So the problem is that RTO can grows to be twice the failover detection
time. So back to the original mail, the scenario has a switch with failover
detection of 20seconds. Worst case TCP RTO could grow to 40 seconds.
Going back in archive to original mail:
Background
==========
When designing a TCP/IP based network system on failover-capable
network devices, people want to set timeouts hierarchically in
three layers, network device layer, TCP layer, and application
layer (bottom-up order), such that:
1. Network device layer detects a failure first and switch to a
backup device (say, in 20sec).
2. TCP layer timeout & retransmission comes next, _hopefully_
before the application layer timeout.
3. Application layer detects a network failure last (by, say,
30sec timeout) and may trigger a system-level failover.
Sounds like the solution is to make the switch failover detection faster.
If you get switch failover down to 5sec then TCP RTO shouldn't be bigger
than 10sec, and application will survive.
That may indeed be the best solution, we'll have to wait to hear if
there is any freedom there. When this sort of thing has crossed my path
in other contexts, the general answer is that the device failover time
is fixed, and the application layer time is similarly constrained by
end-user expectation/requirement. Often as not, layer 8 and 9 issues
tend to dominate and expect to trump (in this case layer 4 issues).
rick jones
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