Failover Configuration

[sthaug at nethelp.no]

> > Okay, I assigned them both to port 647 and did a tcpdump. 
> > 
> > It appears as if the primary is successfully contacting the secondary. About
> > once a second I see traffic from the primary going to the secondary. If I
> > tcpdump on the secondary it shows that it's receiving the packet. 
> > 
> > Is this sane? Should the secondary be doing anything? 
> 
> Since this is TCP, the secondary should as a minimum ACK the traffic
> from the primary.
> 
> Here's a quick snapshot of the startup of a failover pair here. Note
> traffic and ACKs going in both directions:

And just to complete the picture - here is some "idle" traffic between
the servers in a failover pair. No DHCP traffic from clients, just the
servers doing their keepalives:

09:40:06.000466 IP primary.519 > secondary.63554: P 39584:39596(12) ack 20200 win 8326 <nop,nop,timestamp 4171200270 126643504>
09:40:06.099723 IP secondary.63554 > primary.519: . ack 39596 win 8326 <nop,nop,timestamp 126661603 4171200270>
09:40:08.000720 IP secondary.63554 > primary.519: P 20200:20212(12) ack 39596 win 8326 <nop,nop,timestamp 126663504 4171200270>
09:40:08.100358 IP primary.519 > secondary.63554: . ack 20212 win 8326 <nop,nop,timestamp 4171202370 126663504>
09:40:26.000940 IP primary.519 > secondary.63554: P 39596:39608(12) ack 20212 win 8326 <nop,nop,timestamp 4171220271 126663504>
09:40:26.100347 IP secondary.63554 > primary.519: . ack 39608 win 8326 <nop,nop,timestamp 126681604 4171220271>
09:40:28.001345 IP secondary.63554 > primary.519: P 20212:20224(12) ack 39608 win 8326 <nop,nop,timestamp 126683505 4171220271>
09:40:28.100816 IP primary.519 > secondary.63554: . ack 20224 win 8326 <nop,nop,timestamp 4171222371 126683505>
09:40:46.000401 IP primary.519 > secondary.63554: P 39608:39620(12) ack 20224 win 8326 <nop,nop,timestamp 4171240271 126683505>
09:40:46.099848 IP secondary.63554 > primary.519: . ack 39620 win 8326 <nop,nop,timestamp 126701604 4171240271>
09:40:48.000968 IP secondary.63554 > primary.519: P 20224:20236(12) ack 39620 win 8326 <nop,nop,timestamp 126703505 4171240271>

Note that there is keepalive traffic (and of course TCP ACK for same)
going in both directions, every 20 seconds.

Steinar Haug, Nethelp consulting, sthaug at nethelp.no