dhcpd capacity

Frank Bulk - iNAME frnkblk at iname.com
Wed Nov 7 02:05:36 UTC 2007


Have you turned on debugging on your CMTS to make see if the DHCP replies
are at least getting processed there?  Have you been telneted into your CM
on the LAN port side to see if it's getting the DHCP replies, or if there is
any more information?  Ideally you would have a DOCSIS protocol analyzer
from Sigtek.

Frank

-----Original Message-----
From: dhcp-users-bounce at isc.org [mailto:dhcp-users-bounce at isc.org] On Behalf
Of fadey
Sent: Tuesday, November 06, 2007 6:06 PM
To: dhcp-users at isc.org
Subject: Re: dhcpd capacity

Thanks for your reply
I've set
ping-check off;
in the config file. Also now I'm running dhcpd with
dhcpd -d -f 2>/dev/null (I guess this way it will not write to disk on
every request). Yet what I see from a tcpdump trace is that the
situation has not improved:

0:42:31.941360 IP 192.168.0.2.67 > 10.2.0.1.67: BOOTP/DHCP, Reply,
length: 328
00:42:31.990506 IP 10.0.0.1.67 > 192.168.0.2.67: BOOTP/DHCP, Request
from 00:0f:21:e7:50:bd, length: 436
00:42:32.055564 IP 10.0.0.1.67 > 192.168.0.2.67: BOOTP/DHCP, Request
from 00:14:f8:8d:1c:70, length: 512
00:42:32.311609 IP 10.2.0.1.67 > 192.168.0.2.67: BOOTP/DHCP, Request
from 00:16:17:aa:82:7a, length: 320
00:42:32.374133 IP 192.168.0.2.67 > 10.0.0.1.67: BOOTP/DHCP, Reply,
length: 300
00:42:32.672425 IP 10.0.0.1.67 > 192.168.0.2.67: BOOTP/DHCP, Request
from 00:14:f8:8d:1c:64, length: 512
00:42:32.779738 IP 10.0.0.1.67 > 192.168.0.2.67: BOOTP/DHCP, Request
from 00:14:f8:8d:1a:34, length: 512
00:42:33.004367 IP 10.0.0.1.67 > 192.168.0.2.67: BOOTP/DHCP, Request
from 00:14:f8:8d:1a:44, length: 524
00:42:33.108238 IP 10.0.0.1.67 > 192.168.0.2.67: BOOTP/DHCP, Request
from 00:14:f8:8d:1a:2c, length: 512
00:42:33.281421 IP 10.0.0.1.67 > 192.168.0.2.67: BOOTP/DHCP, Request
from 00:14:f8:8d:1b:e8, length: 524
00:42:33.621956 IP 192.168.0.2.67 > 10.0.0.1.67: BOOTP/DHCP, Reply,
length: 305
00:42:33.711499 IP 10.0.0.1.67 > 192.168.0.2.67: BOOTP/DHCP, Request
from 00:14:f8:8d:1a:1c, length: 512
00:42:33.904487 IP 10.0.0.1.67 > 192.168.0.2.67: BOOTP/DHCP, Request
from 00:11:e6:f2:39:26, length: 424
00:42:34.010164 IP 10.0.0.1.67 > 192.168.0.2.67: BOOTP/DHCP, Request
from 00:11:e6:f2:3c:cc, length: 424
00:42:34.037943 IP 192.168.0.2.67 > 10.0.0.1.67: BOOTP/DHCP, Reply,
length: 305
00:42:34.070474 IP 10.0.0.1.67 > 192.168.0.2.67: BOOTP/DHCP, Request
from 00:14:f8:8d:1c:68, length: 512
00:42:34.153420 IP 10.0.0.1.67 > 192.168.0.2.67: BOOTP/DHCP, Request
from 00:14:f8:8d:1c:44, length: 512
00:42:34.194339 IP 10.0.0.1.67 > 192.168.0.2.67: BOOTP/DHCP, Request
from 00:14:f8:8d:1a:48, length: 524
00:42:34.199977 IP 10.0.0.196.1055 > 192.168.0.2.69:  35 RRQ
"SA-EPX2203-VODA-BASICA.cfg" octet
00:42:34.418991 IP 10.0.0.1.67 > 192.168.0.2.67: BOOTP/DHCP, Request
from 00:0f:21:e7:4f:db, length: 436
00:42:34.444522 IP 10.0.0.1.67 > 192.168.0.2.67: BOOTP/DHCP, Request
from 00:0e:5c:a9:5e:a0, length: 523
00:42:34.481865 IP 10.0.0.1.67 > 192.168.0.2.67: BOOTP/DHCP, Request
from 00:11:e6:f1:eb:6a, length: 436
00:42:34.649512 IP 10.0.0.1.67 > 192.168.0.2.67: BOOTP/DHCP, Request
from 00:0f:21:e7:51:99, length: 436
00:42:34.696330 IP 10.0.0.1.67 > 192.168.0.2.67: BOOTP/DHCP, Request
from 00:11:e6:f1:ea:ea, length: 424
00:42:34.761267 IP 10.0.0.1.67 > 192.168.0.2.67: BOOTP/DHCP, Request
from 00:0e:5c:a9:5e:b2, length: 523
00:42:34.985876 IP 10.0.0.1.67 > 192.168.0.2.67: BOOTP/DHCP, Request
from 00:11:e6:f1:eb:74, length: 424
00:42:35.099862 IP 192.168.0.2.67 > 10.2.0.1.67: BOOTP/DHCP, Reply,
length: 300
00:42:35.233276 IP 10.0.0.1.67 > 192.168.0.2.67: BOOTP/DHCP, Request
from 00:0f:21:e7:4f:23, length: 436
00:42:35.595500 IP 10.0.0.1.67 > 192.168.0.2.67: BOOTP/DHCP, Request
from 00:14:f8:8d:1c:78, length: 512
00:42:35.702524 IP 10.2.0.1.67 > 192.168.0.2.67: BOOTP/DHCP, Request
from 00:14:f8:8d:1a:22, length: 484
00:42:35.818158 IP 10.2.0.1.67 > 192.168.0.2.67: BOOTP/DHCP, Request
from 00:0e:5c:a6:68:7c, length: 300
00:42:35.991982 IP 10.0.0.1.67 > 192.168.0.2.67: BOOTP/DHCP, Request
from 00:0f:21:e7:50:bd, length: 436
00:42:36.138845 IP 192.168.0.2.67 > 10.0.0.1.67: BOOTP/DHCP, Reply,
length: 300
00:42:36.281502 IP 10.0.0.1.67 > 192.168.0.2.67: BOOTP/DHCP, Request
from 00:14:f8:8d:1b:e8, length: 524
00:42:36.709991 IP 10.0.0.1.67 > 192.168.0.2.67: BOOTP/DHCP, Request
from 00:14:f8:8d:1c:5c, length: 512
00:42:36.776847 IP 192.168.0.2.67 > 10.2.0.1.67: BOOTP/DHCP, Reply,
length: 329


Just wondering if anyone has experienced this before. I've got just 200
cable modems in my network. I guess there are networks MUCH bigger then
that which are using isc dhcpd


> fadey wrote:
>
> >I'm experiencing a problem with dhcpd in a cable network. Once cable
> >modems are reset (I have about 200), a storm of packets is flooding
> >dhcpd and it can't serve the networking  information to all of cable
> >modems at once. For about every 5 DISCOVERs I see 1 OFFER (with
> >tcpdump). So, I guess that either some OFFERSs are being dropped or by
> >the time they reach a cable modem a timeout opccurs.
> >I'm wondering if there is something in the configuration that can
> >influence the responce time of dhcpd.
>
> Check the archives, there's been a number of threads about server
> performance over the last few months. A few tips :
>
> ping-before-offer : you can turn this off
>
> logging : is syslog configured to write logs synchronously ? If so,
> then this slows things down quite a bit (every log created results in
> a disk write). Setting this to async helps quite a bit.
>
> Also, some people have experimented with putting various things on
> ram disk - but it may not be safe against reboots.
>
>
>





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