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1 UDP Listeners - choosing the right value for -U when starting named

BIND 9.9.0 introduced a new feature to improve performance in multi-threaded environments, particularly those with a large number of processors. The reasons for this are documented here: Performance: Multi-threaded I/O (https://kb.isc.org/article/AA-00629)…

2 Refinements to EDNS fallback behavior can cause different outcomes in Recursive Servers

Recursive DNS Servers administrators have for many years been advised to ensure that both the servers that they are running and the network environments wherein those servers reside are RFC-compliant. This is to ensure the best possible outcome when handling…

3 How do I answer for a specific hostname in a zone, but resolve all its other names normally?

Problem A common wish among many sites with internal-only nameservers is the desire on an otherwise caching-only resolver to override one (or more) single name[s] from the Internet. Suppose your company is "example.com" and your authoritative DNS is hosted…

4 Using the 'map' zone file format in BIND 9.10

What is a zone file format? A zone file is used to store the resource records for a zone. On a master server, the zone file is created externally to BIND, and is usually kept in text format for convenience and flexibility in maintaining it. A master server…

5 How do I enable Response Rate Limiting (RRL) on BIND 9.9.4?

BIND 9.9.4 (and higher) provides support for Response Rate Limiting (RRL). However, it is not enabled by default when building BIND. The reason for this is that BIND 9.9 is an Extended Support Version of BIND and per our policy on mangement of ESVs, we do…

6 Why does my authoritative-only nameserver try to query the root nameservers?

Check first that recursion really is disabled: recursion no; This will prevent your nameserver from performing iterative queries on behalf of any client queries that it receives, but it won't prevent your server from needing to make queries of its own in…

7 Why is my slave server trying sometimes to use a different source IP address for zone transfers?

There are several configuration options in named.conf that control which IPv4 and/or IPv6 source addresses are used for the SOA refresh queries and for the zone transfers themselves. See the Administrator Reference Manual for more details. The well-known…

8 Why does named log an error '3bf305731dd26307.nzf: file not found' when starting up?

When named starts under some configurations it may log a message like: 03-May-2013 18:42:02.807 open: 3bf305731dd26307.nzf: file not found Why does it do that? What is an .nzf file and what happens if named can't find one? Most BIND operators are familiar…

9 When does rndc reconfig flush the cache?

Why does rndc reconfig flush the cache sometimes but not on other occasions? Usually when issuing rndc reconfig to make changes to a running BIND 9 nameserver, you expect it to retain the current working cache of learned RRsets. However, there are a few changes…

10 How do I configure multiple views to share the same recursive cache?

The attach-cache option is used to configure cache-sharing between views. attach-cache cache_name; By default, each view has its own unique cache. When using the attach-cache option, you can specify a name for the cache that named creates for a view. If multiple…