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

Fri Apr 28 22:36:02 BST 2017

On 27/04/17 22:02, 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?
> 
>

What's the interface/vlan configuration?
Where is the DHCP relay running and how is it configured?

Cheers,

Simon.