DHCP fail over address delay

[Bryan Dobson]

We had to break the pair to temporarily overcome the issues that it
was causing so some logfiles are not relevant atm unfortunately.

Both servers are running dhcp-3.1.2p1, server1 is FreeBSD and server2
is also FreeBSD but an older version of the OS than on server1.

The servers are in the same subnet in the same data center.

Here's 2 snippets of logs, the first is from a successful transaction,
the second is one where it failed and was a lengthily delay (some IP
details omitted):

WORKED:
server1
Apr  1 10:50:31 server1 dhcpd: DHCPDISCOVER from 00:16:d4:cc:a2:16
(PC) via 10.129.56.1
Apr  1 10:50:31 server1 dhcpd: DHCPOFFER on 65.xxx.42.221 to
00:16:d4:cc:a2:16 (PC) via 10.129.56.1
Apr  1 10:50:31 server1 dhcpd: DHCPREQUEST for 65.xxx.42.221
(216.xxx.192.122) from 00:16:d4:cc:a2:16 (PC) via 10.129.56.1
Apr  1 10:50:31 server1 dhcpd: DHCPACK on 65.xxx.42.221 to
00:16:d4:cc:a2:16 (PC) via 10.129.56.1
Apr  1 10:50:35 server1 dhcpd: DHCPREQUEST for 65.xxx.42.221
(216.xxx.192.122) from 00:16:d4:cc:a2:16 (PC) via 10.129.56.1
Apr  1 10:50:35 server1 dhcpd: DHCPACK on 65.xxx.42.221 to
00:16:d4:cc:a2:16 (PC) via 10.129.56.1
server2
Apr  1 10:50:31 server2 dhcpd: DHCPDISCOVER from 00:16:d4:cc:a2:16
(PC) via 10.129.56.1
Apr  1 10:50:31 server2 dhcpd: DHCPOFFER on 65.xxx.42.221 to
00:16:d4:cc:a2:16 (PC) via 10.129.56.1
Apr  1 10:50:31 server2 dhcpd: DHCPREQUEST for 65.xxx.42.221
(216.xxx.192.122) from 00:16:d4:cc:a2:16 (PC) via 10.129.56.1
Apr  1 10:50:31 server2 dhcpd: DHCPACK on 65.xxx.42.221 to
00:16:d4:cc:a2:16 (PC) via 10.129.56.1
Apr  1 10:50:35 server2 dhcpd: DHCPREQUEST for 65.xxx.42.221
(216.xxx.192.122) from 00:16:d4:cc:a2:16 (PC) via 10.129.56.1
Apr  1 10:50:35 server2 dhcpd: DHCPACK on 65.xxx.42.221 to
00:16:d4:cc:a2:16 (PC) via 10.129.56.1

DID NOT WORK:
server1
Apr  1 10:55:00 server1 dhcpd: DHCPDISCOVER from 00:16:d4:cc:a2:16
(PC) via 10.129.56.1: load balance to peer dhcp
Apr  1 10:55:00 server1 dhcpd: DHCPREQUEST for 65.xxx.42.221
(216.xxx.192.124) from 00:16:d4:cc:a2:16 (PC) via 10.129.56.1
Apr  1 10:55:00 server1 dhcpd: DHCPACK on 65.xxx.42.221 to
00:16:d4:cc:a2:16 (PC) via 10.129.56.1
Apr  1 10:55:05 server1 dhcpd: DHCPREQUEST for 65.xx.42.221
(216.xxx.192.124) from 00:16:d4:cc:a2:16 (PC) via 10.129.56.1
Apr  1 10:55:05 server1 dhcpd: DHCPACK on 65.xxx.42.221 to
00:16:d4:cc:a2:16 (PC) via 10.129.56.1
server2
Apr  1 10:55:00 server2 dhcpd: DHCPDISCOVER from 00:16:d4:cc:a2:16
(PC) via 10.129.56.1
Apr  1 10:55:00 server2 dhcpd: DHCPOFFER on 65.xx.42.221 to
00:16:d4:cc:a2:16 (PC) via 10.129.56.1
Apr  1 10:55:00 server2 dhcpd: DHCPREQUEST for 65.xx.42.221
(216.xxx.192.124) from 00:16:d4:cc:a2:16 (PC) via 10.129.56.1
Apr  1 10:55:00 server2 dhcpd: DHCPACK on 65.xx.42.221 to
00:16:d4:cc:a2:16 (PC) via 10.129.56.1
Apr  1 10:55:05 server2 dhcpd: DHCPREQUEST for 65.xx.42.221
(216.xxx.192.124) from 00:16:d4:cc:a2:16 (PC) via 10.129.56.1
Apr  1 10:55:05 server2 dhcpd: DHCPACK on 65.xx.42.221 to
00:16:d4:cc:a2:16 (PC) via 10.129.56.1

On Thu, Apr 22, 2010 at 4:20 PM, Glenn Satchell
<glenn.satchell at uniq.com.au> wrote:
> That's certainly odd behaviour. However we probably need a little more
> information to help you.
>
> What version of dhcpd are you running (dhcpd --version) ? What Os version,
> and what hardware platform (eg x86, sparc, hp, etc)
>
> Is there anything in the logs? What state does dhcpd start in? Is it
> "normal", "communications-interrupted" or something else? What log messages
> are there on both servers when the request is failed over to server2?
>
> What is the network layout like? Are server1 and server2 on the same subnet,
> in the same data centre or geographically far apart?
>
> regards,
> -glenn
>
> On 04/23/10 08:16, Bryan Dobson wrote:
>>
>> Having a strange issue regarding DHCP fail over which I was wondering
>> anyone else had some across in the past. I have gone over the
>> configuration and believe everything is set as it should be. The issue
>> is we have a pair of DHCP servers set in a fail over configuration and
>> have been seeing excessive delays in IP addresses behind handed out.
>>
>> The servers are running the same version of DHCP and the time on both
>> servers is in sync. If the request comes into server1 and it does not
>> fail over, it will complete the transaction and the user will get an
>> IP. However, if the request is failed over to server2 I have seen a
>> delay of sometimes more than an hour.
>>
>> On server1 we see repeated DHCPDISCOVER to peer until eventually
>> server1 provides the ACK for the address itself.
>>
>> server1 failover:
>>
>> failover peer "dhcp" {
>>   primary;
>>   address server1;
>>   port 51000;
>>   peer address server2;
>>   peer port 51000;
>>   max-response-delay 60;
>>   max-unacked-updates 10;
>>   load balance max seconds 3;
>>   mclt 7200;
>>   split 128;
>> }
>>
>> server2 failover:
>>
>> failover peer "dhcp" {
>>   secondary;
>>   address server2;
>>   port 51000;
>>   peer address server1;
>>   peer port 51000;
>>   max-response-delay 60;
>>   max-unacked-updates 10;
>>   load balance max seconds 3;
>> }
>
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