DNS problems to RoadRunner - tcp vs udp

Mike Lewinski mike at rockynet.com
Sat Jun 14 19:45:25 CDT 2008


Sean Donelan wrote:

> 1. Separate your authoritative and recursive name servers
> 2. Recursive name servers should only get replies to their own DNS 
> queries from the Internet, they can use both UDP and TCP

We've just completed a project to separate our authoritative and 
recursive servers and I have a couple notes...

1) For the recursive-only, we're using a combination of BIND's 
"query-source address a.b.c.d" and "listen-on e.f.g.h" in the hopes of 
providing some additional measure of protection against cache poisoning. 
The "listen-on" IPs are ACL'd at the borders so non-clients cannot get 
ANY packets to them. The "query-source address" itself doesn't appear in 
the "listen-on" list either and won't respond to queries. I know this 
isn't foolproof, but it probably raises the bar slightly against off-net 
poisoning attempts.

2) The biggest drawback to separation after years of service is that 
customers have come to expect their DNS changes are propagated instantly 
when they are on-net. This turns out to be more of an annoyance to us 
than our customers, since our zone is probably the most frequently updated.

3) I've gone so far as to remove the root hint zone from our auth-only 
boxes, again out of paranoia ("recursion no" does the trick, this is 
just an extra bit of insurance against someone flipping that bit due to 
a lack of understanding of the architecture). There is one third party 
we have to use an 'also-notify' by IP address in this case for their zone.

Mike




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