DHCP transactions per second

[Ian Anderson]

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?  Are 
duplicate broadcasts treated any differently by dhcp than receiving just 
one broadcast?  Or in other words, does dhcp know the difference between 
a normal broadcast and one that 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. 


Bruce Hudson wrote:
>> Both DHCPDISCOVER and DHCPREQUEST values compute to the same tps. Could 
>> one conclude that when attempting to compute dhcp tps, you only need to 
>> take DHCPDISCOVER 4 way handshakes into account?  
>>     
>
>     Dangerous assumption. It is a coincidence. The 2:1 ratio of discovery
> to renewal ignores such things as DHCPINFORM packets; something we have
> seen Vista make heavy use of. The 2:1 ration of the number of requests
> assumes that everybody turns their computers on in the morning and off in
> the evening and never reboots during the day. It also assumes that lease
> times are 24 hours. 
>
>     The real numbers will be a mixture of discovers and renewals but what
> the balance is between them will depend on your population. We see 
> different "cultures" that affect the balance just within various parts of
> the university. 
>
>     In any case, even with minimal servers you can expect to handle at
> least 20 transactions per second so you have much room for error.
> --
> Bruce A. Hudson				| Bruce.Hudson at Dal.CA
> UCIS, Networks and Systems		|
> Dalhousie University			|
> Halifax, Nova Scotia, Canada		| (902) 494-3405
>
>