DHCP server answers with delay

[Peter Capriccio]

On 4/3/2014  Denis Taranushin wrote:
> Date: Thu, 03 Apr 2014 10:59:47 +0600
> From: Denis Taranushin<tda at suttk.ru>
> To:dhcp-users at lists.isc.org
> Subject: DHCP server answers with delay
> Message-ID:<533CEAC3.4020801 at suttk.ru>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
> Hello, All
>
> We have trouble with DHCP. namely the DHCP server answers with delay.
> Sometimes the Server answers on 2th or 3th "Discover"
> In this time a Client sends some "Discover"s and the server answers each
> of them.
> So in final the Client receives 2-3 "Offers" of IP, and accepts the last
> one.
>
> It makes impossible to work billing because the billing does session by
> the first "Discover" and the second and each next will be forbidden.
>
> Why the server answers in 4 secs after the first "Discover"?
>
> tcpdump on server:
> 1335	2014-04-02 11:04:41.173969	10.0.0.1	10.0.0.13	DHCP	378	DHCP
> Discover - Transaction ID 0x21fe4bf0
>
> 2344	2014-04-02 11:04:44.168945	10.0.0.1	10.0.0.13	DHCP	378	DHCP
> Discover - Transaction ID 0x21fe4bf0
>
> 2554	2014-04-02 11:04:45.171448	10.0.0.13	10.0.0.1	DHCP	369	DHCP Offer
>     - Transaction ID 0x21fe4bf0
>
> 2559	2014-04-02 11:04:45.196749	10.0.0.1	10.0.0.13	DHCP	402	DHCP Request
>    - Transaction ID 0x21fe4bf0
>
> 2562	2014-04-02 11:04:45.199567	10.0.0.13	10.0.0.1	DHCP	369	DHCP ACK
>     - Transaction ID 0x21fe4bf0
>
> 3813	2014-04-02 11:04:48.714916	10.0.0.1	10.0.0.13	DHCP	373	DHCP Inform
>     - Transaction ID 0x8b4c15cc
>
> 3819	2014-04-02 11:04:48.719283	10.0.0.13	10.0.0.247	DHCP	342	DHCP ACK
>       - Transaction ID 0x8b4c15cc
>
>
> Unfortunately I can't provide the config because it is enormous.
>
> Some ideas?
Could this be possibly related to a "ping-check", assuming that it is 
enabled, to the client? I have some clients that don't follow the spec 
and hold on to their current IP address when doing a discover, so the 
ping check is positive (server can ping the client IP address in the 
lease database), so the server abandons the lease, and during which 
time, the client sends multiple discovers (maybe check the logs for 
abandoned leases?) -- just a WAG...

Pete C.

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