Load Balancing DHCP Servers

[Douglas Power]

Have a look here:
http://www.madboa.com/geek/dhcp-failover/



On Thu, 2007-05-03 at 15:45 +0100, Simon Hobson wrote:
> Aggarwal Vivek-Q4997C wrote:
> 
> >There are 4 DHCP Servers and on router working as a relay agent for 4
> >DHCP servers
> >
> >
> >
> >Now I want these 4 DHCP Servers to work in Load Balance Scenario means
> >if first request comes it goes to 1st server, 2nd request to 2nd Server,
> >3rd request to third and so on and if anyone server fails request is
> >automatically forwarded to another server.
> >
> >
> >
> >Im using ISC DHCP 3.0 version and LINUX Operating system
> >
> >
> >
> >Is it possible? If yes how can I achieve it? What should be
> >configuration of the servers and the relay agent?
> 
> No, that is not how DHCP works, and it makes no difference what 
> server and relay agent you use.
> 
> Firstly, DHCP is a stateful function - the server that handles a 
> query must know about the state of both the client making the query 
> and other clients on the network. Consider if the relay agent sends a 
> clients request to one server, then on the next boot/wake from 
> sleep/whatever, sends the request to a different server. Unless the 
> servers are synchronised then the second server knows nothing about 
> the client and chaos ensues on your network.
> 
> With the ISC server you can run two (and only two) servers in a 
> failover configuration. They will keep each other informed of what 
> offers they have made so that both have the same view of the network 
> at all times.
> 
> With care you can run more than one server without failover. 
> Typically you either :
> - Find a 'key' that can differentiate classes of clients so that one 
> server only serves one set of clients while the other server ignores 
> them
> - Or you configure different pools on the servers so that although 
> they serve the same subnet they serve non-overlapping pools and it 
> will be non-deterministic which server a client takes a lease from.
> In either case, if a server fails, the clients bound to it will 
> eventually time out on their leases and will either lose networking 
> or get a different address.
> 
> 
> I suggest you read the man pages and look up failover, and also find 
> a copy of The DHCP Handbook by Ralph Droms and Ted Lemon - this is 
> considered to the 'the bible' of DHCP and is both very readable and 
> very informative.
> 
> 
> >Can anyone please send me the actual configuration for the above
> >scenario
> 
> You mean, leave you nothing to do except take the credit ?
> 
> 
-- 
Douglas Power <dpower at fnb.co.za>
FNB

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