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:

06:45:15.226201 IP primary.52772 > secondary.519: S 1320673752:1320673752(0) win 65535 <mss 1460,nop,wscale 3,sackOK,timestamp 15306342 0>
06:45:15.227498 IP secondary.519 > primary.52772: S 2660760170:2660760170(0) ack 1320673753 win 65535 <mss 1460,nop,wscale 6,sackOK,timestamp 592369111 15306342>
06:45:15.227525 IP primary.52772 > secondary.519: . ack 1 win 8326 <nop,nop,timestamp 15306344 592369111>
06:45:15.236534 IP primary.52772 > secondary.519: P 1:114(113) ack 1 win 8326 <nop,nop,timestamp 15306353 592369111>
06:45:15.237865 IP secondary.519 > primary.52772: P 1:100(99) ack 114 win 1040 <nop,nop,timestamp 592369121 15306353>
06:45:15.256972 IP primary.52772 > secondary.519: P 114:964(850) ack 100 win 8326 <nop,nop,timestamp 15306373 592369121>
06:45:15.357557 IP secondary.519 > primary.52772: . ack 964 win 1040 <nop,nop,timestamp 592369241 15306373>
06:45:15.363166 IP secondary.519 > primary.52772: P 100:1321(1221) ack 964 win 1040 <nop,nop,timestamp 592369246 15306373>
06:45:15.368789 IP primary.52772 > secondary.519: P 964:1954(990) ack 1321 win 8326 <nop,nop,timestamp 15306485 592369246>
06:45:15.441122 IP secondary.519 > primary.52772: P 1321:2311(990) ack 1954 win 1040 <nop,nop,timestamp 592369324 15306485>
06:45:15.446093 IP primary.52772 > secondary.519: P 1954:2944(990) ack 2311 win 8326 <nop,nop,timestamp 15306562 592369324>
06:45:15.508084 IP secondary.519 > primary.52772: P 2311:3376(1065) ack 2944 win 1040 <nop,nop,timestamp 592369391 15306562>
06:45:15.513277 IP primary.52772 > secondary.519: P 2944:3697(753) ack 3376 win 8326 <nop,nop,timestamp 15306629 592369391>

Steinar Haug, Nethelp consulting, sthaug at nethelp.no