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Re: [reSIProcate] DNS not returning entries after 408?

If whitelisting is enabled (which, if I understand correctly, it is not by default), then we will continue using the good server. If we had a greylisting concept, we could afford to greylist for much longer than 32s, but I don't know if it is wise to blacklist for very long in the event of a timeout. (I am sure there are scenarios where this would be desirable behavior, but there are other scenarios where it would not.)

Best regards,
Byron Campen

Good point about the 503’s – I agree.  I am a little worried about only blacklisting a timeout (408) for 32 seconds, when there are alternate servers that could handle requests.  Does this mean that every 32 seconds we will try to send requests to the black listed server again - and fail (assuming the server is down)?  Or will the whitelisting logic kick in and we will continue to use the good server?

 

Scott

 

From: Byron Campen [mailto:docfaraday@xxxxxxx]
Sent: Thursday, December 07, 2006 2:32 PM
To: Scott Godin
Cc: Jeremy Geras; resiprocate-devel@xxxxxxxxxxxxxxxxxxxx
Subject: Re: [reSIProcate] DNS not returning entries after 408?

 

            We can't unblacklist stuff that was blacklisted because of a 503. If all of the available servers are keeling over from overload, and sending 503s, we are supposed to just shut up and wait for the blacklists to expire. However, it is reasonable to say that this behavior is not warranted in cases where we have blacklisted due to a timeout. If we wish to treat these two scenarios differently, maybe a greylisting concept is what we should use.

 

Best regards,

Byron Campen



Before the recent changes, that way I understood it the blacklisting was supposed to work as follows:

1.        Only blacklist an entry if there other DNS entries to try.

2.       If we have ended up blacklisting all entries from a particular lookup, then un-blacklist them all and let the next request start the cycle again.

Scott

 

From: resiprocate-devel-bounces@xxxxxxxxxxxxxxxxxxxx [mailto:resiprocate-devel-bounces@xxxxxxxxxxxxxxxxxxxx] On Behalf Of Byron Campen
Sent: Thursday, December 07, 2006 2:01 PM
To: Jeremy Geras
Cc: resiprocate-devel@xxxxxxxxxxxxxxxxxxxx
Subject: Re: [reSIProcate] DNS not returning entries after 408?

 

          This is happening because the stack is blacklisting the tuple that your server was running on, because it didn't respond. This blacklist (currently) lasts 32s. I was thinking about making this duration configurable. Does anyone want to have a discussion about whether blacklisting on a UDP timeout is something we want to be doing? It seems to me that we might need to have a concept of "greylisting", where greylisted tuples will only be used if they are all that remains to be tried. (This is opposed to a blacklisted tuple, which we should never try, since chances are we have been explicitly told, with a 503, to leave the tuple alone for a while.) Any thoughts? (anyone?)

 

Best regards,

Byron Campen

Hi,

 

I’m using the latest code from SVN (updated today), and I’ve encountered an issue with DNS in the following case:

 

Client                                          Registrar

      REGISTER (due to user login)------------->

      <---------------------------------- 200 OK

 

(at this point the Registrar becomes unavailable – its IP is still reachable, but nothing is listening on UDP port 5060)

 

      re-REGISTER (due to Expires timer)------->

 

(~ 30 seconds go by and then I get a 408 from DUM)

(client sits idle for ~ 30 seconds more)

 

      REGISTER -------------------------------->

 

(Get a 503 Service Unavailable immediately from DUM)

(sit idle for any amount of time)

 

      REGISTER -------------------------------->

      <---------------------------------- 200 OK

 

 

My client is set up to use only UDP as a transport.  I’m using DUM.  I’ve looked at the logs, and it seems the reason I’m getting the 503 is that there aren’t any DNS entries for my registrar: “Ran out of dns entries for 192.168.1.172. Send 503”.  But this doesn’t make sense, as there definitely should be entries (and since I can register if I try once again after I get the 503).

 

If I go back to an older revision (6609 which is from back in September), I don’t have this issue – i.e. I don’t get the 503, my last REGISTER actually goes out on the wire and I get my expected 200 OK.

 

Any thoughts?

 

Thanks,

 - Jeremy -

 

 

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