[Dnsmasq-discuss] default lease time for dhcp-host entries ?

Maule Mark mark_maule at yahoo.com
Mon Dec 16 21:00:17 GMT 2013


As an alternative to a fake tag to remove the empty field, would it work to declare a static dhcp-range in my configuration file to cover the addresses that are managed by the hostsfile?



On Monday, December 16, 2013 2:47 PM, Maule Mark <mark_maule at yahoo.com> wrote:
 
I don't think our client is asking for a lease time.  Or if it was, I would also expect it to make the request on the very first DHCPREQUEST, which gets the correct 1h lease.
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>The double comma is to establish a placeholder field where we can plug in an optional tag: field, which we do in certain situations to influence the next dhcp exchange for this id.  The program we use to manage this file rigidly expects each line to have the same number of fields if this optional tag exists or not..  I'll try putting a fake tag in that field and see if it solves the 2m lease time issue.
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>On Monday, December 16, 2013 2:28 PM, Simon Kelley <simon at thekelleys.org.uk> wrote:
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>On 16/12/13 19:36, Maule Mark wrote:
>>> I'm seeing an unexptected (to me) behavior when using a dnsmasq
>>> hostsfile and dhcp.  To start, my interface (pmi_if) is configured with
>>> a lease time of 1h (the default), and I have a blank hostsfile.
>>>
>>> dhcp-leasefile=/var/lib/axiom/dnsmasq_pmi.leases
>>> dhcp-hostsfile=/var/lib/axiom/dnsmasq_pmi_hostsfile
>>> dhcp-range=172.30.80.0,static,255.255.255.0
>>> dhcp-range=172.30.80.200,172.30.80.240,255.255.255.0
>>> dhcp-lease-max=255
>>> dhcp-option=option:dns-server,172.30.80.1
>>> dhcp-option=option:router,172.30.80.1
>>> dhcp-option=option:ntp-server,172.30.80.1,172.30.80.2,172.30.80.3
>>> dhcp-option=option:default-ttl,50
>>> dhcp-option=option:all-subnets-local,1
>>> dhcp-script=/var/lib/axiom/dhcp-script-pmi.sh
>>> dhcp-boot=/pds/pxe/pxelinux.0,172.30.80.1
>>>
>>> Clients boot and are assigned dhcp addresses as expected.  We have a
>>> program in our software stack that looks for heartbeat messages on this
>>> pmi_if, and when detected, constructs a hostsfile entry for the client
>>> that looks like this:
>>>
>>> [root at pilot2 axiom]# cat dnsmasq_pmi_hostsfile
>>> 00:21:28:A1:F3:F2,00:21:28:A1:F3:F3,,WN5080020001592690,172.30.80.128
>>> 00:21:28:A1:CA:3A,00:21:28:A1:CA:3B,,WN5080020001592691,172.30.80.129
>>>
>>> The clients are running udhcpc from busybox.
>>>
>>> Everything works as expected until the clients get toward the end of
>>> their 1h lease period at which point the clients start sending
>>> DHCPREQUEST requests.  It seems at this point, that the leases granted
>>> are now 120s.  Here's some syslog output showing the first DHCPREQUEST
>>> being sent about 55 minutes into the 1h initial lease.  Why did dnsmasq
>>> return a lease time of 12s in this case?
>>>
>>> 2013-12-16 19:33:42.253+00:00 pilot2 dnsmasq-dhcp[23916]: 208328817
>>> DHCPREQUEST(pmi_if) 172.30.80.129 00:21:28:a1:ca:3a
>>> 2013-12-16 19:33:42.253+00:00 pilot2 dnsmasq-dhcp[23916]: 208328817
>>> tags: known, pmi_if
>>> 2013-12-16 19:33:42.253+00:00 pilot2 dnsmasq-dhcp[23916]: 208328817
>>> DHCPACK(pmi_if) 172.30.80.129 00:21:28:a1:ca:3a WN5080020001592691
>>> 2013-12-16 19:33:42.253+00:00 pilot2 dnsmasq-dhcp[23916]: 208328817
>>> requested options: 1:netmask, 3:router, 6:dns-server, 12:hostname,
>>> 2013-12-16 19:33:42.253+00:00 pilot2 dnsmasq-dhcp[23916]: 208328817
>>> requested options: 15:domain-name, 28:broadcast, 42:ntp-server
>>> 2013-12-16 19:33:42.253+00:00 pilot2 dnsmasq-dhcp[23916]: 208328817
>>> bootfile name: /pds/pxe/pxelinux.0
>>> 2013-12-16 19:33:42.253+00:00 pilot2 dnsmasq-dhcp[23916]: 208328817
>>> server name: 172.30.80.1
>>> 2013-12-16 19:33:42.253+00:00 pilot2 dnsmasq-dhcp[23916]: 208328817 next
>>> server: 172.30.80.3
>>> 2013-12-16 19:33:42.253+00:00 pilot2 dnsmasq-dhcp[23916]: 208328817 sent
>>> size:  1 option: 53 message-type  5
>>> 2013-12-16 19:33:42.253+00:00 pilot2 dnsmasq-dhcp[23916]: 208328817 sent
>>> size:  4 option: 54 server-identifier  172.30.80.3
>>> 2013-12-16 19:33:42.253+00:00 pilot2 dnsmasq-dhcp[23916]: 208328817 sent
>>> size:  4 option: 51 lease-time  2m
>>> 2013-12-16 19:33:42.253+00:00 pilot2 dnsmasq-dhcp[23916]: 208328817 sent
>>> size:  4 option: 58 T1  56s
>>> 2013-12-16 19:33:42.253+00:00 pilot2 dnsmasq-dhcp[23916]: 208328817 sent
>>> size:  4 option: 59
 T2  1m41s
>>> 2013-12-16 19:33:42.253+00:00 pilot2 dnsmasq-dhcp[23916]: 208328817 sent
>>> size:  4 option:  1 netmask  255.255.255.0
>>> 2013-12-16 19:33:42.253+00:00 pilot2 dnsmasq-dhcp[23916]: 208328817 sent
>>> size:  4 option: 28 broadcast  172.30.80.255
>>> 2013-12-16 19:33:42.253+00:00 pilot2 dnsmasq-dhcp[23916]: 208328817 sent
>>> size:  5 option: 15 domain-name  axiom
>>> 2013-12-16 19:33:42.253+00:00 pilot2 dnsmasq-dhcp[23916]: 208328817 sent
>>> size: 18 option: 12 hostname  WN5080020001592691
>>> 2013-12-16 19:33:42.253+00:00 pilot2 dnsmasq-dhcp[23916]: 208328817 sent
>>> size: 20 option:209   70:78:65:6c:69:6e:75:78:2e:63:66:67:2f:64...
>>> 2013-12-16 19:33:42.253+00:00 pilot2 dnsmasq-dhcp[23916]: 208328817
 sent
>>> size:  4 option:208   f1:00:74:7e
>>> 2013-12-16 19:33:42.253+00:00 pilot2 dnsmasq-dhcp[23916]: 208328817 sent
>>> size: 12 option: 42 ntp-server  172.30.80.1, 172.30.80.2, 172.30.80.3
>>> 2013-12-16 19:33:42.253+00:00 pilot2 dnsmasq-dhcp[23916]: 208328817 sent
>>> size:  4 option:  3 router  172.30.80.1
>>> 2013-12-16 19:33:42.253+00:00 pilot2 dnsmasq-dhcp[23916]: 208328817 sent
>>> size:  4 option:  6 dns-server  172.30.80.1
>>>
>>>
>>> Is there a default lease time of 120s for client requests whose
>>> addresses which match a hoststfile entry?.
>>
>>No, there's no 120s default, but there is a 120s floor (ie no lease less 
>>the 120s will be issued).
>>
>>Note that the DHCP _client_ can ask for a particular lease time, it 
>>would be interesting to see if it's sending a lease-time option for 120s 
>>or less in the DHCPREQUEST packet.
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>>Another potential issue is your hostfile:
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>>00:21:28:A1:CA:3A,00:21:28:A1:CA:3B,,WN5080020001592691,172.30.80.129
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>>I've not looked, but the double comma may concievably confuse the parser 
>>such that it looks like a zero, which then gets interpreted as a lease 
>>time, and transformed to 120s by the floor.
>>
>>I think that is the most likely explanation.
>>
>>Cheers,
>>
>>Simon.
>>
>>
>>>
>>> thanks
>>> Mark
>>>
>>>
>>>
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>>
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