Dhcp load testing

Dave C Dhcp at gvtc.drakkar.org
Thu Oct 31 20:27:26 UTC 2019

That part about sending your logs elsewhere via syslog is extremely critical.

The leases file will be an append only operation and can handle a pretty hefty workload, as long 
as the diskio subsystem isn't also dragging attention to syslog writing to local disks several 
times for _every_ dhcp transaction.

Send syslog elsewhere and it should dramatically improve performance for you.

A trick I've done in the very distant past when disk speeds were horrible was to create a 
virtual disk in ram (ramdisk), let the leases file live there and once a minute or so, copy the 
leases file to a persistent disk.

I'd think that would only be needed for extremely busy systems. I've routinely managed leases 
for around 75k files on a low powered Linux VM... but only when I turned off local syslog :) If 
you needed to manage a half million or so, maybe a ramdisk might be needed... but at that point 
I'd start looking at lease times to reduce transaction cycles and whether it makes more sense to 
split the environment to multiple DHCP servers so that you don't have as many eggs in a single 
basket (or pair of baskets in an active/active configuration). I went from a pair of servers 
each handling 75k or so leases to 5 sets of paired active/active servers each handling about 1/4 
to 1/6 of what the two combined used to have.


On 10/30/19 20:02, Peter Yardley wrote:
> Take a look at …
> https://kb.isc.org/docs/aa-01283
> Major bottleneck is disk IO so try to speed that up (raid, flash etc). If using UNIX put the 
> leases file in a mount point with ‘noatime’ enabled. Send the logs to another server using syslog.
>  > On 31 Oct 2019, at 5:21 am, Kraishak Mahtha <kraishak.edu at gmail.com> wrote:
>  >
>  > Hi Everyone,
>  >
>  > I am using the isc dhcpd on my lab environment so before I use it to my workshop, I want to 
> try load test on it. I created the configuration with sufficient long pool, I tried running 
> perfdhcp tool for load testing as suggested in many google forums and I observed that at a 
> maximum of 10-14 transactions per second(tried with other different tools also), If I increase 
> load the packets are getting dropped, I don't think that is benchmark of ISC dhcp, can any one 
> has idea or any suggestions of how can i increase load handling capacity of the dhcpd service
>  > FYI: I diabled ping check
>  > Ping check false;
>  > Ping time out 0;
>  > The above two statements already added to my config file.
>  >
>  >
>  > Thanks
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