maybe a dumb idea on how to fix the dns problems i don't know....

Chris Paul chris.paul at rexconsulting.net
Sun Aug 10 20:27:29 CDT 2008


Joe Greco wrote:
>>> Pretending for a moment that it was even possible to make such large 
>>> scale changes and get them pushed into a large enough number of clients 
>>> to matter, you're talking about meltdown at the recurser level, because
>>> it isn't just one connection per _computer_, but one connection per
>>> _resolver stub_ per _computer_ (which, on a UNIX machine, would tend to
>>> gravitate towards one connection per process), and this just turns into 
>>> an insane number of sockets you have to manage.
>>>       
>>   
>> Couldn't the resolver libraries be changed to not use multiple connections?
>>     
>
> I think that the text I wrote clearly assumes that there IS only one
> connection per resolver instance.  The problem is that hostname to IP
> lookup is pervasive in a modern UNIX system, and is probably pretty
> common on other platforms, too, so you have potentially hundreds or
> thousands of processes, each eating up additional system file descriptors
> for this purpose.

Well how I read what you first wrote implied that the resolvers are now 
going to DOS servers with millions of connections due to each resolver 
stub making a TCP connection...  I say this is something that if true, 
can and should be changed.

Now you say that file descriptors on the client are going to run out 
Isn't that changing the topic? And is that even really a problem?

So each process that needs to do a lookup opens a file descriptor for a 
TCP connection, right? Whereas with UDP we don't have to do this. Is 
this what I'm hearing you say? That I understand. (Hmm don't udp 
connections take sockets too? Not sarcastic here.. just asking...)

And it is a good point but is this client file descriptor an 
insurmountable problem? Also, what about the millions of connections to 
the server? Is that really necessary for a dns resolver on one system to 
open more than one TCP connection to its caching dns server?

I'm not saying that caching dns servers should keep open TCP connections 
to authoritative name servers! OK? But how much latency do you increase 
e on that uncached recursive lookup by changing to TCP?

CP

-- 
Chris Paul
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