,

Yes, you will need to add a second "ip helper-address x.x.x.x" command under your L3 vlan interfaces for the 2nd DHCP server.

Jon

vvasisth Sun, 12/13/2009 - 02:49

yes you can have multiple dhcp servers for a vlan.

and the ip helper command is used to just convert the broadcast packet and send it as a unicat packet to the ip add defined in the command this command is mostly used when you have the dhcp server in a diff vlan.

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