** Changed in: neutron
Status: Expired => In Progress
** Changed in: neutron
Assignee: (unassigned) => Michael Turek (mjturek)
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https://bugs.launchpad.net/bugs/1500990
Title:
dnsmasq responds with NACKs to requests from unknown hosts
Status in neutron:
In Progress
Bug description:
When a request comes in from a host not managed by neutron, dnsmasq
responds with a NACK. This causes a race condition where if the wrong
DHCP server responds to the request, your request will not be honored.
This can be inconvenient if you are sharing a subnet with other DHCP
servers.
Our team recently ran into this in our Ironic development environment
and were stepping on each other's DHCP requests. A solution is to
provide an option that ignores unknown hosts rather than NACKing them.
The symptom of this was the repeated DISCOVER,OFFER,REQUEST,PACK cycle
with no acceptance from the host. (Sorry for all the omissions, this
may be overly cautious)
Sep 16 09:58:18 localhost dnsmasq-dhcp[30340]: DHCPDISCOVER(tapf1244648-f5)
<MAC address omitted>
Sep 16 09:58:18 localhost dnsmasq-dhcp[30340]: DHCPOFFER(tapf1244648-f5)
<subnet omitted>.205 <MAC address omitted>
Sep 16 09:58:18 localhost dnsmasq-dhcp[30340]: DHCPREQUEST(tapf1244648-f5)
<subnet omitted>.205 <MAC address omitted>
Sep 16 09:58:18 localhost dnsmasq-dhcp[30340]: DHCPACK(tapf1244648-f5)
<subnet omitted>.205 <MAC address omitted> <hostname omitted>
Sep 16 09:58:21 localhost dnsmasq-dhcp[30340]: DHCPDISCOVER(tapf1244648-f5)
<MAC address omitted>
Sep 16 09:58:21 localhost dnsmasq-dhcp[30340]: DHCPOFFER(tapf1244648-f5)
<subnet omitted>.205 <MAC address omitted>
Sep 16 09:58:21 localhost dnsmasq-dhcp[30340]: DHCPREQUEST(tapf1244648-f5)
<subnet omitted>.205 <MAC address omitted>
Sep 16 09:58:21 localhost dnsmasq-dhcp[30340]: DHCPACK(tapf1244648-f5)
<subnet omitted>.205 <MAC address omitted> <hostname omitted>
Sep 16 09:58:25 localhost dnsmasq-dhcp[30340]: DHCPDISCOVER(tapf1244648-f5)
<MAC address omitted>
Sep 16 09:58:25 localhost dnsmasq-dhcp[30340]: DHCPOFFER(tapf1244648-f5)
<subnet omitted>.205 <MAC address omitted>
Sep 16 09:58:25 localhost dnsmasq-dhcp[30340]: DHCPREQUEST(tapf1244648-f5)
<subnet omitted>.205 <MAC address omitted>
Sep 16 09:58:25 localhost dnsmasq-dhcp[30340]: DHCPACK(tapf1244648-f5)
<subnet omitted>.205 <MAC address omitted> <hostname omitted>
...And so on
I did a dhcpdump and saw NACKs coming from my two teammates'
machines.
Of course multiple DHCP servers on a subnet is not a standard or
common case, but we've needed this case in our Ironic development
environment and have found the fix to be useful.
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