[Dnsmasq-discuss] bug:DHCP Relay not responding with DHCP OFFER.

Jason Kary jkary_98 at yahoo.com
Mon May 1 21:31:17 BST 2017


Hi Dan,

Thank you for the update.  This appears to have resolved my issue.

Take Care
Jason

> On May 1, 2017, at 2:35 PM, Dan Sneddon <dsneddon at redhat.com> wrote:
> 
> Your routing table is wrong. You have both 10.168.101.0/24 and
> 10.168.102.0/24 both set up as local subnets (see the 0.0.0.0 gateway).
> The remote subnet should be routed through the local router, so your
> route would appear something like this:
> 
> 10.168.101.0  0.0.0.0   255.255.255.0   U         0 0      0 ens160
> 10.168.102.0  10.168.101.1   255.255.255.0   U       0 0      0 ens160
> 
> -- 
> Dan Sneddon         |  Senior Principal Software Engineer
> dsneddon at redhat.com |  redhat.com/openstack
> dsneddon:irc        |  @dxs:twitter
> 
> On 04/27/2017 02:02 PM, Jason Kary wrote:
>> Hi Folks,
>> 
>> I have a basic setup for DHCP relay across VLANS in DNSMASQ.  
>> 
>> My configuration file looks like: 
>> 
>> 
>>    bogus-priv
>>    interface=ens160
>>    log-dhcp
>>    dhcp-range=10.168.102.100,10.168.102.150,255.255.255.0,12h
>> 
>> 
>> The client and server are running on a VMs in separate VLANS.  DHCP
>> requests appear to be coming across:
>> 
>> 
>>    root at DHCP-UBUNTU-SERVER:~# tcpdump -i ens160 port 67 or port 68 -n
>>    tcpdump: verbose output suppressed, use -v or -vv for full protocol
>>    decode
>>    listening on ens160, link-type EN10MB (Ethernet), capture size
>>    262144 bytes
>>    03:58:40.966944 IP 10.168.102.1.67 > 10.168.101.20.67: BOOTP/DHCP,
>>    Request from 00:0c:29:65:e0:ea, length 322
>>    03:58:46.487767 IP 10.168.102.1.67 > 10.168.101.20.67: BOOTP/DHCP,
>>    Request from 00:0c:29:65:e0:ea, length 322
>>    03:58:54.424895 IP 10.168.102.1.67 > 10.168.101.20.67: BOOTP/DHCP,
>>    Request from 00:0c:29:65:e0:ea, length 322
>>    03:59:07.795712 IP 10.168.102.1.67 > 10.168.101.20.67: BOOTP/DHCP,
>>    Request from 00:0c:29:65:e0:ea, length 322
>>    03:59:19.196022 IP 10.168.102.1.67 > 10.168.101.20.67: BOOTP/DHCP,
>>    Request from 00:0c:29:65:e0:ea, length 322
>> 
>>    root at DHCP-UBUNTU-SERVER:~# iptables -L
>>    Chain INPUT (policy ACCEPT)
>>    target     prot opt source               destination
>> 
>>    Chain FORWARD (policy ACCEPT)
>>    target     prot opt source               destination
>> 
>>    Chain OUTPUT (policy ACCEPT)
>>    target     prot opt source               destination
>>    root at DHCP-UBUNTU-SERVER:~#
>> 
>> 
>> The syslog log indicates the DCHP OFFERS are ‘supposed’ to be going out
>> however nothing is seen on the wire.
>> 
>> 
>>    Apr 27 04:03:26 DHCP-UBUNTU-SERVER dnsmasq-dhcp[17767]: 1121794364
>>    available DHCP range: 10.168.102.100 -- 10.168.102.150
>>    Apr 27 04:03:29 DHCP-UBUNTU-SERVER dnsmasq-dhcp[17767]: 1121794364
>>    DHCPDISCOVER(ens160) 00:0c:29:65:e0:ea
>>    Apr 27 04:03:29 DHCP-UBUNTU-SERVER dnsmasq-dhcp[17767]: 1121794364
>>    tags: ens160
>>    Apr 27 04:03:29 DHCP-UBUNTU-SERVER dnsmasq-dhcp[17767]: 1121794364
>>    DHCPOFFER(ens160) 10.168.102.128 00:0c:29:65:e0:ea
>>    Apr 27 04:03:29 DHCP-UBUNTU-SERVER dnsmasq-dhcp[17767]: 1121794364
>>    requested options: 1:netmask, 28:broadcast, 2:time-offset,
>>    121:classless-static-route,
>>    Apr 27 04:03:29 DHCP-UBUNTU-SERVER dnsmasq-dhcp[17767]: 1121794364
>>    requested options: 15:domain-name, 6:dns-server, 12:hostname,
>>    Apr 27 04:03:29 DHCP-UBUNTU-SERVER dnsmasq-dhcp[17767]: 1121794364
>>    requested options: 40:nis-domain, 41:nis-server, 42:ntp-server,
>>    Apr 27 04:03:29 DHCP-UBUNTU-SERVER dnsmasq-dhcp[17767]: 1121794364
>>    requested options: 26:mtu, 119:domain-search, 3:router,
>>    121:classless-static-route,
>>    Apr 27 04:03:29 DHCP-UBUNTU-SERVER dnsmasq-dhcp[17767]: 1121794364
>>    requested options: 249, 33:static-route, 252, 42:ntp-server
>>    Apr 27 04:03:29 DHCP-UBUNTU-SERVER dnsmasq-dhcp[17767]: 1121794364
>>    next server: 10.168.101.20
>>    Apr 27 04:03:29 DHCP-UBUNTU-SERVER dnsmasq-dhcp[17767]: 1121794364
>>    sent size:  1 option: 53 message-type  2
>>    Apr 27 04:03:29 DHCP-UBUNTU-SERVER dnsmasq-dhcp[17767]: 1121794364
>>    sent size:  4 option: 54 server-identifier  10.168.101.20
>>    Apr 27 04:03:29 DHCP-UBUNTU-SERVER dnsmasq-dhcp[17767]: 1121794364
>>    sent size:  4 option: 51 lease-time  12h
>>    Apr 27 04:03:29 DHCP-UBUNTU-SERVER dnsmasq-dhcp[17767]: 1121794364
>>    sent size:  4 option: 58 T1  6h
>>    Apr 27 04:03:29 DHCP-UBUNTU-SERVER dnsmasq-dhcp[17767]: 1121794364
>>    sent size:  4 option: 59 T2  10h30m
>>    Apr 27 04:03:29 DHCP-UBUNTU-SERVER dnsmasq-dhcp[17767]: 1121794364
>>    sent size:  4 option:  1 netmask  255.255.255.0
>>    Apr 27 04:03:29 DHCP-UBUNTU-SERVER dnsmasq-dhcp[17767]: 1121794364
>>    sent size:  4 option: 28 broadcast  10.168.102.255
>>    Apr 27 04:03:29 DHCP-UBUNTU-SERVER dnsmasq-dhcp[17767]: 1121794364
>>    sent size:  4 option:  3 router  10.168.102.1
>>    Apr 27 04:03:29 DHCP-UBUNTU-SERVER dnsmasq-dhcp[17767]: 1121794364
>>    sent size:  4 option:  6 dns-server  10.168.101.20
>>    Apr 27 04:03:29 DHCP-UBUNTU-SERVER dnsmasq-dhcp[17767]: 1121794364
>>    sent size: 20 option: 82 agent-id
>>     01:0a:01:08:00:06:00:4c:4f:2a:00:2f:02:06…
>> 
>> 
>> I’ve been trying to trace this issue and it is like the sendmsg system
>> call is not working properly.  I believe routing is setup properly on
>> the DHCP server.
>> 
>>    root at DHCP-UBUNTU-SERVER:~# netstat -nr
>>    Kernel IP routing table
>>    Destination     Gateway         Genmask         Flags   MSS Window
>>     irtt Iface
>>    0.0.0.0         172.31.13.1     0.0.0.0         UG        0 0      
>>       0 ens192
>>    10.168.101.0    0.0.0.0         255.255.255.0   U         0 0      
>>       0 ens160
>>    10.168.102.0    0.0.0.0         255.255.255.0   U         0 0      
>>       0 ens160
>>    172.31.13.0     0.0.0.0         255.255.255.0   U         0 0      
>>       0 ens192
>>    root at DHCP-UBUNTU-SERVER:~#
>> 
>> Can anyone seen something obvious that I am doing wrong?
>> 
>> Take Care
>> Jason
>> 
>> 
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>> 
> 
> 
> 
> 
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