Watching performance on a DHCP Server

[Larry Apolonio]

Hi,

I would like your opinion and any recommendations for tweaking a DHCP 
server.

Here are some things I came accross in my research and testing:

Watch the CPU IO wait, if it starts going above 10% consider switching 
to a faster storage system or moving stuff into tmpfs.
If startup time exceeds 30 seconds (or whatever restart threshhold you 
are looking at) change the HASH size.
Changing the HASH size will change the DHCP renew times, but changing 
the amount of leasable IP addresses and %age of those IP addresses used 
does NOT change performance in renews.
Keeping your leasable IP's 60 to 80% full will provide better 
performance in 4 way handshakes than with a fairly empty lease file.

I've seen performance improve by both increasing and decreasing the hash 
size.  I'm currently running more tests to see what is going on.

Basically, I'm trying to determine, how hard a can push my existing DHCP 
server, what to watch for, when to add memory, change hash size, get a 
faster box or split the DHCP server into two.  Any comments would be 
greatly appreciated.

Larry Apolonio

Here's a chart of startup time in seconds.  (Hope it looks OK after I 
send it)

	  	IP Addresses in scope
Active Leases 	  	65534 	131070 	196605 	262140 	327675 	393210 
458745 	524280
0 	1 	1 	1 	1 	1 	1 	1 	1
1000 	1 	5 	14 	19 	23 	30 	34 	40
2000 	1 	10 	29 	37 	45 	60 	67 	79
3000 	1 	14 	44 	55 	68 	89 	102 	119
4000 	1 	20 	58 	74 	92 	119 	127 	161
5000 	1 	25 	72 	94 	105 	150 	172 	202
10000 	1 	53 	149 	193 	239 	308 	354 	419
20000 	1 	123 	314 	374 	513 	651 	764 	902
30000 	1 	208 	495 	660 	823 	1031 	1195 	1446
40000 	2 	200 	513 	704 	883 	1109 	1284 	1564
50000 	2 	178 	472 	685 	870 	1097 	1271 	1550