[reSIProcate] RRVIP and white list

[Byron Campen]

	Whitelisting is an optional behavior that will cause the stack to  
indefinitely re-use a DNS result that has proven fruitful. So, the  
stack tries to send a message, and gets multiple DNS results. The  
first one that works will be the one that is used from then on,  
regardless of how many DNS results are returned for that same  
hostname in the future. (it will also ignore changes in the  
prioritization built into DNS) This is non-standard behavior, and  
will cause DNS-based load-balancing to not work properly. However,  
there are use-cases for this, which is why it is there.

Best regards,
Byron Campen

> Some  quesitons,
>
> 1) Can anyone explain the rationale behind RRVIP and whitelist?
>
> 2) In DnsInterface, it seems that if we do not define USE_DNS_VIP,  
> then RRVIP and whitelist will not come into play. Then the question  
> comes, why not define USE_DNS_VIP?
>
> 3) What is the reason for the following action?
>
> TransactionState::sendToTU()
> {
> ....
>      // !bwc! Debatable.
>      DnsResult->whitelistLast()
> }
>
> 4) In TransactionState::sendToTU()
>          case 408:
>             if(sipMsg->getReceivedTransport() == 0 && mState ==  
> Trying)  // only blacklist if internally generated and we haven't  
> received any responses yet
>             {
>                // blacklist last target.
>                // ?bwc? How long do we blacklist this for? Probably  
> should make
>                // this configurable. TODO
>                mDnsResult->blacklistLast(resip::Timer::getTimeMs()  
> + 32000);
>             }
>
>             break;
>
> We miss the case where the INVITE client transaction is in Calling  
> state.
>
> BTW, I am referring to 1.1 version.
>
> Thanks,
>
> kaiduan
>
>
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