Too long interval between DHCPDISCOVER messages

Mikael Svantesson XM (AS/EAB) mikael.xm.svantesson at ericsson.com
Thu Jun 19 10:40:59 UTC 2008


Hi,

I'm currently working on a product which uses dhclient 3.0.5 as the DHCP
client.
I know it's old but unfortunately, we can't update it, applying patches
on the other hand may be acceptable depending on the situation.

For some time ago we were requested to do a DHCP conformance test with
Ixia's testing tool (IxANVL, I believe).

One of the tests which failed and we are considering important for us is
 that there is an interval of 11 seconds (10.5xxxx to be precise)
between two DHCPDISCOVER messages while IxANVL states the following:

   The client MUST adopt a retransmission strategy that incorporates a
   randomized exponential backoff algorithm to determine the delay
   between retransmissions

   RFC 2131 Section 4.1 Page 24 'Constructing and sending DHCP
   messages'

   In the RFC, it is quoted, the time interval between two DHCPDISCOVER
   message should be 4 seconds randomised value chosen between range
   +/-1

However, reading the RFC one can read this:

   The delay between retransmissions SHOULD be
   chosen to allow sufficient time for replies from the server to be
   delivered based on the characteristics of the internetwork between
   the client and the server.  For example, in a 10Mb/sec Ethernet
   internetwork, the delay before the first retransmission SHOULD be 4
   seconds randomized by the value of a uniform random number chosen
   from the range -1 to +1.

Is this a case where Ixia may have interprented the RFC wrong? I think
it might be...

But, whatever the reason is, changing the "initial-interval"
configuration option (which controls this interval as I understand) does
not change the 11 seconds interval. We have tried to set it to various
values but see no difference.
As we think this might be one of the things slowing our boot time down,
we probably would want a lower interval than 11 seconds however.

Thank you!

Regards,
Mikael


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