DHCP Drops Packets
Nathan McDavit-Van Fleet
nmcdavit at alcor.concordia.ca
Fri Nov 12 14:38:41 UTC 2010
Both you and Red DHCP and Bjarne are amazing. Thank you both so much. I can't believe it. I learned a big lesson today. A mix of elation and sadness. Our server was so chock full of synchronous logging and small caches.
I also noticed that there was these options as well
Is it worthwhile to change those, maybe instead of the TCP ones? Because the performance issue from Bjarne was modify tcp which is not part of DHCP correct (unless we're talking about fail over)?
net.ipv4.tcp_rmem = 4096 87380 16777216
net.ipv4.tcp_wmem = 4096 65536 16777216
Now I have to figure out how to make it permanent.
We almost lost the service to be placed on Windows. So I'm glad we avoided that.
Nathan Van Fleet
Network Assessment and Integration
IITS Concordia University
(514) 848-2424 Extension:5434
> -----Original Message-----
> From: dhcp-users-bounces+nmcdavit=alcor.concordia.ca at lists.isc.org
> [mailto:dhcp-users-bounces+nmcdavit=alcor.concordia.ca at lists.isc.org]
> On Behalf Of Red DHCP
> Sent: Thursday, November 11, 2010 5:27 PM
> To: Users of ISC DHCP
> Subject: Re: DHCP Drops Packets
> try to set your dhcp logs to asynchronous mode (you need to edit the
> syslog config and restart syslogd process), this can increase your dhcp
> server performance
> On Thu, 2010-11-11 at 16:44 -0500, Nathan McDavit-Van Fleet wrote:
> > Hello All,
> > For some reason it appears as if our DHCP server 4.1.2 is not
> > responding to packets. We Wiresharked in front of the DHCP server and
> > saw that ~10 Discover packets were going into the server.
> > Unfortunately only one of those packets made it to the DHCP log
> > itself. We’ve had similar issues with DHCPRequest packets as well.
> > We’ve been seeing a big delay for clients trying to get an IP
> > Is this to do with the load of on the server itself? I haven’t found
> > dependable recommendation for load averages, but for example our
> > leases file is 4.1MB and our lease time is 3600 seconds with about
> > 3000 users or so.
> > I also tcpdump’d the server and at least MORE of the packets made it
> > to the interface than made it to DHCPD. I disabled iptables, added
> > 255.255.255.255 to my hosts file and verified SELinux had the
> > exceptions needed.
> > Past that I don’t know where to turn. Hopefully someone here has a
> > suggest.
> > Thanks,
> > -Nathan
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