BIND and listening on interfaces

Barry Margolin barmar at
Fri Aug 1 15:16:20 UTC 2014

In article <mailman.720.1406904401.26362.bind-users at>,
 Reindl Harald <h.reindl at> wrote:

> the thread yesterday reminded me on my Fedora bugrpeort
> i don't buy "Note that destination IP address must be
> known and set correctly in reply, otherwise clients
> will be confused" because how does it survive NAT

What's meant is that the source address of the reply must match the 
destination address of the request. This is the how TCP behaves 
automatically, since it involves connections, but all UDP packets are 
independent. When BIND sends a reply message, the stack doesn't know 
that it's related to a particular incoming message whose IPs should be 

It survives NAT because the router remembers how it translated the 
incoming packet. When it sees an outgoing packet with the translated IP 
and port, it undoes the translation.

Barry Margolin
Arlington, MA

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