07-14-2010 05:45 AM - edited 03-06-2019 12:01 PM
Hi expert,
Refer to my attached diagram, Can I setup that when LAN user want to get IP address from DHCP server, first choice will query 192.168.1.1 dhcp server. Once 192.168.1.1 dhcp server is down, then will query 172.16.1.1 dhcp server.
thank you
07-14-2010 06:27 AM
Dear,
Yes you can.
For this you need to add following cmd on LAN segment vlan int.
int vlan XX
ip address ...................
ip helper-address 192.168.1.1
ip helper-address 172.16.1.1
If you have any doubt, pls post config.
than I can tell you where exactly need to add these cmds.
Hope this will help you
Rate the post if it will help you.
Regards
07-14-2010 06:37 AM
Dear sir,
You mean below configuration can make me to request dhcp request from 192.168.1.1 first, once 192.168.1.1 server is down, it will drop to the second one
172.16.1.1 ?
My configuration is
int vlan 100
ip address 100.100.100.1 255.255.255.0
ip helper-address 192.168.1.1
ip helper-address 172.16.1.1
Then if I change to
int vlan100
ip address 100.100.100.1 255.255.255.0
ip helper-address 172.16.1.1
ip helper-address 192.168.1.1
that means first query dhcp server 172.16.1.1 first, once 172.16.1.1 is down, it will query to 192.168.1.1 ?
Any document has publish it ?
Thanks!
07-14-2010 07:34 AM
Unfortunately Dipesh is incorrect when he says that you can specify a DHCP server to querry first. If you configure 2 ip helper address commands then IOS will forward requests to both of them. It is likely that both will respond and in that case the client usually accepts the first one that responds. There is not a way in IOS to achieve what you want, that the request will go to a primary and only if that one is down will go to a secondary.
HTH
Rick
07-14-2010 07:43 AM
Dear sir,
You mean there is no way to control what is first and what is second, Client receive IP address is base on which dhcp respond is faster. Am I right ?
07-14-2010 09:20 AM
Yes you are right. With ip helper-address there is not a way to establish priority.
HTH
Rick
07-14-2010 09:36 PM
Dear,
I am not saying the priority of helper address.
But the reachability to DHCP server.
Suppose One DHCP server is in other segment and one DHCP server in the sane local segment than the dhcp server in the local segment will reponse first.
for 172.X.X.1 is other side of router so it will be reached second. 1st will use the dhcp server on local segment and if it will down than go for second one.
Regards,
07-14-2010 11:10 PM
Reachability could be checked by SLA. May be it is possible to do anything this way?
05-26-2022 08:11 AM
Did you imagine to play with the routing metrics?
05-26-2022 12:06 PM
Clearly what the original poster wanted to achieve is to have 2 servers configured in a way that the router would send requests to only one server. If 192.168.1.1 is available the request is sent to this and if that server is no longer available then the request is sent to 172.16.1.1. How would you suggest that routing metrics could achieve this?
This question is very old and technology has changed. If I were answering that question today I might suggest that you might be able to combine tracking availability of 192.168.1.1 and an EEM script that could detect loss of connectivity to 192.168.1.1 and would then change the configuration to use 172.16.1.1. (and probably another EEM script to detect when 192.168.1.1 becomes available and revert to the original server)
Discover and save your favorite ideas. Come back to expert answers, step-by-step guides, recent topics, and more.
New here? Get started with these tips. How to use Community New member guide