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Re: [reSIProcate] What does DNS blacklisting mean?

Thanks, that makes sense.  Guess I'm still curious how the DNS layer would
know what happened at the SIP layer.  When I run the 1.0.2 version of
testDns for "sip:yahoo.com", which only has A records, I get a good response
but it appears the A records always get blacklisted:

STACK | 20061130-161358.478 | dcmlaptop | testDns | RESIP:DNS | 21943 | 1026
| DnsResult.cxx:944 | No SRV records for yahoo.com. Trying A records
STACK | 20061130-161358.597 | dcmlaptop | testDns | RESIP:DNS | 21943 | 1026
| dns/DnsStub.cxx:371 | DnsStub::Query::go: yahoo.com type(enum): 1 proto: 1
STACK | 20061130-161358.708 | dcmlaptop | testDns | RESIP:DNS | 21943 | 1026
| DnsResult.cxx:693 | Received dns result for: yahoo.com
STACK | 20061130-161358.708 | dcmlaptop | testDns | RESIP:DNS | 21943 | 1026
| DnsResult.cxx:694 | DnsResult::onDnsResult() 0
STACK | 20061130-161358.708 | dcmlaptop | testDns | RESIP:DNS | 21943 | 1026
| DnsResult.cxx:712 | Adding [ V4 66.94.234.13:5060 UDP target
domain=yahoo.com connectionId=0 ] to result set
STACK | 20061130-161358.708 | dcmlaptop | testDns | RESIP:DNS | 21943 | 1026
| DnsResult.cxx:712 | Adding [ V4 216.109.112.135:5060 UDP target
domain=yahoo.com connectionId=0 ] to result set
DnsHandler received yahoo.com
STACK | 20061130-161358.708 | dcmlaptop | testDns | RESIP:DNS | 21943 | 1026
| DnsResult.cxx:143 | Returning next dns entry: [ V4 66.94.234.13:5060 UDP
target domain=yahoo.com connectionId=0 ]
yahoo.com -> [ V4 66.94.234.13:5060 UDP target domain=yahoo.com
connectionId=0 ]
STACK | 20061130-161358.708 | dcmlaptop | testDns | RESIP:DNS | 21943 | 1026
| DnsResult.cxx:143 | Returning next dns entry: [ V4 216.109.112.135:5060
UDP target domain=yahoo.com connectionId=0 ]
DEBUG | 20061130-161358.709 | dcmlaptop | testDns | RESIP:DNS | 21943 | 1026
| DnsResult.cxx:1197 | Blacklisting yahoo.com(1): 66.94.234.13
DEBUG | 20061130-161358.709 | dcmlaptop | testDns | RESIP:DNS | 21943 | 1026
| DnsResult.cxx:1199 | Remove vip yahoo.com(1)
yahoo.com -> [ V4 216.109.112.135:5060 UDP target domain=yahoo.com
connectionId=0 ]
DEBUG | 20061130-161358.709 | dcmlaptop | testDns | RESIP:DNS | 21943 | 1026
| DnsResult.cxx:1197 | Blacklisting yahoo.com(1): 216.109.112.135
DEBUG | 20061130-161358.709 | dcmlaptop | testDns | RESIP:DNS | 21943 | 1026
| DnsResult.cxx:1199 | Remove vip yahoo.com(1)
STACK | 20061130-161358.709 | dcmlaptop | testDns | RESIP:DNS | 21943 | 1026
| DnsResult.cxx:399 | Priming []
DNS results for sip:yahoo.com
[ V4 66.94.234.13:5060 UDP target domain=yahoo.com connectionId=0 ]
[ V4 216.109.112.135:5060 UDP target domain=yahoo.com connectionId=0 ]
 
Also, if I change testDns to put this in a loop to do a sequence of 4
lookups on the same URI, the ipAddrs always come back in a different order.
Is that caused by blacklisting?  (Call dns.lookup 4 times, wait for all to
complete(), then print results.)  Guess I was thinking that if something was
really "blacklisted" it wouldn't get returned at all on following lookups.

DNS results for sip:yahoo.com
[ V4 216.109.112.135:5060 UDP target domain=yahoo.com connectionId=0 ]
[ V4 66.94.234.13:5060 UDP target domain=yahoo.com connectionId=0 ]
DNS results for sip:yahoo.com
[ V4 66.94.234.13:5060 UDP target domain=yahoo.com connectionId=0 ]
[ V4 216.109.112.135:5060 UDP target domain=yahoo.com connectionId=0 ]
DNS results for sip:yahoo.com
[ V4 216.109.112.135:5060 UDP target domain=yahoo.com connectionId=0 ]
[ V4 66.94.234.13:5060 UDP target domain=yahoo.com connectionId=0 ]
DNS results for sip:yahoo.com
[ V4 66.94.234.13:5060 UDP target domain=yahoo.com connectionId=0 ]
[ V4 216.109.112.135:5060 UDP target domain=yahoo.com connectionId=0 ]

Regards,
Dave

________________________________

From: Byron Campen
Sent: Thursday, November 30, 2006 5:04 PM
To: Dave Mason
Subject: Re: [reSIProcate] What does DNS blacklisting mean?


Ok, in the event that you get a 503 with a Retry-After from a UAS you tried
to send to, you are supposed to refrain from sending to that tuple again
until the Retry-After has expired. The way we do this is allow tuples to be
"blacklisted" for a fixed duration, during which the DNS system will discard
any results pointing to that tuple, as it looks them up. If, however, many
queries were executed simultaneously, it is possible that many DnsResults
will happily give you a blacklisted tuple that they loaded before you
blacklisted it.

Best regards,
Byron Campen


        Hi,

        Hate to ask a noob question, but what does it mean when a DNS query
result
        gets blacklisted?  I saw on the web page it has something to do with
a
        transmit failure, so I assume I shouldn't use the tuples that get
returned
        in the query results vector.  If those results are bad, why do they
still
        get returned?  Is there a status flag I should check before using
them?

        Regards,
        Dave
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