DHCP transactions per second
Simon Hobson
dhcp1 at thehobsons.co.uk
Mon Jun 18 08:35:56 UTC 2007
Ian Anderson wrote:
>With further investigation it appears that we are getting multiple
>requests for each client. We have several ip helper addresses (foundry
>switchs) in our network, and I believe we may have a misconfiguration
>somewhere.
>
>For example, if a client has never powered up on our network before it
>performs the typical DISCOVER/OFFER/REQUEST/ACK Because all of those
>are broadcast the dhcp server is receiving the client messages 4 times.
>(and responding 4 times as well) 4 DISCOVERS / 4 REQUESTS. I know dhcp
>can cope with this, and the server will ACK the first REQUEST it
>receives from any given client. Even though dhcp can handle this, is
>this a significant source of additional load on the server?
More or less, each request adds one unit of extra work.
>Are duplicate broadcasts treated any differently by dhcp than receiving just
>one broadcast?
No
>Or in other words, does dhcp know the difference between a normal
>broadcast and one that is a duplicate?
How can it ? They are simply relayed packets and will be identical
other than the GIAddr - there is nothing to say "this is a duplicate".
>I would imagine in order to get an accurate representation of your dhcp
>servers transactions per second you would need to fix whatever is
>causing the duplicate messages.
Yes - it would help !
However, as you say, these extra packets don't cause any problems
other than the extra load - except ...
IIRC there is or was a problem related to multiple relayed requests
that come in closely spaced. I can't remember what it was now !
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