DHCP Server not able to handle the Traffic

Agarwal Vivek-RNGB36 RNGB36 at motorola.com
Sun Apr 26 12:17:29 UTC 2009



I ran the commands on the Server and I got the following results. Can
you please help me in pointing the root cause for packets getting


[root at ppdhcpsrv tmp]# vmstat

procs -----------memory---------- ---swap-- -----io---- --system--

 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy
id wa st

 1  1    124  62768 233924 2731988    0    0     3   125    1    0  1  2
83 14  0


[root at ppdhcpsrv tmp]# iostat

Linux 2.6.18-53.el5 (ppdhcpsrv.menawimax.net)   04/26/2009


avg-cpu:  %user   %nice %system %iowait  %steal   %idle

           1.33    0.00    1.85   13.63    0.00   83.19


Device:            tps   Blk_read/s   Blk_wrtn/s   Blk_read   Blk_wrtn

sda              74.02        24.29      1002.99  258459635 10670953860


[root at ppdhcpsrv tmp]# netstat -s


    1708302478 total packets received

    11 with invalid addresses

    952 forwarded

    0 incoming packets discarded

    1708269698 incoming packets delivered

    1795804172 requests sent out

    33283 reassemblies required

    16613 packets reassembled ok

    526 fragments received ok

    1052 fragments created


    6736222 ICMP messages received

    7 input ICMP message failed.

    ICMP input histogram:

        destination unreachable: 4169751

        timeout in transit: 246989

        echo requests: 2318982

        echo replies: 500

    4082493 ICMP messages sent

    0 ICMP messages failed

    ICMP output histogram:

        destination unreachable: 1763511

        echo replies: 2318982


    624 active connections openings

    696009 passive connection openings

    831 failed connection attempts

    154 connection resets received

    2 connections established

    132212788 segments received

    70887573 segments send out

    13902 segments retransmited

    0 bad segments received.

    4804 resets sent


    1560813436 packets received

    1762616 packets to unknown port received.

    6311155 packet receive errors

    1718724673 packets sent


    87 invalid SYN cookies received

    563 resets received for embryonic SYN_RECV sockets

    1 packets pruned from receive queue because of socket buffer overrun

    70 ICMP packets dropped because they were out-of-window

    129838 TCP sockets finished time wait in fast timer

    2 packets rejects in established connections because of timestamp

    118986 delayed acks sent

    17945 delayed acks further delayed because of locked socket

    Quick ack mode was activated 257 times

    8 times the listen queue of a socket overflowed

    8 SYNs to LISTEN sockets ignored

    11300 packets directly queued to recvmsg prequeue.

    3425 packets directly received from backlog

    66888 packets directly received from prequeue

    275171 packets header predicted

    1710 packets header predicted and directly queued to user

    121225308 acknowledgments not containing data received

    8742277 predicted acknowledgments

    4501 times recovered from packet loss due to SACK data

    Detected reordering 1 times using FACK

    Detected reordering 1 times using SACK

    Detected reordering 71 times using time stamp

    57 congestion windows fully recovered

    855 congestion windows partially recovered using Hoe heuristic

    198 congestion windows recovered after partial ack

    1568 TCP data loss events

    44 timeouts after SACK recovery

    2 timeouts in loss state

    6255 fast retransmits

    2828 forward retransmits

    372 retransmits in slow start

    1492 other TCP timeouts

    77 sack retransmits failed

    47 packets collapsed in receive queue due to low socket buffer

    272 DSACKs sent for old packets

    662 DSACKs received

    9 connections reset due to early user close

    584 connections aborted due to timeout







Vivek Aggarwal





-----Original Message-----
From: sthaug at nethelp.no [mailto:sthaug at nethelp.no] 
Sent: Sunday, April 26, 2009 11:57 AM
To: Agarwal Vivek-RNGB36
Cc: dhcp-users at lists.isc.org
Subject: Re: DHCP Server not able to handle the Traffic


> Iam using ISC-DHCP-3.0.5 installed on RHEL5


> When I take a tcpdump on the DHCP Interface; I saw around 1000 DHCP
Discovers at the interface but when I see /var/log/messages I can see
only around 500 DHCP DISCOVERs over there. 


> Can anyone help me in debugging that where are the discovers being
lost and how can I check resolve that


Start by looking at system load. Check to see if the operating system is

losing UDP packets (which could happen), and pay particular attention to

the disk I/O operations. DHCP is often disk I/O bound, and an SSD or a

RAID controller with battery backed cache may help.


Steinar Haug, Nethelp consulting, sthaug at nethelp.no

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.isc.org/pipermail/dhcp-users/attachments/20090426/dd2ba83c/attachment.html>

More information about the dhcp-users mailing list