[yadifa-users] Questions about 2.2.0's new multi-master feature

Anand Buddhdev anandb at ripe.net
Fri Jul 15 15:11:57 CEST 2016


Dear yadifa developers,

I've just read the documentation about yadifa 2.2.0's new multi-master
feature, something I've been waiting for. However, the documentation is
not clear about what yadifa considers to be failures.

The documentation says "If the preferred name server no longer answers,
the next primary server in the list will be used."

I'd like to ask for details about the "no longer answers" part of that
sentence. As you know, a primary may not answer for a number of reasons,
or may answer with a response other than what yadifa may be expecting.
So here are my questions:

1. Does yadifa first do a query for the SOA record over UDP before it
decides whether a zone transfer is needed, or does it immediately start
a zone transfer over TCP regardless of the current state of the zone?

2. If the SOA query times out (UDP packet loss), or the TCP connection
for IXFR/AXFR times out, is that considered a failure? I assume so.

3. If the TCP connection succeeds, but the primary responds with
SERVFAIL, NOTIMP, NOTAUTH, etc, is that considered a failure or not?

4. If the TCP connection succeeds, and yadifa receives a zone transfer,
but the TSIG digest doesn't match or the clocks are unsynchronised, is
that considered a failure?

5. Is there any reason yadifa always uses the first primary upon notify?
I don't think that's a good design. If a zone has more than one master
listed, then it is reasonable to assume that when a notify comes in,
yadifa should promote that master to the preferred master, and XFR from
it, because it has a newer copy of the zone. Otherwise, yadifa ends up
trying to XFR multiple times, eg:

a) a zone has 2 masters, A and B
b) yadifa gets a NOTIFY from B
c) yadifa tries an XFR from A, but A hasn't updated yet, so no XFR happens
d) yadifa gets a NOTIFY from A, and does the XFR again, and succeeds
this time, but it has wasted one XFR slot in step (c)

It would be nice if the documentation were clear on yadifa's zone
refresh algorithm, as well as explain what precise cases are treated as
failures (or not).

Regards,
Anand


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