[Dnsmasq-discuss] No DHCP on eth1

Eldon Ziegler eldonz at atlanticdb.com
Wed Nov 17 10:43:48 GMT 2010


We are downsizing an app that runs on multiple servers onto a single
server but are not getting DHCP responses from dnsmasq on eth1. It works
correctly when dnsmasq is run on a separate server.
dnsmasq-2.45-1.1.el5_3 from Red Hat is running.

Virtual machines are started dynamically (using QEMU-KVM) and are
connected to tap0 and tap1 on bridge virbr0. All MAC to IP address
assignments are via /etc/ethers.

sudo brctl show
bridge name	bridge id		STP enabled	interfaces
virbr0		8000.00259010282a	no		tap1
							tap0
							eth1

tcpdump shows the DHCP requests on eth1.

listening on eth1, link-type EN10MB (Ethernet), capture size 96 bytes
05:19:42.338702 IP 0.0.0.0.68 > 255.255.255.255.67: BOOTP/DHCP, Request from 00:50:56:01:00:01, length: 300
05:19:43.150538 IP 0.0.0.0.68 > 255.255.255.255.67: BOOTP/DHCP, Request from 00:50:56:01:01:01, length: 300
05:19:47.149363 IP 0.0.0.0.68 > 255.255.255.255.67: BOOTP/DHCP, Request from 00:50:56:01:01:01, length: 300
05:19:51.150423 IP 0.0.0.0.68 > 255.255.255.255.67: BOOTP/DHCP, Request from 00:50:56:01:01:01, length: 300
05:19:58.152492 IP 0.0.0.0.68 > 255.255.255.255.67: BOOTP/DHCP, Request from 00:50:56:01:01:01, length: 300
05:19:58.336652 IP 0.0.0.0.68 > 255.255.255.255.67: BOOTP/DHCP, Request from 00:50:56:01:00:01, length: 300
05:20:12.189338 IP 0.0.0.0.68 > 255.255.255.255.67: BOOTP/DHCP, Request from 00:50:56:01:01:01, length: 300

The log shows no indication that dnsmasq saw the messages.

Nov 17 05:19:33 allin1 kernel: virbr0: topology change detected, propagating
Nov 17 05:19:33 allin1 kernel: virbr0: port 2(tap0) entering forwarding state
Nov 17 05:19:34 allin1 kernel: virbr0: topology change detected, propagating
Nov 17 05:19:34 allin1 kernel: virbr0: port 3(tap1) entering forwarding state
Nov 17 05:23:02 allin1 dnsmasq[8997]: exiting on receipt of SIGTERM

Extracts from dnsmasq.conf

#interface=eth0
interface=eth1
#interface=eth2
#interface=eth3

no-dhcp-interface=eth0
no-dhcp-interface=eth2

dhcp-range=10.0.0.230,static,255.255.0.0,10m
dhcp-range=10.1.0.230,static,255.255.0.0,10m
dhcp-range=10.2.0.230,static,255.255.0.0,10m
dhcp-range=10.3.0.230,static,255.255.0.0,10m
dhcp-range=10.4.0.230,static,255.255.0.0,10m
dhcp-range=10.5.0.230,static,255.255.0.0,10m
dhcp-range=10.6.0.230,static,255.255.0.0,10m
dhcp-range=10.7.0.230,static,255.255.0.0,10m
dhcp-range=10.8.0.230,static,255.255.0.0,10m
dhcp-range=10.9.0.230,static,255.255.0.0,10m
dhcp-range=10.10.0.230,static,255.255.0.0,10m

cat /etc/ethers
00:50:56:01:00:01 10.0.1.0
00:50:56:01:01:01 10.0.1.1

eth1      Link encap:Ethernet  HWaddr 00:25:90:10:28:2A  
          inet addr:10.0.0.1  Bcast:10.0.255.255  Mask:255.255.0.0
          inet6 addr: fe80::225:90ff:fe10:282a/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:117 errors:0 dropped:0 overruns:0 frame:0
          TX packets:427 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:17430 (17.0 KiB)  TX bytes:76864 (75.0 KiB)
          Memory:d8020000-d8040000 

eth1:101  Link encap:Ethernet  HWaddr 00:25:90:10:28:2A  
          inet addr:10.0.0.101  Bcast:10.0.255.255  Mask:255.255.0.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          Memory:d8020000-d8040000 

tap0      Link encap:Ethernet  HWaddr 06:4E:13:A2:24:EC  
          inet6 addr: fe80::44e:13ff:fea2:24ec/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:10 errors:0 dropped:0 overruns:0 frame:0
          TX packets:6 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:500 
          RX bytes:1836 (1.7 KiB)  TX bytes:1800 (1.7 KiB)

tap1      Link encap:Ethernet  HWaddr 2A:9C:E6:EF:BD:B0  
          inet6 addr: fe80::289c:e6ff:feef:bdb0/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:6 errors:0 dropped:0 overruns:0 frame:0
          TX packets:5 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:500 
          RX bytes:1800 (1.7 KiB)  TX bytes:1186 (1.1 KiB)

virbr0    Link encap:Ethernet  HWaddr 00:25:90:10:28:2A  
          inet addr:10.0.0.101  Bcast:10.0.255.255  Mask:255.255.0.0
          inet6 addr: fe80::225:90ff:fe10:282a/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:453 errors:0 dropped:0 overruns:0 frame:0
          TX packets:18 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:88453 (86.3 KiB)  TX bytes:3737 (3.6 KiB)

sudo netstat -nlp | grep dnsmasq
tcp        0      0 0.0.0.0:53                  0.0.0.0:*                   LISTEN      9254/dnsmasq        
tcp        0      0 :::53                       :::*                        LISTEN      9254/dnsmasq        
udp        0      0 0.0.0.0:53                  0.0.0.0:*                               9254/dnsmasq        
udp        0      0 0.0.0.0:67                  0.0.0.0:*                               9254/dnsmasq        
udp        0      0 :::53                       :::*                                    9254/dnsmasq        

Connection to the LAN is on eth2.

Note, a cross over cable is used between eth0 and eth1 to get the NICs
in "RUNNING" mode. The DHCP request messages did not appear on eth1
until this cable was installed.

Any suggestions will be appreciated.

Eldon





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