Deadwood - Man Page

A fully recursive caching DNS resolver

 

Description

Deadwood is a fully recursive DNS cache. This is a DNS server with the  following features:  

Command Line Arguments

Deadwood has a single optional command line argument: The location of  the configuration file that Deadwood uses, specified with the "-f"  flag. If this is not defined, Deadwood uses the file "/etc/dwood3rc" as  the configuration file.

In other words, invoking Deadwood as Deadwood will cause Deadwood to use /etc/dwood3rc as the configuration file;  invoking Deadwood as Deadwood -f foobar will cause Deadwood to use the file "foobar" in the current working  directory (the directory one is in when starting Deadwood) as the  configuration file.

Configuration File Format

The Deadwood configuration file is modeled after Python 2's syntax.  However, since Python 2 is no longer supported by the Python Software  Foundation, and since Deadwood configuration files can sometimes fail  to parse in Python 3, Deadwood does not strictly follow Python 2  syntax.

In particular, leading whitespace is allowed in Deadwood configuration  files.

Parameter Types

Deadwood has three different parameter types:  

All dwood3rc parameters except the following are numeric parameters:  

Supported Parameters

The Deadwood configuration file supports the following parameters:

allow_block_hash_zero_key

If this numeric parameter has a value of 1, we allow a blocked hosts  hash file to have a key which is 0. Otherwise, if a blocked hosts file  has a 0 key, Deadwood will terminate when loading the blocked hosts  file with the error message "Zero key block hash not allowed by  default".

There is a security risk if we allow a blocked hosts file to have a 0  key: An attacker with access to a recursive instance of Deadwood could  have Deadwood use more resources than necessary if they know the block  hash file being used. Since the block hash file is read only, hash  flooding attacks are not possible, but an attacker could form queries which use more resources  to resolve as not being present in the block hash.

Deadwood should never be an open recursor and this attack is limited in scope. But be aware  of the risks before setting this parameter to 1.

bind_address

This is the IP (or possibly IPv6) address we bind to.

blocked_hosts_hash_file

A blocked hosts hash file allows Deadwood to block a large number of  host names while using relatively little memory: While using a list of  over 200,000 hosts to block in a dwood3rc file uses over 200 megabytes  of memory, the same list in a block hash file uses only 7 megabytes of  memory.

The block hash file is in a special binary format so that a large  number of host names can be blocked quickly using little memory.

This parameter, if set, is the filename for a block hash file. The file  will be located in the directory set by chroot_dir (usually,  /etc/deadwood). The file name can have lower case letters, the  '-' character (dash), the '_' character (underscore), the  '.' character (dot or period), and the '/' character  (slash). If the file name has the '.' character (dot/period) in  it, it can not have a '/' (slash) after the '.' (dot).

The blockHashMake program generates the block hash file. The contents  of a block hash file can be looked at and read using the blockHashRead  program. See the man pages blockHashMake (1) and blockHashRead (1) for more details.

Block hash files have wildcard support. For example, if "example.com"  is in the block hash file, then deadwood will block "example.com",  "anyname.example.com", "anything.else.example.com",  "12345.example.com", and so on.

Note that wildcards only work for domain names which are one, two, or  three labels long in the database. If "really.bad.example.com" is in  the database, "buzz.really.bad.example.com" will not match, since "really.bad.example.com" has four (i.e. more than three)  labels.

One usable block hash file is available at the repo at  https://github.com/samboy/BlockHash

cache_file

This is the filename of the file used for reading and writing the cache  to disk; this string can have lowercase letters, the '-' symbol,  the '_' symbol, and the '/' symbol (for putting the cache  in a subdirectory). All other symbols become a '_' symbol.

This file is read and written as the user Deadwood runs as.

chroot_dir

This is the directory the program will run from.

deliver_all

This affects behavior in Deadwood 2.3, but has no effect in Deadwood 3.  This variable is only here so Deadwood 2 rc files can run in Deadwood  3.

dns_port

This is the port Deadwood binds to and listens on for incoming  connections. The default value for this is the standard DNS port: port  53

filter_rfc1918

When this has a value of 1, a number of different IP ranges are not  allowed to be in DNS A replies:  

If one of the above IPs is detected in a DNS reply, and filter_rfc1918  has a value of 1, Deadwood will return a synthetic "this host does not  reply" response (a SOA record in the NS section) instead of the A  record.

The reason for this is to provide a "dnswall" that protects users for  some kinds of attacks, as described at http://crypto.stanford.edu/dns/

Please note that Deadwood only provides IPv4 "dnswall" functionality  and does not help protect against IPv6 answers. If protection against  certain IPv6 AAAA records is needed, either disable all AAAA answers by  setting reject_aaaa to have a value of 1, or use an external program to  filter undesired IPv4 answers (such as the dnswall program).

The default value for this is 1

handle_noreply

When this is set to 0, Deadwood sends no reply back to the client (when  the client is a TCP client, Deadwood closes the TCP connection) when a  UDP query is sent upstream and the upstream DNS never sends a reply.

When this is set to 1, Deadwood sends a SERVER FAIL back to the client  when a UDP query is sent upstream and the upstream DNS never sends a  reply.

The default value for this is 1

handle_overload

When this has a value of 0, Deadwood sends no reply when a UDP query is  sent and the server is overloaded (has too many pending connections);  when it has a value of 1, Deadwood sends a SERVER FAIL packet back to  the sender of the UDP query. The default value for this is 1.

hash_magic_number

This used to be used for Deadwood's internal hash generator to keep  the hash generator somewhat random and immune to certain types of  attacks. In Deadwood 3.0, entropy for the hash function is created by  looking at the contents of /dev/urandom (secret.txt on Windows  machines) and the current timestamp. This parameter is only here so  older configuration files do not break in Deadwood 3.0.

ip4

This is a dictionary variable which allows us to have given names  resolve to bogus IPv4 addresses. Here, we have the name "maradns.foo"  resolve to "10.10.10.10" and "kabah.foo" resolve to "10.11.11.11",  regardless of what real values these DNS records may have:

ip4 = {} 
ip4["maradns.foo."] = "10.10.10.10" 
ip4["kabah.foo."] = "10.11.11.11"

Note that a given name can only resolve to a single IP, and that the  records have a fixed TTL of 30 seconds.

It is also possible to use ip4 to set up a blocklist by using "X" for  the IP. When this is done, an IPv4 request for a given hostname results  in a synthetic "this name does not exist" response. In addition, the  corresponding IPv6 request will also return that "name does not exist" reply. For example:

ip4 = {} 
ip4["evil.example.com."] = "X"

Here, both the IPv4 and the IPv6 query for "evil.example.com" will not resolve in Deadwood.

ip6

Like ip4, ip6 uses a similar syntax to have bogus IPv6 addresses. We  don't use standard notation for IPv6 addresses. Instead, we we use  32-character hex addresses (case insensitive); to make it easier to  count long strings of "0"s, the "_" acts like a 0; we also ignore "-"  (dash) and " " (space) in ip6 strings. Here is an example:

ip6 = {} 
ip6["maradns.foo."] = "20010db84d617261444e530000001234" 
ip6["kabah.foo."] = "2001-0DB8-4D61-7261 444E-5300-__00-2345"

ip_blocklist

This is a list of IPs that we do not allow to be in the answer to a DNS  request. The reason for this is to counteract the practice some ISPs  have of converting a "this site does not exist" DNS answer in to a page  controlled by the ISP; this results in possible security issues.

This parameter only accepts individual IPs, and does not use netmasks.

Note that this parameter used to be called ip_blacklist; while the  ip_blacklist name still works as before, ip_blocklist is the current  name.

maradns_uid

The user-id Deadwood runs as. This can be any number between 10 and  16777216; the default value is 707 (a system UID which should be  unused). This value is not used on Windows systems.

maradns_gid

The group-id Deadwood runs as. This can be any number between 10 and  16777216; the default value is 707. This value is not used on Windows  systems.

max_ar_chain

Whether resource record rotation is enabled. If this has a value of 1,  resource record rotation is enabled, otherwise resource record rotation  is disabled.

Resource record rotation is usually desirable, since it allows DNS to  act like a crude load balancer. However, on heavily loaded systems it  may be desirable to disable it to reduce CPU usage.

The reason for the unusual name for this variable is to retain  compatibility with MaraDNS mararc files.

The default value is 1: Resource record rotation enabled.

max_inflights

The maximum number of simultaneous clients we process at the same time  for the same query.

If, while processing a query for, say, "example.com.", another DNS  client sends to Deadwood another query for example.com, instead of  creating a new query to process example.com, Deadwood will attach the  new client to the same query that is already "in flight", and send a  reply to both clients once we have an answer for example.com.

This is the number of simultaneous clients a given query can have. If  this limit is exceeded, subsequents clients with the same query are  refused until an answer is found. If this has a value of 1, we do not  merge multiple requests for the same query, but give each request its  own connection.

The default value is 8.

max_ttl

The maximum amount of time we will keep an entry in the cache, in  seconds (also called "Maximum TTL").

This is the longest we will keep an entry cached. The default value for  this parameter is 86400 (one day); the minimum value is 300 (5 minutes)  and the maximum value this can have is 7776000 (90 days).

The reason why this parameter is here is to protect Deadwood from  attacks which exploit there being stale data in the cache, such as the  "Ghost Domain Names" attack.

maximum_cache_elements

The maximum number of elements our cache is allowed to have. This is a  number between 32 and 16,777,216; the default value for this is 1024.  Note that, if writing the cache to disk or reading the cache from disk,  higher values of this will slow down cache reading/writing.

The amount of memory each cache entry uses is variable depending on the  operating system used and the size of memory allocation pages assigned.  In Windows XP, for example, each entry uses approximately four  kilobytes of memory and Deadwood has an overhead of approximately 512  kilobytes. So, if there are 512 cache elements, Deadwood uses  approximately 2.5 megabytes of memory, and if there are 1024 cache  elements, Deadwood uses approximately 4.5 megabytes of memory. Again,  these numbers are for Windows XP and other operating systems will have  different memory allocation numbers.

Please note that, as of Deadwood 3.5.0004, is is no longer needed to  increase maximum_cache_elements to store upstream_server and  root_server entries.

maxprocs

This is the maximum number of pending remote UDP connections Deadwood  can have. The default value for this is 1024.

max_tcp_procs

This is the number of allowed open TCP connections. Default value: 8

min_ttl

The minimum amount of time we will keep an entry in the cache, in  seconds (also called "Minimum TTL").

num_retries

The number of times we retry to send a query upstream before giving up.  If this is 0, we only try once; if this is 1, we try twice, and so on,  up to 32 retries. Note that each retry takes timeout_seconds seconds  before we retry again. Default value: 5

ns_glueless_type

The RR type we send to resolve glueless records. This should always be  1 (A; i.e. IPv4 DNS servers). This should never be ANY, see RFC8482. This should not be any other value, since only A  glueless NS referrals have ever been tested with Deadwood.

The reason why this exists is because, often times in DNS, we get a  reply like "The name server for this foo.example.com and no I do not  have the IP for foo.example.com" when recursively solving an answer.  So, the question is this: Is foo.example.com an IPv4 DNS server, an  IPv6 server, or both?

On today's internet (mid-2020, during the COVID-19 crisis), the  answer is that the name server in question is only on the IPv4  Internet. IPv6 is now mainstream (e.g. my ISP gives me a /64 and I no  longer have to tunnel through he.net to try out IPv6), but most servers  are still IPv4 only (e.g. my domains are only on IPv4, and amazon.com  does not have an IPv6 address).

The reason this parameter exists is because, when I was writing the  recursive code for Deadwood, I was thinking of a future where IPv6 is  prevalent enough that we would have DNS servers with only IPv6  addresses, and glueless NS referrals (the "foo.example.com" case above)  would point to servers with IPv6, but not IPv4, addresses.

That day may yet come, but preparing Deadwood to still be a viable DNS  server when that day comes will require more than changing the RR type  sent when it gets a glueless NS referral.

random_seed_file

This is a file that contains random numbers, and is used as a seed for  the cryptographically strong random number generator. Deadwood will try  to read 256 bytes from this file (the RNG Deadwood uses can accept a  stream of any arbitrary length).

Note that the hash compression function obtains some of its entropy  before parsing the mararc file, and is hard-coded to get entropy from  /dev/urandom (secret.txt on Windows systems). Most other entropy used  by Deadwood comes from the file pointed to by random_seed_file.

recurse_min_bind_port

The lowest numbered port Deadwood is allowed to bind to; this is a  random port number used for the source port of outgoing queries, and is  not 53 (see dns_port above). This is a number between 1025 and 32767,  and has a default value of 15000. This is used to make DNS spoofing  attacks more difficult.

recurse_number_ports

The number of ports Deadwood binds to for the source port for outgoing  connections; this is a power of 2 between 256 and 32768. This is used  to make DNS spoofing attacks more difficult. The default value is 4096.

recursive_acl

This is a list of who is allowed to use Deadwood to perform DNS  recursion, in "ip/mask" format. Mask must be a number between 0 and 32  (for IPv6, between 0 and 128). For example, "127.0.0.1/8" allows local  connections.

reject_aaaa

If this has a value of 1, a bogus SOA "not there" reply is sent  whenever an AAAA query is sent to Deadwood. In other words, every time  a program asks Deadwood for an IPv6 IP address, instead of trying to  process the request, when this is set to 1, Deadwood pretends the host  name in question does not have an IPv6 address.

This is useful for people who aren't using IPv6 but use applications  (usually *NIX command like applications like "telnet") which slow  things down trying to find an IPv6 address.

This has a default value of 0. In other words, AAAA queries are  processed normally unless this is set.

reject_mx

When this has the default value of 1, MX queries are silently dropped  with their IP logged. A MX query is a query that is only done by a  machine if it wishes to be its own mail server sending mail to machines  on the internet. This is a query an average desktop machine (including  one that uses Outlook or another mail user agent to read and send  email) will never make.

Most likely, if a machine is trying to make a MX query, the machine is  being controlled by a remote source to send out undesired "spam" email.  This in mind, Deadwood will not allow MX queries to be made unless  reject_mx is explicitly set with a value of 0.

Before disabling this, please keep in mind that Deadwood is optimized  to be used for web surfing, not as a DNS server for a mail hub. In  particular, the IPs for MX records are removed from Deadwood's  replies and Deadwood needs to perform additional DNS queries to get the  IPs corresponding to MX records, and Deadwood's testing is more  geared for web surfing (almost 100% A record lookup) and not for mail  delivery (extensive MX record lookup).

reject_ptr

If this has a value of 1, a bogus SOA "not there" reply is sent  whenever a PTR query is sent to Deadwood. In other words, every time a  program asks Deadwood for "reverse DNS lookup" -- the hostname for a  given IP address -- instead of trying to process the request, when this  is set to 1, Deadwood pretends the IP address in question does not have  a hostname.

This is useful for people who are getting slow DNS timeouts when trying  to perform a reverse DNS lookups on IPs.

This has a default value of 0. In other words, PTR queries are  processed normally unless this is set.

resurrections

If this is set to 1, Deadwood will try to send an expired record to the  user before giving up. If it is 0, we don't. Default value: 1

rfc8482

If this is set to 1, Deadwood will not allow ANY or HINFO queries,  sending a RFC8482 response if one is given to Deadwood. If this is 0,  ANY and HINFO queries are allowed. Default value: 1

If ANY queries are enabled, since Deadwood does not support EDNS nor  DNS-over-TCP for upstream queries, Deadwood may not get meaningful  replies from upstream servers.

root_servers

This is a list of root servers; its syntax is identical to  upstream_servers (see below). This is the type of DNS service ICANN,  for example, runs. These are servers used that do not give us complete  answers to DNS questions, but merely tell us which DNS servers to  connect to to get an answer closer to our desired answer.

As of Deadwood 3.5.0004, it is no longer needed to increase  maximum_cache_elements to store root_server entries.

Please be aware that this parameter is deprecated. While there are no  plans to remove this parameter, Deadwood is no longer being updated to  resolve DNS resolution issues when using root_servers to resolve names  on the internet. Please use upstream_servers instead.

source_ip4

With certain complicated networks, it may be desirable to set the  source IP of queries sent to upstream or root DNS servers. If so, set  this parameter to have the dotted decimal IPv4 address to use when  sending IPv4 queries to an upstream DNS server.

Use this parameter with caution; Deadwood can very well become  non-functional if one uses a source IPv4 address which Deadwood is not  bound to.

tcp_listen

In order to enable DNS-over-TCP, this variable must be set and have a  value of 1. Default value: 0

timeout_seconds

This is how long Deadwood will wait before giving up and discarding a  pending UDP DNS reply. The default value for this is 1, as in 1 second,  unless Deadwood was compiled with FALLBACK_TIME enabled.

timeout_seconds_tcp

How long to wait on an idle TCP connection before dropping it. The  default value for this is 4, as in 4 seconds.

ttl_age

Whether TTL aging is enabled; whether entries in the cache have their  TTLs set to be the amount of time the entries have left in the cache.

If this has a value of 1, TTL entries are aged. Otherwise, they are  not. The default value for this is 1.

upstream_port

This is the port Deadwood uses to connect or send packets to the  upstream servers. The default value for this is 53; the standard DNS  port.

upstream_servers

This is a list of DNS servers that the load balancer will try to  contact. This is a dictionary variable (array indexed by a string instead of by a number) instead of a simple  variable. Since upstream_servers is a dictionary variable, it needs to  be initialized before being used.

Deadwood will look at the name of the host that it is trying to find  the upstream server for, and will match against the longest suffix it  can find.

For example, if someone sends a query for "www.foo.example.com" to  Deadwood, Deadwood will first see if there is an upstream_servers  variable for "www.foo.example.com.", then look for "foo.example.com.",  then look for "example.com.", then "com.", and finally ".".

Here is an example of upstream_servers:

upstream_servers = {} # Initialize dictionary variable 
upstream_servers["foo.example.com."] = "192.168.42.1" 
upstream_servers["example.com."] = "192.168.99.254" 
upstream_servers["."] = "10.1.2.3, 10.1.2.4"

In this example, anything ending in "foo.example.com" is resolved by  the DNS server at 192.168.42.1; anything else ending in "example.com"  is resolved by 192.168.99.254; and anything not ending in "example.com"  is resolved by either 10.1.2.3 or 10.1.2.4.

Important: the domain name upstream_servers points to must end in a "." character.  This is OK:

upstream_servers["example.com."] = "192.168.42.1"

But this is not OK:

upstream_servers["example.com"] = "192.168.42.1"

The reason for this is because BIND engages in unexpected behavior when  a host name doesn't end in a dot, and by forcing a dot at the end of  a hostname, Deadwood doesn't have to guess whether the user wants  BIND's behavior or the "normal" behavior.

If neither root_servers nor upstream_servers are set, Deadwood sets  upstream_servers to use the https://quad9.net servers, as follows: 

9.9.9.9 
149.112.112.112

Please note that, as of Deadwood 3.5.0004, is is no longer needed to  increase maximum_cache_elements to store upstream_server entries.

verbose_level

This determines how many messages are logged on standard output; larger  values log more messages. The default value for this is 3.

ip/mask format of IPs

Deadwood uses a standard ip/netmask formats to specify IPs. An ip is in  dotted-decimal format, e.g. "10.1.2.3" (or in IPv6 format when IPv6  support is compiled in).

The netmask is used to specify a range of IPs. The netmask is a single  number between 1 and 32 (128 when IPv6 support is compiled in), which  indicates the number of leading "1" bits in the netmask.

10.1.1.1/24 indicates that any ip from 10.1.1.0 to 10.1.1.255 will match.

10.2.3.4/16 indicates that any ip from 10.2.0.0 to 10.2.255.255 will match.

127.0.0.0/8 indicates that any ip with "127" as the first octet (number) will  match.

The netmask is optional, and, if not present, indicates that only a  single IP will match.

DNS over TCP

DNS-over-TCP needs to be explicitly enabled by setting tcp_listen to 1.

Deadwood extracts useful information from UDP DNS packets marked  truncated which almost always removes the need to have DNS-over-TCP.  However, Deadwood does not cache DNS packets larger than 512 bytes in  size that need to be sent using TCP. In addition, DNS-over-TCP packets  which are "incomplete" DNS replies (replies which a stub resolver can  not use, which can be either a NS referral or an incomplete CNAME  reply) are not handled correctly by Deadwood.

Deadwood has support for both DNS-over-UDP and DNS-over-TCP; the same  daemon listens on both the UDP and TCP DNS port.

Only UDP DNS queries are cached. Deadwood does not support caching over  TCP; it handles TCP to resolve the rare truncated reply without any  useful information or to work with very uncommon non-RFC-compliant  TCP-only DNS resolvers. In the real world, DNS-over-TCP is almost never  used.

Parsing other files

It is possible to have Deadwood, while parsing the dwood3rc file, read  other files and parse them as if they were dwood3rc files.

This is done using execfile. To use execfile, place a line like this in the dwood3rc file:

execfile("path/to/filename")

Where path/to/filename is the path to the file to be parsed like a  dwood3rc file.

All files must be in or under the directory /etc/deadwood/execfile.  Filenames can only have lower-case letters and the underscore character  ("_"). Absolute paths are not allowed as the argument to execfile; the  filename can not start with a slash ("/") character.

If there is a parse error in the file pointed to by execfile, Deadwood  will report the error as being on the line with the execfile command in  the main dwood3rc file. To find where a parse error is in the sub-file,  use something like "Deadwood -f /etc/deadwood/execfile/filename" to  find the parse error in the offending file, where "filename" is the  file to to parsed via execfile.

IPV6 support

This server can also be optionally compiled to have IPv6 support. In  order to enable IPv6 support, add '-DIPV6' to the compile-time  flags. For example, to compile this to make a small binary, and to have  IPv6 support:

	export FLAGS='-Os -DIPV6' 
	make

Security

Deadwood is a program written with security in mind.

In addition to use a buffer-overflow resistant string library and a  coding style and SQA process that checks for buffer overflows and  memory leaks, Deadwood uses a strong pseudo-random number generator  (The 32-bit version of RadioGatun) to generate both the query ID and  source port. For the random number generator to be secure, Deadwood  needs a good source of entropy; by default Deadwood will use  /dev/urandom to get this entropy. If you are on a system without  /dev/urandom support, it is important to make sure that Deadwood has a  good source of entropy so that the query ID and source port are hard to  guess (otherwise it is possible to forge DNS packets).

The Windows port of Deadwood includes a program called  "mkSecretTxt.exe" that creates a 64-byte (512 bit) random file called  "secret.txt" that can be used by Deadwood (via the "random_seed_file"  parameter); Deadwood also gets entropy from the timestamp when Deadwood  is started and Deadwood's process ID number, so it is same to use  the same static secret.txt file as the random_seed_file for multiple  invocations of Deadwood.

Note that Deadwood is not protected from someone on the same network  viewing packets sent by Deadwood and sending forged packets as a reply.

To protect Deadwood from certain possible denial-of-service attacks, it  is best if Deadwood's prime number used for hashing elements in the  cache is a random 31-bit prime number. The program RandomPrime.c  generates a random prime that is placed in the file DwRandPrime.h that  is regenerated whenever either the program is compiled or things are  cleaned up with make clean. This program uses /dev/urandom for its  entropy; the file DwRandPrime.h will not be regenerated on systems  without /dev/urandom.

On systems without direct /dev/urandom support, it is suggested to see  if there is a possible way to give the system a working /dev/urandom.  This way, when Deadwood is compiled, the hash magic number will be  suitably random.

If using a precompiled binary of Deadwood, please ensure that the  system has /dev/urandom support (on Windows system, please ensure that  the file with the name secret.txt is generated by the included  mkSecretTxt.exe program); Deadwood, at runtime, uses /dev/urandom  (secret.txt in Windows) as a hardcoded path to get entropy (along with  the timestamp) for the hash algorithm.

Comments

Deadwood's configuration file format supports two kinds of comments:

# This is a comment

Here, a comment starts with the # character and continues until the end  of the line. In some circumstances, a comment can start after a  variable is set, for example:

bind_address="127.0.0.1" # IP we bind to

The second comment type supports multi-line comments. For example:

_rem={} 
_rem={ #_rem --[=[ 
""" 
 We are now in a multi-line comment. 
 This allows a long explanation to be 
 in a Deadwood configuration file 
""" # ]=] 
}

The actual format is _rem={ at the start of a line, which begins a  multi-line comment. The comment continues until a } is seen. The reason  for this unusual format is that it allows a Deadwood configuration file  to have multi-line comments in a form which are compatible with both  Lua and Python, as can be seen in the above example.

Daemonization

Deadwood does not have any built-in daemonization facilities; this is  handled by the external program Duende or any other daemonizer.

Example configuration file

Here is an example dwood3rc configuration file:

# This is an example deadwood rc file  
# Note that comments are started by the hash symbol 
 
bind_address="127.0.0.1" # IP we bind to 
 
# The following line is disabled by being commented out 
#bind_address="::1" # We have optional IPv6 support 
 
# Directory we run program from (not used in Win32) 
chroot_dir = "/etc/deadwood"  
 
# The following upstream DNS servers are Google's  
# (as of December 2009) public DNS servers.  For  
# more information, see the page at 
# http://code.google.com/speed/public-dns/ 
# 
# If neither root_servers nor upstream_servers are set, 
# Deadwood will use the default ICANN root servers. 
#upstream_servers = {} 
#upstream_servers["."]="8.8.8.8, 8.8.4.4"  
 
# Who is allowed to use the cache.  This line 
# allows anyone with "127.0" as the first two 
# digits of their IP to use Deadwood 
recursive_acl = "127.0.0.1/16"  
 
# Maximum number of pending requests 
maxprocs = 2048 
 
# Send SERVER FAIL when overloaded 
handle_overload = 1  
 
maradns_uid = 99 # UID Deadwood runs as 
maradns_gid = 99 # GID Deadwood runs as 
 
maximum_cache_elements = 60000 
 
# If you want to read and write the cache from disk,  
# make sure chroot_dir above is readable and writable  
# by the maradns_uid/gid above, and uncomment the  
# following line.  
#cache_file = "dw_cache" 
 
# If your upstream DNS server converts "not there" DNS replies 
# in to IPs, this parameter allows Deadwood to convert any reply 
# with a given IP back in to a "not there" IP.  If any of the IPs 
# listed below are in a DNS answer, Deadwood converts the answer 
# in to a "not there" 
#ip_blocklist = "10.222.33.44, 10.222.3.55" 
 
# By default, for security reasons, Deadwood does not allow IPs in  
# the 192.168.x.x, 172.[16-31].x.x, 10.x.x.x, 127.x.x.x,  
# 169.254.x.x, 224.x.x.x, or 0.0.x.x range.  If using Deadwood  
# to resolve names on an internal network, uncomment the  
# following line: 
#filter_rfc1918 = 0

Bugs

Deadwood does not follow RFC2181's advice to ignore DNS responses  with the TC (truncated) bit set, but instead extracts the first RR. If  this is not desired, set the undocumented parameter truncation_hack to  0 (but read the DNS over TCP section of this man page).

Deadwood can not process DNS resource record types with numbers between  65392 and 65407. These RR types are marked by the IANA for "private  use"; Deadwood reserves these record types for internal use. This is  only 16 record types out of the 65536 possible DNS record types (only  71 have actually been assigned by IANA, so this is a non-issue in the  real world).

In addition, Deadwood will, by default, respond to both ANY and HINFO  requests with a RFC8482 compliant packet instead of trying to resolve  the record.

It is not clear whether the DNS RFCs allow ASCII control characters in  DNS names. Even if they were, Deadwood does not allow ASCII control  characters (bytes with a value less then 32) in DNS names. Other  characters (UTF-8, etc.) are allowed.

Combining a CNAME record with other records is prohibited in RFC1034  section 3.6.2 and RFC1912 section 2.4; it makes an answer ambiguous.  Deadwood handles this ambiguity differently than some other DNS  servers.

Authors

Sam Trenholme (http://www.samiam.org) is responsible for this program  and man page. He appreciates all of Jean-Jacques Sarton's help  giving this program IPv6 support.  

Info

August 2009 Deadwood reference