Failure of dhcp server failover

[Eugene Grosbein]

03.05.2016 0:57, Simon Hobson пишет:

> Eugene Grosbein <eugen at grosbein.net> wrote:
>
>> My UniFi APs run with UniFi Controller 3.2.10
>
> That is pretty ancient - there have been a LOT of improvements since (and new firmware for some of the APs).

I known abount new firmware, I use APs compatible with 3.2.10 firmware.

> Unless there's been an update released in the last few days, 4.8.15 is current.

UniFi does not maintain Controller API compatibility between major releases
of the Controller and I cannot just upgrade to 4.x series as I have lots of custom code
utilizing the API. However, I'd like to not discuss this in this list.
  
>> My Cicso router is separating VLANs and relay works per-VLAN. These are just "ip unnumbered" vlans:
>>
>> interface Loopback2
>> description "DHCP default gateway"
>> ip address 31.220.160.2 255.255.255.255
>> no ip redirects
>> !
>> interface Vlan1000
>> description "DHCP Guest"
>> ip unnumbered Loopback2
>> ip helper-address X.X.X.X
>> ip helper-address Y.Y.Y.Y
>> ip verify unicast source reachable-via rx
>
> That is broken.

It works just fine when not in failover mode. Can you provide any references to standards
or DHCP server documentation for restrictions on GI-Addr?

> For DHCP to work properly, you **MUST** have the GI-Addr
>  within the subnet served by the interface on the relay agent -
>  using an un-numbered interface is pretty well guaranteed not to work properly.

"Subnet of the interface" is common notion but an IP network can work without
such notion at all. We use large plain IP pool (like /19) and multiple vlans
routed by set of routers and Router/DHCP relay creates "static" /32 routes
pointing to interface of client on the fly. In such case, interfaces do not have "subnet" notion
but the pool does have its netmask and client has it too. Routers do arp-proxying, of course.

It works just fine when not in failover mode. I can't think a reason
this could work for single ISC DHCP server and not work for a cluster other than bug/race.