=== NAME ===

Deadwood - A fully recursive caching DNS resolver 

=== DESCRIPTION ===

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

* Full support for both DNS recursion and DNS forwarding caching

* Small size and memory footprint suitable for embedded systems

* Simple and clean codebase

* Secure design

* Spoof protection: Strong cryptography used to determine the Query ID 
  and source port

* Ability to read and write the cache to a file

* Dynamic cache that deletes entries not recently used

* Ability to use expired entries in the cache when it is impossible to 
  contact upstream DNS servers.

* IPv6 support can be compiled in if desired

* Both DNS-over-UDP and DNS-over-TCP are handled by the same daemon

* Built-in dnswall functionality

* The ability to assign names to IPv4 IPs as specified in one's 
  dwood3rc file.

* The ability to quickly load and use a large blocklist of names to 
  not resolve.

=== 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: 

* Numeric parameters. Numeric parameters must not be surrounded by 
  quotes, such as this example:

filter_rfc1918 = 0

If a numeric parameter is surrounded by quotes, the error message 
"Unknown dwood3rc string parameter" will appear. 

* String parameters. String parameters must be surrounded by quotes, 
  such as in this example:

bind_address = "127.0.0.1"

* Dictionary parameters. All dictionary parameters must be initialized 
  before use, and dictionary parameters must have both the 
  dictionary index and the value for said index surrounded by 
  quotes, such as in this example:

upstream_servers = {} 
upstream_servers["."]="8.8.8.8, 8.8.4.4"

All dwood3rc parameters except the following are numeric parameters: 

* bind_address (string)

* blocked_hosts_hash_file (string)

* cache_file (string)

* chroot_dir (string)

* ip4 (dictionary)

* ip6 (dictionary)

* ip_blacklist (string)

* ip_blocklist (string)

* ipv4_bind_addresses (string)

* random_seed_file (string)

* recursive_acl (string)

* root_servers (dictionary)

* source_ip4 (string)

* upstream_servers (dictionary)

=== 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: 

* 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

* 0.0.x.x

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&nbsp;-f&nbsp;/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. 

=== LEGAL DISCLAIMER ===

THIS SOFTWARE IS PROVIDED BY THE AUTHORS ''AS IS'' AND ANY EXPRESS OR 
IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED 
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE 
DISCLAIMED. IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE FOR 
ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 
DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 
OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 
HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, 
STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING 
IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 
POSSIBILITY OF SUCH DAMAGE. 

=== 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.  


