[Dnsmasq-discuss] Disappearing hosts from local DNS resolution

Eric Thibodeau kyron at neuralbs.com
Tue Oct 7 16:58:39 BST 2008


richardvoigt at gmail.com wrote:
>> Nope, seems dhcpcd is not requesting a renew of the lease at 1/2 time as
>> it should (IIRC). http://wiki.neuralbs.com/~kyron/DHCP_reqs_tb17 contains
>> a grep of the DHCP activity from the disappearing nodes int
>> /var/log/messages.
>>     
>
> Can you get a client-side log, or even better packet capture?
> DISCOVER and RENEW requests may look different enough to match
> firewall rules differently.  For example, DISCOVER sent to broadcast
> address and RENEW sent unicast.
>   
Oct  7 11:50:52 thinkbig16 dhcpcd[29651]: eth0: sending signal 14 to pid 
21865
Oct  7 11:50:52 thinkbig16 dhcpcd[21865]: eth0: received SIGALRM, 
renewing lease
Oct  7 11:50:52 thinkbig16 dhcpcd[21865]: eth0: renewing lease of 10.0.1.136
Oct  7 11:50:52 thinkbig16 dhcpcd[21865]: eth0: NAK: lease not found 
from 10.0.1.129
Oct  7 11:50:52 thinkbig16 dhcpcd[29652]: eth0: 
/lib/dhcpcd/dhcpcd-run-hooks: Network is unreachable
Oct  7 11:50:53 thinkbig16 dhcpcd[21865]: eth0: broadcasting for a lease
Oct  7 11:50:53 thinkbig16 dhcpcd[21865]: eth0: offered 10.0.1.136 from 
10.0.1.136 `boothost'
Oct  7 11:50:53 thinkbig16 dhcpcd[21865]: eth0: ignoring offer of 
10.0.1.136 from 10.0.1.136 `boothost'
Oct  7 11:50:53 thinkbig16 dhcpcd[21865]: eth0: acknowledged 10.0.1.136 
from 10.0.1.136 `boothost'
Oct  7 11:50:53 thinkbig16 dhcpcd[21865]: eth0: checking 10.0.1.136 is 
available on attached networks
Oct  7 11:50:59 thinkbig16 dhcpcd[21865]: eth0: leased 10.0.1.136 for 
43200 seconds

So the lease time is explicitly received as being 12h (which is correct) 
but the " eth0: offered 10.0.1.136 from 10.0.1.136 `boothost' " has got 
me frowning... (note that `boothost' is defined in the config pasted below)

The tcpdump file is available at: 
http://wiki.neuralbs.com/~kyron/dhcpout_tb16 sorry for the net chatter 
but you get it all there ;)
>>> What does your network topology look like? Are you using DHCP relays
>>> and/or a not-fully-routed IP network? It's possiblr for hosts to be able
>>> to get a network, but not renew it under some circumstances.
>>>       
Ok at the risk of being flamed about network topology, I have a hacked 
up setup but it shouldn't impact DHCP IMHO (I'm emulating NIC bonding 
through IP masking).

Here is the setup:

http://wiki.neuralbs.com/~kyron/HyperTransport/ClusterNetDiagram.png

Here is the config file (sourced by dnsmasq.conf)
eric at headless ~/1_Files/1_ETS/1_Maitrise/Code/pvq $ cat 
/etc/dnsmasq.AthlonXP_All.conf
# On force le broadcast à 10.0.1.255
dhcp-option=28,10.0.1.255

#The group name,address range and lease time:
dhcp-range=AthlonXP_1,10.0.1.10,10.0.1.126,255.255.255.0,12h
# The GROUP_NAME's,option 3:default Gateway (if you really need this, 
nodes shouldn't require routed access):
dhcp-option=AthlonXP,3,10.0.1.1
# The GROUP_NAME's, option 42:time server address:
dhcp-option=AthlonXP_1,42,10.0.1.1
# This is required for PXE booting
dhcp-boot=net:AthlonXP_1,/pxelinux.0,boothost,10.0.1.1
# As can be seen in the dnsmasq.conf, this option is not guaranteed to 
work (DN search order)
dhcp-option=AthlonXP_1,119,cluster.local
# Domain DNS name
dhcp-option=15,cluster.local
# NIS domain
dhcp-option=40,cluster.local

# Now for the host listing, format is:
# dhcp-host=MACADDRESS,net:GROUP_NAME,NODE_NAME,IP_ADDRESS
dhcp-host=00:01:03:df:ca:44,net:AthlonXP_1,thinkbig1,10.0.1.11
dhcp-host=00:01:03:DF:C6:38,net:AthlonXP_1,thinkbig2,10.0.1.12
dhcp-host=00:01:03:DF:D3:30,net:AthlonXP_1,thinkbig3,10.0.1.13
dhcp-host=00:01:03:DF:D3:08,net:AthlonXP_1,thinkbig4,10.0.1.14
dhcp-host=00:01:03:DF:D3:01,net:AthlonXP_1,thinkbig5,10.0.1.15
dhcp-host=00:01:03:DF:CA:3B,net:AthlonXP_1,thinkbig6,10.0.1.16
dhcp-host=00:04:75:C2:21:14,net:AthlonXP_1,thinkbig7,10.0.1.17
dhcp-host=00:01:03:DF:CA:46,net:AthlonXP_1,thinkbig8,10.0.1.18
dhcp-host=00:01:03:de:5f:2e,net:AthlonXP_1,thinkbig9,10.0.1.19

#
# The group name,address range and lease time:
dhcp-range=AthlonXP_2,10.0.1.130,10.0.1.254,255.255.255.0,12h
# The GROUP_NAME's,option 3:default Gateway (if you really need this, 
nodes shouldn't require routed access):
dhcp-option=AthlonXP_2,3,10.0.1.129
# The GROUP_NAME's, option 42:time server address:
dhcp-option=AthlonXP_2,42,10.0.1.129
# This is required for PXE booting
dhcp-boot=net:AthlonXP_2,/pxelinux.0,boothost,10.0.1.129
# As can be seen in the dnsmasq.conf, this option is not guaranteed to 
work (DN search order)
#dhcp-option=AthlonXP_2,119,cluster.local
# Now for the host listing, format is:
# dhcp-host=MACADDRESS,net:GROUP_NAME,NODE_NAME,IP_ADDRESS

dhcp-host=00:01:03:DE:B5:C3,net:AthlonXP_1,thinkbig10,10.0.1.130
dhcp-host=00:01:03:DE:B6:AE,net:AthlonXP_1,thinkbig11,10.0.1.131
dhcp-host=00:04:75:AA:36:5B,net:AthlonXP_1,thinkbig12,10.0.1.132
dhcp-host=00:01:03:DF:CA:42,net:AthlonXP_2,thinkbig13,10.0.1.133
dhcp-host=00:01:03:DE:B5:C2,net:AthlonXP_2,thinkbig14,10.0.1.134
dhcp-host=00:01:03:24:E9:3B,net:AthlonXP_2,thinkbig15,10.0.1.135
dhcp-host=00:04:75:EC:33:47,net:AthlonXP_2,thinkbig16,10.0.1.136
dhcp-host=00:04:75:EC:4E:F2,net:AthlonXP_2,thinkbig17,10.0.1.137
#dhcp-host=00:04:75:EC:4E:CF,net:AthlonXP_2,thinkbig18,10.0.1.138

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