Re: [reSIProcate] DnsResult blacklistLast,greylistLast question.

[Byron Campen <docfaraday@xxxxxxxxx>]

On 12/27/13 3:48 AM, Sergey Pavlov wrote:

On 26 December 2013 06:28, Byron Campen <docfaraday@xxxxxxxxx> wrote:

    So that's the fallback behavior that is specified. In practice, however, sending a bare IP address like that means that UDP will be attempted first, and if that fails for some reason (maybe a NAT is blocking UDP, for example), TCP will be attempted. The specifications are pretty muddy when it comes to transport failover, unfortunately. For sure, if a UA does not support TCP, it should be including a transport param to that effect. Now, as for solving your problem, I see a couple of approaches we could take;

1) Make greylisting configurable (enable/disable).

2) Make handling of sip:<bare-ip-addr> configurable (ie; is this a UDP-only URI, or is TCP a possible second candidate?) This basically boils down to disallowing multiple transport protocols for anything other than an FQDN.

 

Am I understand correctly that in such case UDP transport will not be grey-listed in case of failure a transaction failure? I.e. failed transaction will not influence on other signaling with corresponding IP.

   It would be greylisted if there is a timeout, but because there are no alternatives, it would continue to be used.

 

    Since both of these things are in grey areas of the specifications, both are reasonable things to make configurable. I like the second more, since it is more granular, and I am having a hard time coming up with a reasonable scenario where you'd want to disable greylisting for stuff you got from DNS. Your take?

In our case we will be  satisfied even with second option.  Indeed, greylisting can be really useful for results obtained from DNS lookup. But I think that ability to disable greylisting completely (or according to some predefined list) still should provided. In fact we have two conditions which may cause unanswered requests on UAS side:

1) bug in SIP stack implementation  which is triggered by some specific requests;

2) remote UA  overloaded, completely down or unreachable because of hardware or network malfunction.

Greylisting is good strategy for case (2) but can be real pain for case (1) even with results of real DNS lookups. Just imagine the case when all DNS records points to devices with the same SIP stack implementation  thus all of them can be greylisted by specific SIP request. Since there is no efficient method to distinguish (1) and (2) from UAC point of view it would be good to provide some means to control greylisting strategy for resipprocate stack user.

   I am ok with allowing greylisting to be disabled entirely. It is already a last-ditch measure; if you're observing actual timeouts in the field, things are pretty bad. One thing that might make sense to do is to only greylist after the tuple fails to respond to a stand-alone OPTIONS request (ie; we see a transaction timeout, and then send a quick OPTIONS request to test whether this was a problem specific to the transaction/dialog; if that OPTIONS request times out too, we greylist, or maybe even blacklist).

Best regards,
Byron Campen