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Problem with Flat network and DHCP on Mitaka

asked 2016-06-09 12:18:25 -0500

alex123 gravatar image

I've been using OpenStack Juno (RDO, CentOS7) in my lab with Flat network and two compute nodes without any issue.

Today I installed Mitaka (RDO, CentOS7) from the scratch and re-created the same flat network setup. Everything seems to work fine inside the OpenStack (instances get response from the DHCP agent and are able to reach the flat network). However OpenStack DHCP agent (DNSMASQ to be precise) answers DHCPINFORM requests from other PCs connected to the same network (that are NOT OpenStack instances) - driving them crazy - see below DNSMASQ log.

Why is this happening? I'm pretty sure that I didn't have this problem on my Juno setup.
Is there any way to fix this?

[root@openstack-se1 ~(keystone_admin)]# neutron subnet-show public_subnet
+-------------------+--------------------------------------------------+
| Field             | Value                                            |
+-------------------+--------------------------------------------------+
| allocation_pools  | {"start": "10.4.219.224", "end": "10.4.219.244"} |
| cidr              | 10.4.0.0/16                                      |
| created_at        | 2016-06-09T18:01:12                              |
| description       |                                                  |
| dns_nameservers   | 10.1.1.11                                        |
| enable_dhcp       | True                                             |
| gateway_ip        | 10.4.0.1                                         |
| host_routes       |                                                  |
| id                | 74bb197c-8ec0-42d0-b334-e320c50911cc             |
| ip_version        | 4                                                |
| ipv6_address_mode |                                                  |
| ipv6_ra_mode      |                                                  |
| name              | public_subnet                                    |
| network_id        | c70d07a8-35e2-4415-a8bc-249e7d0404a4             |
| subnetpool_id     |                                                  |
| tenant_id         | 4f37f5b23a034e89bb71050deae9eca3                 |
| updated_at        | 2016-06-09T18:01:12                              |
+-------------------+--------------------------------------------------+

tail -f /var/log/neutron/dnsmasq.log

Jun  9 21:01:50 dnsmasq-dhcp[11603]: 575818415 DHCPINFORM(tap0a3d2724-eb) 10.4.2.4 d8:cb:8a:42:a3:5e
Jun  9 21:01:50 dnsmasq-dhcp[11603]: 575818415 tags: tag0, tap0a3d2724-eb
Jun  9 21:01:50 dnsmasq-dhcp[11603]: 575818415 DHCPACK(tap0a3d2724-eb) 10.4.2.4 d8:cb:8a:42:a3:5e IL-ronip-PC
Jun  9 21:01:50 dnsmasq-dhcp[11603]: Ignoring duplicate dhcp-option 26
Jun  9 21:01:50 dnsmasq-dhcp[11603]: 575818415 requested options: 1:netmask, 15:domain-name, 3:router, 6:dns-server,
Jun  9 21:01:50 dnsmasq-dhcp[11603]: 575818415 requested options: 44:netbios-ns, 46:netbios-nodetype, 47:netbios-scope,
Jun  9 21:01:50 dnsmasq-dhcp[11603]: 575818415 requested options: 31:router-discovery, 33:static-route, 121:classless-static-route,
Jun  9 21:01:50 dnsmasq-dhcp[11603]: 575818415 requested options: 249, 43:vendor-encap, 252
Jun  9 21:01:50 dnsmasq-dhcp[11603]: 575818415 next server: 10.4.219.224
Jun  9 21:01:50 dnsmasq-dhcp[11603]: 575818415 sent size:  1 option: 53 message-type  5
Jun  9 21:01:50 dnsmasq-dhcp[11603]: 575818415 sent size:  4 option: 54 server-identifier  10.4.219.224
Jun  9 21:01:50 dnsmasq-dhcp[11603]: 575818415 sent size:  4 option:  1 netmask  255.255.0.0
Jun  9 21:01:50 dnsmasq-dhcp[11603]: 575818415 sent size:  4 option: 28 broadcast  10.4.255.255
Jun  9 21:01:50 dnsmasq-dhcp[11603]: 575818415 sent size: 14 option: 15 domain-name  openstacklocal
Jun  9 21:01:50 dnsmasq-dhcp[11603]: 575818415 sent size:  4 option:  3 router  10.4.0.1
Jun  9 21:01:50 dnsmasq-dhcp[11603]: 575818415 sent size:  4 option:  6 dns-server  10.1.1.11
Jun  9 21:01:50 dnsmasq-dhcp[11603]: 575818415 sent size:  2 option: 26 mtu  1400
Jun  9 21:01:53 dnsmasq-dhcp[11603]: 4293967296 available DHCP subnet: 10.4.0.0/255.255.0.0
Jun  9 21:01:53 dnsmasq-dhcp[11603]: 4293967296 tags: tag0, bootp, tap0a3d2724-eb
Jun  9 21:01:53 dnsmasq-dhcp[11603]: 4293967296 BOOTP ...
(more)
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Comments

We had a similar problem with a provider network (VLAN) to Liberty/RHOSP8. PCs on the physical network used an external DHCP provider, but the combination of the Windows DHCP client using DHCPINFORM and OpenStack dnsmasq "leaking" caused similar symptoms. We fixed it by filtering DHCP in the switch.

Dave Holland gravatar imageDave Holland ( 2017-12-07 02:52:13 -0500 )edit

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answered 2016-06-11 15:24:02 -0500

alex123 gravatar image

The problem was resolved by adding the following to /etc/neutron/dnsmasq-neutron.conf file:

dhcp-ignore=tag:!known

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Asked: 2016-06-09 12:18:25 -0500

Seen: 683 times

Last updated: Jun 11 '16