The problem you are having is due do DHCP functionality, not
cisco/helper address related.
The DHCP server which does not have a scope created on it is issuing a
NACK for the IP request to the client. This is probably happening first
because the NACKing server can tell that it is not configured with a
scope for the requesting net faster than the assigning server can do a
lookup and find a valid IP to assign. The client gets the NACK first
and gives up.
You can solve this one of two ways:
Remove the helper address pointing to the second server. If its not
configured to serve that subnet, then you are not gaining anything by
having the helper address there, and actually causing you a problem.
Alternately, if you want redundancy, split the scope between the two
servers (as someone else has already suggested). Each DHCP server must
have scopes defined on it for the nets it is receiving requests from or
else it will generate the NACK.
I have this problem all the time when an enterprising user installs NT
Server with "all the options" (including DHCP Server) on their
workstation. The enterprising user doesn't know anything about DHCP,
leaves the scope empty (default), and DHCP on his broadcast domain
grinds to a hault as his box starts NACKing valid requests.
-S.
Gayathri wrote:
>
> Firstly, sorry for the repeated submission, I dont see my psoting under the
> main heading so I am forced to post it again..
>
> here is my question...
>
> I have 2 DHCP servers and I have defined both the IP helper addressess in
> our routers
>
> Now, if a client quieries for an IP, which of the servers will respond
> first?
>
> The problem I have is we have defined one subnet in DHCP Server and not in
> the other.
>
> When this user is querying for an IP , he is not getting a response.
>
> interface Ethernet0
> ip address 10.X.X.X 255.255.0.0
> ip helper-address 10.X.1.X
> ip helper-address 10.X.1.Y
>
> The said subnet is defined in the DHCP server 10.102.1.Y but, still there
> is no response. when the client requests.
>
> The main reason we have 2 DHCP servers is for redundancy.
>
> Please note that they are independant of each other .
>
> Does this mean that , when the client is requesting, the router first
> forwards to the first DHCP server and since it is not getting a response ,
> is dropping it?
>
> Thanks
>
> Gayathri
>
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