Re: Multiple DHCP servers

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jtdrummerboy,

When a DHCP client decides to look for a new address or refresh the one it
has (at 50% of the lease duration) it does a broadcast on the network looking
for available servers. In all cases, it will accept the first one that
replies back -- this is why ACE knew it was the faster server. Since
broadcasts don't cross routed boundaries by default only servers on the
subnet are in the running. You can use IP Helper (IP Helper-address in cisco)
to allow for DHCP requests to cross the boundary.

An 80/20 scenario is implemented to provide higher availability for DHCP in
the case that one server goes down. It should never be used to extend the
scope. You should use larger scopes or superscopes to grow capacity. When
the primary server goes down, you have the time that it takes the 20% to get
used to fix the problem before you start impacting the users.

It should also be noted that you shoudl authorize both servers to host the
ENTIRE range and use exclusions to mask the 80/20 scenario. Otherwise you
get NAK poisoning when a client goes to refresh and hits the "other" server
for some reason. You want it to respond with a differnt valid response
rather than issue a NAK telling the client that the range isn't valid. In
some cases, the client doesn't try again and the IP stack goes down.

Hope this helps.
--
Ryan Hanisco
MCSE, MCTS: SQL 2005, Project+
Chicago, IL

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"jtdrummerboy" wrote:

Hi Scott, thanks for your quick response. Both of these servers reside on
the same subnet so I agree with your theory that it would be difficult to
give priority to one over the other. I do also agree with Ace's response to
give the larger pool to the one that acknowledges more requests...I was just
trying to avoid this as this server is more heavily used.

"Scott Lowe" wrote:

In article
<C665BE2C-DD13-46FD-9990-C1AE279797EB@xxxxxxxxxxxxx>anRkcnVtbWVyYm95
<jtdrummerboy@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

Ace, If I wanted to set priority to one over the other, is there a
way of doing that? The faster of the 2 servers is indeed the one
that keeps running out of addresses, however, I want the other server
to be the primary to distribute addresses. Does this make sense?


It does indeed make sense, but AFAIK there is no way to do this (not
if both servers are on the same subnet as the clients). In a routed
environment where you are using DHCP relays, this is probably
possible; however, we don't know if this would apply to your network.

Regards,
Scott


--

I'm trying a new usenet client for Mac, Nemo OS X.
You can download it at http://www.malcom-mac.com/nemo


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