[Dnsmasq-discuss] slowing down dhcp

Rick Jones rick.jones2 at hpe.com
Fri Jun 24 00:45:31 BST 2016


On 06/23/2016 02:34 PM, Eric Johansson wrote:
> I have some really old ip phones (polycom ip 430).  they are sending
> lease requests but it ooks like they are not catching the reply.  I put
> dnsmasq on a vm (on a slower system) and the phone starts to catch the
> requests after 4-5 tries.  I'm interpreting this as phones that are too
> slow for the modern network
>
>   any idea on how I can slow down just the dhcp exchange to test out
> this conjecture?

Under Linux there is something called "netem" (network emulator) which 
can be pushed onto the stack as a tc qdisc to control bandwidth and 
delay among other things.  I've only used it "universally" rather than 
trying to slow-down just a specific traffic type, but I suspect it may 
be possible to do some filtering/marking/whatnot to get the DHCP traffic 
as the only traffic affected.

Under *BSD I think similar functionality can be found in something 
called "dummynet."

Of course, if you were to build dnsmasq from source, you could probably 
just put a sleep/usleep/whatnot somewhere in the reply path.

happy benchmarking,

rick jones




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