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| -rw-r--r-- | plugin/bind/README.md | 15 |
1 files changed, 11 insertions, 4 deletions
diff --git a/plugin/bind/README.md b/plugin/bind/README.md index 4eeab6c33..a911218f6 100644 --- a/plugin/bind/README.md +++ b/plugin/bind/README.md @@ -84,10 +84,17 @@ You can exclude some addresses by their IP or interface name (The following will ## Bugs -When defining more than one server block, take care not to bind more than one server to the same -address and port. Doing so will result in unpredictable behavior (requests may be randomly -served by either server). Keep in mind that *without* the *bind* plugin, a server will bind to all -interfaces, and this will collide with another server if it's using *bind* to listen to an interface +### Avoiding Listener Contention + +TL;DR, When adding the _bind_ plugin to a server block, it must also be added to all other server blocks that listen on the same port. + +When more than one server block is configured to listen to a common port, those server blocks must either +all use the _bind_ plugin, or all use default binding (no _bind_ plugin). Note that "port" here refers the TCP/UDP port that +a server block is configured to serve (default 53) - not a network interface. For two server blocks listening on the same port, +if one uses the bind plugin and the other does not, two separate listeners will be created that will contend for serving +packets destined to the same address. Doing so will result in unpredictable behavior (requests may be randomly +served by either server). This happens because *without* the *bind* plugin, a server will bind to all +interfaces, and this will collide with another server if it's using *bind* to listen to an address on the same port. For example, the following creates two servers that both listen on 127.0.0.1:53, which would result in unpredictable behavior for queries in `a.bad.example.com`: |