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plugin/bind: Fix listener collision notes in readme (#5349)

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* clarify listener collision notes in readme

Signed-off-by: Chris O'Haver <cohaver@infoblox.com>

* formatting

Signed-off-by: Chris O'Haver <cohaver@infoblox.com>
This commit is contained in:
Chris O'Haver
2022-04-28 10:06:15 -04:00
committed by GitHub
parent 8c79a30aa9
commit 5a4437bb23
1 changed files with 11 additions and 4 deletions
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15
plugin/bind/README.md
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@@ -84,10 +84,17 @@ You can exclude some addresses by their IP or interface name (The following will
## Bugs ## Bugs
When defining more than one server block, take care not to bind more than one server to the same ### Avoiding Listener Contention
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 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.
interfaces, and this will collide with another server if it's using *bind* to listen to an interface
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, 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`: which would result in unpredictable behavior for queries in `a.bad.example.com`: