Load Balancing CNR DHCP Servers behind CSS11506

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May 21st, 2007
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Hi All,

we're trying to enable DHCP on 2 Cisco CNR that are load balanced by a CSS11506. My immediate question is, is this feasible? The two dhcp should be configured with the same address pool right? how can i ensure, that the IP addresses leased by the two CNR will be synchronized with each other? Is it better to just subdivide the pool and assign the first half to the first server and the second half to the second server? Thanks in advance.

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Overall Rating: 1 (1 ratings)
dwaldroop Tue, 05/22/2007 - 12:41
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shouldnt you be running CNR w/replication to do that? regardless of the loadbalancing in front of your CNR cluster.

ronmarcojr Tue, 05/22/2007 - 16:57
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I'm not familiar with the replication part? Could you share some info. Isn't it enough to have the same configuration for the 2 CNR? Thanks.

jreekers Tue, 05/22/2007 - 18:06
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  • Cisco Employee,

Hi Ron.

Please note that CNR 6.2.x has failover load balancing built in which allows both partners to actively lease out addresses (see RFC 3074).

And I'm not sure (I'm not a CSS expert), but I don't think the CSS can load balance port 67 (DHCP).

Here's a snippet about failover load balancing in the Release notes:


You'll find configuration information in the configuaration guide.

Good Luck and hope this helps.


ronmarcojr Tue, 05/22/2007 - 18:24
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Hi Joe,

thanks, i'll look into it, from what i understand, we don't need the CSS to do the load balancing built in to the CNR. The two CNR will simply sync with each other if configured correctly. However, in our current network design, the CNR are already used as DNS servers load balanced by the CSS. we are looking into the possibility of using the same machine to be the DHCP servers. So going back to the problem, how will the CSS affect the configuration of the redundant DHCP in the CNR. Is it even possible? I'll try to verify if the CSS can load balance port 67. Thanks again.

jreekers Tue, 05/22/2007 - 20:36
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If the CSS is unable to load balance the port 67 (DHCP) packet, I don't see that having the CSS in the network will have any effect on the CNR DHCP failover.


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