Dag Sonstebo created CLOUDSTACK-9017:
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Summary: VPC VR DHCP broken for multihomed guest VMs
Key: CLOUDSTACK-9017
URL: https://issues.apache.org/jira/browse/CLOUDSTACK-9017
Project: CloudStack
Issue Type: Bug
Security Level: Public (Anyone can view this level - this is the default.)
Components: SystemVM, Virtual Router
Affects Versions: 4.5.2
Environment: CloudStack 4.5.2, XenServer back end.
Reporter: Dag Sonstebo
Priority: Minor
Bug: VPC VR DHCP broken for multihomed guest VMs
Affected version: CloudStack 4.5.2 only tested
Summary: When attaching a guest VM to more than one VPC tier DHCP will only
work for the last NIC to be added. This is according to end user new behaviour
after the CS4.5.2 upgrade.
Workarounds:
1) Only use single NICs on VPC connected VMs and configure L3 routing and ACLs
to handle traffic between tiers.
2) Configure additional tier NICs with the static IP addresses reported by
CloudStack.
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Steps to recreate:
1) Create a VPC with two tiers, in this case
- VPC on 10.3.0.0/16
- Tier 1 on 10.3.1.0/24
- Tier 2 on 10.3.2.0/24
2) Create a new VM attached to tier 1 only. This will cause a new entry to be
written to /etc/dhcphosts.txt on the VPC VR:
root@r-20-VM:~# cat /etc/dhcphosts.txt
02:00:21:fd:00:08,set:10_3_1_162,10.3.1.162,BatVM2,infinite
root@r-20-VM:~#
When the VM starts up the following is displayed in /var/log/dnsmasq.log when
the VM requests it's IP address:
Oct 30 15:50:12 dnsmasq[8246]: read /etc/hosts - 7 addresses
Oct 30 15:50:12 dnsmasq-dhcp[8246]: read /etc/dhcphosts.txt
Oct 30 15:50:12 dnsmasq-dhcp[8246]: read /etc/dhcpopts.txt
Oct 30 15:50:44 dnsmasq-dhcp[8246]: DHCPDISCOVER(eth2) 02:00:21:fd:00:08
Oct 30 15:50:44 dnsmasq-dhcp[8246]: DHCPOFFER(eth2) 10.3.1.162
02:00:21:fd:00:08
Oct 30 15:50:44 dnsmasq-dhcp[8246]: DHCPREQUEST(eth2) 10.3.1.162
02:00:21:fd:00:08
Oct 30 15:50:44 dnsmasq-dhcp[8246]: DHCPACK(eth2) 10.3.1.162 02:00:21:fd:00:08
BatVM2
The following is displayed in the dnsmasq leases file:
root@r-20-VM:~# cat /var/lib/misc/dnsmasq.leases
0 02:00:21:fd:00:08 10.3.1.162 BatVM2 *
And the following in the cloud DHCP configuration file:
root@r-20-VM:~# cat /etc/dnsmasq.d/cloud.conf
dhcp-hostsfile=/etc/dhcphosts.txt
dhcp-range=interface:eth3,set:interface-eth3,10.3.2.1,static
dhcp-option=tag:interface-eth3,15,batvpc.net
dhcp-range=interface:eth2,set:interface-eth2,10.3.1.1,static
dhcp-option=tag:interface-eth2,15,batvpc.net
root@r-20-VM:~#
3) Checking the VM locally IP configuration will show DHCP lease in place for
eth0.
4) Add a new NIC to the VM, attached to Tier 2. This results in the following
entries in the dnsmasq log:
Oct 30 16:23:02 dnsmasq[8246]: read /etc/hosts - 7 addresses
Oct 30 16:23:02 dnsmasq-dhcp[8246]: read /etc/dhcphosts.txt
Oct 30 16:23:02 dnsmasq-dhcp[8246]: read /etc/dhcpopts.txt
Oct 30 16:23:02 dnsmasq-dhcp[8246]: not giving name BatVM2.batvpc.net to the
DHCP lease of 10.3.1.162 because the name exists in /etc/hosts with address
10.3.2.111
Oct 30 16:23:02 dnsmasq-dhcp[8246]: not giving name BatVM2 to the DHCP lease of
10.3.1.162 because the name exists in /etc/hosts with address 10.3.2.111
In other words the Tier 2 address has taken precedence over the initial Tier 1
address.
The /etc/dhcphosts.txt file has now lost the Tier 1 entry and now contains:
root@r-20-VM:~# cat /etc/dhcphosts.txt
02:00:26:94:00:06,set:10_3_2_111,10.3.2.111,BatVM2,infinite
5) When restarting the VM it will fail to get a DHCP lease on eth0.
Note: in some cases it will reuse the old lease which is cached in the local
leases database - note this IP lease does not come from the VPC VR.
The dnsmasq log will now display the following:
Oct 30 16:30:36 dnsmasq-dhcp[8246]: DHCPREQUEST(eth2) 10.3.1.162
02:00:21:fd:00:08
Oct 30 16:30:36 dnsmasq-dhcp[8246]: DHCPNAK(eth2) 10.3.1.162 02:00:21:fd:00:08
address not available
Oct 30 16:30:44 dnsmasq-dhcp[8246]: DHCPDISCOVER(eth2) 02:00:21:fd:00:08 no
address available
Oct 30 16:30:58 dnsmasq-dhcp[8246]: DHCPDISCOVER(eth2) 02:00:21:fd:00:08 no
address available
Oct 30 16:31:13 dnsmasq-dhcp[8246]: DHCPDISCOVER(eth2) 02:00:21:fd:00:08 no
address available
Oct 30 16:31:22 dnsmasq-dhcp[8246]: DHCPDISCOVER(eth2) 02:00:21:fd:00:08 no
address available
Oct 30 16:31:32 dnsmasq-dhcp[8246]: DHCPDISCOVER(eth2) 02:00:21:fd:00:08 no
address available
Oct 30 16:31:37 dnsmasq-dhcp[8246]: DHCPDISCOVER(eth3) 02:00:26:94:00:06
Oct 30 16:31:37 dnsmasq-dhcp[8246]: DHCPOFFER(eth3) 10.3.2.111
02:00:26:94:00:06
Oct 30 16:31:37 dnsmasq-dhcp[8246]: DHCPREQUEST(eth3) 10.3.2.111
02:00:26:94:00:06
Oct 30 16:31:37 dnsmasq-dhcp[8246]: DHCPACK(eth3) 10.3.2.111 02:00:26:94:00:06
BatVM2
I.e. the VM is not receiving a DHCP offer on eth0 as there are no addresses
configured, however eth1 successfully handshakes.
6) Note - restart of the VPC VR / restart of network with cleanup does not seem
to fix the issue.
7) Just removing the last added NIC does not fix the issue:
The DHCP host file still contains the following, i.e. the host entry from the
last added NIC:
root@r-20-VM:~# cat /etc/dhcphosts.txt
02:00:26:94:00:06,set:10_3_2_111,10.3.2.111,BatVM2,infinite
root@r-20-VM:~#
Restarting the VM after removal will show:
Oct 30 16:42:00 dnsmasq-dhcp[8246]: DHCPREQUEST(eth2) 10.3.1.162
02:00:21:fd:00:08
Oct 30 16:42:00 dnsmasq-dhcp[8246]: DHCPNAK(eth2) 10.3.1.162 02:00:21:fd:00:08
address not available
Oct 30 16:42:08 dnsmasq-dhcp[8246]: DHCPDISCOVER(eth2) 02:00:21:fd:00:08 no
address available
Oct 30 16:42:19 dnsmasq-dhcp[8246]: DHCPDISCOVER(eth2) 02:00:21:fd:00:08 no
address available
Oct 30 16:42:30 dnsmasq-dhcp[8246]: DHCPDISCOVER(eth2) 02:00:21:fd:00:08 no
address available
Oct 30 16:42:50 dnsmasq-dhcp[8246]: DHCPDISCOVER(eth2) 02:00:21:fd:00:08 no
address available
I.e. still no DHCP lease on Tier 1.
8) Getting DHCP to work again on the guest VM eth0 involves juggling NICs:
- Making the last added NIC (eth1) primary.
- Remove the first NIC (eth0) as discussed in step 7 above.
- Readding a new NIC on Tier1.
- At this point DHCP will work on the Tier 1 NIC, but will be broken on
the Tier 2 NIC.
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