Correct Failover / DHCPOFFER functionality
Robert Hille
rch17 at duke.edu
Wed Jul 1 21:41:27 UTC 2009
Thanks for the reply Claus and David,
Actually, Claus is half right about the log. I went back to confirm that
I might have miss-anonymized to log :)
I didn't, both dhcp-07 and dhcp-08 tried to reply via the same IP to
start with. However, the log went on a a bit. Here is the extended, less
anonymized version:
Jun 29 06:08:32 ns-dhcp-07 dhcpd: DHCPDISCOVER from 00:1d:4f:xx:xx:xx
via xx.xx.87.254
Jun 29 06:08:32 ns-dhcp-08 dhcpd: DHCPDISCOVER from 00:1d:4f:xx:xx:xx
via xx.xx.87.253
Jun 29 06:08:33 ns-dhcp-08 dhcpd: DHCPOFFER on 10.144.150.154 to
00:1d:4f:xx:xx:xx (iPod-96) via xx.xx.87.253
Jun 29 06:08:33 ns-dhcp-07 dhcpd: DHCPOFFER on 10.144.150.32 to
00:1d:4f:xx:xx:xx (iPod-96) via xx.xx.87.254
Jun 29 06:08:34 ns-dhcp-07 dhcpd: uid lease 10.144.150.32 for client
00:1d:4f:xx:xx:xx is duplicate on shared-wireless
Jun 29 06:08:34 ns-dhcp-07 dhcpd: uid lease 10.144.150.32 for client
00:1d:4f:xx:xx:xx is duplicate on shared-wireless
Jun 29 06:08:36 ns-dhcp-08 dhcpd: DHCPREQUEST for 10.144.150.154
(10.136.20.4) from 00:1d:4f:xx:xx:xx (iPod-96) via xx.xx.87.253
Jun 29 06:08:36 ns-dhcp-08 dhcpd: DHCPACK on 10.144.150.154 to
00:1d:4f:xx:xx:xx (iPod-96) via xx.xx.87.253
Jun 29 06:08:36 ns-dhcp-07 dhcpd: DHCPREQUEST for 10.144.150.154
(10.136.20.4) from 00:1d:4f:xx:xx:xx via xx.xx.87.253
Jun 29 06:08:36 ns-dhcp-07 dhcpd: DHCPACK on 10.144.150.154 to
00:1d:4f:xx:xx:xx (iPod-96) via xx.xx.87.253
Jun 29 06:08:37 ns-dhcp-08 dhcpd: DHCPREQUEST for 10.144.150.154
(10.136.20.4) from 00:1d:4f:xx:xx:xx (iPod-96) via xx.xx.87.253
Jun 29 06:08:37 ns-dhcp-08 dhcpd: DHCPACK on 10.144.150.154 to
00:1d:4f:xx:xx:xx (iPod-96) via xx.xx.87.253
Jun 29 06:08:37 ns-dhcp-07 dhcpd: DHCPREQUEST for 10.144.150.154
(10.136.20.4) from 00:1d:4f:xx:xx:xx (iPod-96) via xx.xx.87.254
Jun 29 06:08:37 ns-dhcp-07 dhcpd: DHCPACK on 10.144.150.154 to
00:1d:4f:xx:xx:xx (iPod-96) via xx.xx.87.254
Jun 29 06:08:38 ns-dhcp-08 dhcpd: DHCPREQUEST for 10.144.150.154
(10.136.20.4) from 00:1d:4f:xx:xx:xx (iPod-96) via xx.xx.87.254
Jun 29 06:08:38 ns-dhcp-08 dhcpd: DHCPACK on 10.144.150.154 to
00:1d:4f:xx:xx:xx (iPod-96) via xx.xx.87.254
So I get a DISCOVER from both x.x.87.253 and x.x.87.254
So I OFFER an IP to back to both x.x.87.253 and x.x.87.254
There is some uid stuff
dhcp-08 gets a REQUEST from x.x.87.253 and ACKs
dhcp-07 gets a REQUEST from x.x.87.253 and ACK (same IP)
dhcp-08 gets a REQUEST from x.x.87.253 and ACKs (same IP)(again!)
dhcp-07 gets a REQUEST from x.x.87.254 and ACK (same IP)
dhcp-07 gets a REQUEST from x.x.87.254 and ACK (same IP)
So I'm seeing multiple REQUEST/ACKs after the fact.
So what is the normal behavior in failover? Should I see a matched pair
of DISCOVER, OFFER, REPLY, ACK on both severs, or should only the
DISCOVERS be duplicated?
Thanks again,
Rchille
Claus Holm Christensen wrote:
> Robert Hille skrev:
>> The entire DHCPDISCOVER->DHCPOFFER->DCHPREQUEST->DHCPACK is duplicated.
>
> Please note the "via x.x.x.x" extension of the log message. It shows
> that one DISCOVER was forwarded by the .254 router, the other DISCOVER
> by the .253 router. The OFFER is returned to the client through both
> routers.
>
> Since the client don't have an IP address yet, the REQUEST goes out by
> broadcast as well, both routers forward the request and the server
> answer through both routers as well. This isn't exactly correct from
> your logs, but I have a feeling that you may have anonymized the log a
> little and made a small mistake on the last two lines :-)
>
> Later the client will try to renew the lease with unicast REQUEST/ACK
> messages, but this time the exchange shouldn't be duplicated in the logs.
>
>> This doesn't occur on all subnets, and from the reading I'm doing I'm
>> beginning to wonder if it might be network related, maybe something
>> with the helper addresses on the routers?
>
> I think you're right on suspecting the network, I have exactly the same
> pattern in my logs, and this always happend on the VLANs with two
> routers attached, running some sort of failover. I don't remember it on
> the VLANs with only one router alone.
>
>
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