Option 50 in failover mode

[Simon Hobson]

I wrote:

>Bear in mind that if you rely on each server having a separate pool 
>capable of serving the network (which incidentally is NOT failover), 
>then in the event of a server failing, all the clients using that 
>server will get new addresses which may or may not cause problems.

And your Dynamic DNS updates **WILL** break - that is guaranteed.

Client gets lease from server A

A gives out a lease and updates DNS with clients hostname & IP address.

B now dies.

Client carries on, and after a while attempts to renew it's lease. A 
doesn't respond, so eventually client braadcasts to find another 
server. B now responds.

B gives client a different address - so client changes address and 
all it's open sessions get broken.

B attempts to update DNS - but there are A and PTR records put there 
by A. B will **NOT** perform the update as it recognises that the 
entries currently in there are not "owned" by itself.

Client now has different IP address, but DNS entries point to old 
address. This will not change until A is brought back online, expires 
it's old leases, cleans up the DNS, AND the client renews again with 
B.

-- 
Simon Hobson

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