[reSIProcate] What does DNS blacklisting mean?

Fri Dec 1 11:38:03 CST 2006

	So, before I took a pickaxe to it, DnsResult::next() would result in  
blacklisting the result it had returned previously. I removed this  
behavior. Now you need to explicitly tell DnsResult that you wish to  
blacklist the last returned tuple. (through DnsResult::blacklistLast 
(), I think) Check out the latest revision. (A note: testDns is very  
different now. It may be hard to digest.)

Best regards,
Byron Campen

> 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
> 	_______________________________________________
> 	resiprocate-devel mailing list
> 	resiprocate-devel at list.resiprocate.org
> 	https://list.resiprocate.org/mailman/listinfo/resiprocate-devel
>
>

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