12-27-2013
In a right world, there would be one A record and one PTR for the ip-name pair. For aggressive web hosting, many names resolve to the same IP, either by CNAME or, sadly, additional A records. Is this a need to block web access to all names that go to one IP? An IP block seems more normal. However, for a group of hosts all using the same DNS servers to reach the Internet, you can place CNAME or A records closer to them that will resolve the name to a different address. I once helped a customer set up an AOL proxy on their firewall that way. Everyone behind the firewall thought the firewall host was also some AOL host due to the misplaced A record on the firewall DNS, and the AOL port was a pass through to the real AOL servers.
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LEARN ABOUT DEBIAN
net::dns::async
Net::DNS::Async(3pm) User Contributed Perl Documentation Net::DNS::Async(3pm)
NAME
Net::DNS::Async - Asynchronous DNS helper for high volume applications
SYNOPSIS
use Net::DNS::Async;
my $c = new Net::DNS::Async(QueueSize => 20, Retries => 3);
for (...) {
$c->add(&callback, @query);
}
$c->await();
sub callback {
my $response = shift;
...
}
DESCRIPTION
Net::DNS::Async is a fire-and-forget asynchronous DNS helper. That is, the user application adds DNS questions to the helper, and the
callback will be called at some point in the future without further intervention from the user application. The application need not handle
selects, timeouts, waiting for a response or any other such issues.
If the same query is added to the queue more than once, the module may combine the queries; that is, it will perform the query only once,
and will call each callback registered for that query in turn, passing the same Net::DNS::Response object to each query. For this reason,
you should not modify the Net::DNS::Response object in any way lest you break things horribly for a subsequent callback.
This module is similar in principle to POE::Component::Client::DNS, but does not require POE.
CONSTRUCTOR
The class method new(...) constructs a new helper object. All arguments are optional. The following parameters are recognised as arguments
to new():
QueueSize
The size of the query queue. If this is exceeded, further calls to add() will block until some responses are received or time out.
Retries
The number of times to retry a query before giving up.
Timeout
The timeout for an individual query.
METHODS
$c->add($callback, @query)
Adds a new query for asynchronous handling. The @query arguments are those to Net::DNS::Resolver->bgsend(), q.v. This call will block
if the queue is full. When some pending responses are received or timeout events occur, the call will unblock.
The user callback will be called at some point in the future, with a Net::DNS::Packet object representing the response. If the query
timed out after the specified number of retries, the callback will be called with undef.
$c->await()
Flushes the queue, that is, waits for and handles all remaining responses.
BUGS
The test suite does not test query timeouts.
SEE ALSO
Net::DNS, POE::Component::Client::DNS
COPYRIGHT
Copyright (c) 2005-2006 Shevek. All rights reserved.
This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
perl v5.10.0 2008-10-03 Net::DNS::Async(3pm)