[Ext] DHCPREQUEST flooding

Jim Glassford jmglass at iup.edu
Thu May 5 15:08:08 UTC 2016


Hi Alex,

I blame poor IP stacks on the client device.
We get hammered by some wired game systems, mobile devices and once in a 
while a printer. Printers I get them to review/update drivers or we do a 
hard code on it, problem games systems and mobile devices are mostly 
student devices so just live with the DHCPREQUESTS until they upgrade or 
graduate. Not so easy for you.

best!
jim



On 5/5/2016 10:40 AM, Alex Moen wrote:
> I am running a 4.2.5 ISC DHCP server (up-to-date via Centos 7 
> repository) for our ISP business.  We have around 7000 subscribers; 
> most with an el-cheapo router, a few with no router at all.  Most of 
> our customers are using a variant of Linksys router (Linksys, 
> Cisco-Linksys, Belkin, etc) because that is what we provide if they 
> ask for a router. However, this issue is not only a Linksys issue, as 
> we are also seeing PCs exhibiting the same behavior.
>
> The issue is that we have a fairly large number of devices (around 
> 300) that are issuing DHCPREQUESTs at extremely short intervals (the 
> worst, a few second apart).  In the last 6 hours, some of these 
> devices have REQUESTed over 2000 times.  They are all being ACKed.
>
> Is this a common problem that everyone sees, or do I have a config 
> issue?  This has actually been going on for a long, long time, and I 
> am just tired of the large log file sizes.  Since we're an ISP, we 
> have to keep our logs for a few years time, so the log file size can 
> become an issue.
>
> A typical network stanza looks like:
>
>         subnet 76.10.94.0 netmask 255.255.254.0 {
>         pool {
>               authoritative;
>               range 76.10.94.20 76.10.95.200;
>               min-lease-time 129600;
>               max-lease-time 259200;
>               default-lease-time 259200;
>               option subnet-mask 255.255.254.0;
>               option broadcast-address 76.10.95.255;
>               option routers 76.10.94.1;
>               }
>         }
>
> Thanks for any input!!
>
> Alex
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