Add another ip helper-address into interface vlan

[getaway51]

Hi,

Currently each vlan int have ip helper-address configured which points to a MS DHCP server.

If I add in another cmd of ip helper-address <server2>, which server the vlan int will relay out dhcp req?

will this even affect the first DHCP cmd- "ip helper-address <MS DHCP IP>"?

conf t

int vlan 390

ip helper-address 10.5.5.1

Will it goes automatically to the secondary line of ip helper-address? 1st line is the existing ip helper-address cmd.

[marce1000]

 https://community.cisco.com/t5/switching/multiple-ip-helper-address-is-possible/td-p/1782182

 M.

[balaji.bandi]

You can do like below if you like order will be 1 and 2 so on ...

Make sure you can also split the DHCP scopes to different DHCP Servers.

conf t

int vlan 390

ip helper-address 10.5.5.1

ip helper-address 10.5.5.2

[getaway51]

Is there any difference if i move the order of the line?
Anything affected?

[julian.bendix]

Hi!

No the order shouldn't matter.

The DHCP Packets will be changed to unicast and forwarded to all IP-Helpers!

Best regards
Julian

[hm660522267]

In this case you can add a second ip helper and there will be no preference in the order, just forward to helper IPs. Be sure to not have the same scope across both servers or you may experience your clients will get DORA from both DHCP but use one which reaches relay the fastest. Not recommended as overlapping bindings on both servers.

If you want common method for DHCP redundancy is to take your typical /24 subnet and divide it into two /25s for your scopes (one per server). This way the VLAN is allocated to the /24 subnet only but sends out to helper addr and no overlap with binding on only one DHCP server. Note that in this one server will do full DORA and other will discover then request (from my test).

Set bigger scopes or higher lease time so both redundant pools dont get exhausted, or you can configure servers under a virtual IP with load balancing for server redundancy.

Hussain