DNS & DHCP across a WAN - Max latency?

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Jul 3rd, 2008
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We're doing a global WAN migration to a centralised model where the DHCP & DNS are being hosted on devices in a datacentre.

Most of the 1000 sites will connect over MPLS with nice low latencies. Some however will be IPSEC over the internet from Africa.

What are the maximum possible latencies before DHCP will timeout, and DNS will fail to resolve?

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paolo bevilacqua Thu, 07/03/2008 - 02:12
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Hi, these are robust services. Even 5 secs is not a problem.

Note, DHCP, is much, much, much better if handled by the local router or server. Real problem is not delay, but circuit unavailability.

Please rate post if it does!

raycourtney Fri, 07/04/2008 - 00:44
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Thanks for the answer. If the timeout is 5 seconds then we should be ok, even with a DSL line in the middle of Africa :)

DHCP works well on a local router but is not a scalable manageable solution. We have 1100 sites and a single IP address scheme so we can manage it much better from a central device.


paolo bevilacqua Fri, 07/04/2008 - 01:02
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I understand the manageability concerns, but expect a lot of issues with a central DHCP.

Once the initial configuration is correctly made in the local router, it becomes a rugged service with no external dependencies and viretually no maintenance required. It is not the same (actually the opposite) for relayed DHCP.

Who tried before you, finally found that service on the router is the most reliable and the less maintenance-requiring solution.

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raycourtney Fri, 07/04/2008 - 01:26
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This is not my decision to make, unfortunately, but i do have to justify it to a lot of regional techs and managers as a viable design decision.

You have sown the seeds of doubt now.... :)

paolo bevilacqua Fri, 07/04/2008 - 02:46
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I'm specialized in sowing doubt. To be honest with you, I've been found right more often than not.

Good luck!


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