Deadwood FAQ

INDEX

1. What is Deadwood?
2. How do I use Deadwood?
3. How do I convert a MaraDNS mararc file in to a Deadwood dwood3rc file?
4. I changed a configuration parameter but it has not affected Deadwood
5. Deadwood sends out a lot of queries
6. Steve Gibson's DNS benchmark reports that Deadwood is dropping a lot of DNS packets
7. Can Deadwood blacklist by domain?
8. Does Deadwood have DNSSEC support?
9. Records added to the cache when the timestamp is set to 1970 do not expire
10. I get the error message "Unknown dwood3rc string parameter"

What is Deadwood?

Deadwood is the recursive DNS daemon (service) for MaraDNS 2.0. MaraDNS 2.0 uses separate programs for authoritative records (maradns) and recursive records (Deadwood). Deadwood is a standalone recursive server that can either be used in conjunction with MaraDNS's authoritative server, or by itself. The program can run either in Scientific Linux 6 (and hopefully other Linux and *NIX flavors) or in Windows XP (as well as newer Windows releases).

The reason for this rewrite is because I have never been satisfied with the recursive resolver in MaraDNS 1.0. When I designed MaraDNS 1.0's recursive resolver, there were a number of things needed to get full recursion to work that I did not anticipate. By the time I shoehorned in all of the features needed in a fully recursive DNS server, the code was rather messy and difficult to maintain.

Ever since 2002, my plan has been to rewrite MaraDNS' recursive code. In the fall of 2007, I finally started making the code; the code became MaraDNS' recursive resolver in the fall of 2010.

How do I use Deadwood?

Create a configuration file, /etc/dwood3rc, that looks like this:

bind_address="127.0.0.1"
recursive_acl="127.0.0.1/8"
chroot_dir="/etc/deadwood"

Now, create an empty directory owned by root called /etc/deadwood. Once this is done, compile Deadwood (as per INSTALL.txt), and see if it runs. The above configuration file will only allow connections using the loopback interface on the same machine to resolve domains with Deadwood.

How do I convert a MaraDNS mararc file in to a Deadwood dwood3rc file?

While some effort has been made to have Deadwood use the same syntax and variables as MaraDNS, there are some differences to keep in mind:

Deadwood does not have a "ipv4_alias" parameter.
Deadwood handles "verbose_level" differently; to get fully verbose messages, "verbose_level" has to be 100 (as opposed to MaraDNS' 10)

I changed a configuration parameter but it has not affected Deadwood

Be sure to delete the cache file when making any changes to Deadwood's configuration. In Windows, the cache file is called dw_cache_bin (unless the dwood3rc.txt file is edited); in CentOS, with the default dwood3rc file, the file is called dw_cache.

Deadwood sends out a lot of queries

Deadwood will do this on a slow network, since the default parameters are tuned to get a fast reply on a broadband internet connection. On a slow (dialup, saturated broadband, etc) connection, timeout_seconds should have a value of 7 and num_retries should have a value of 1. This is done by adding the following lines to the dwood3rc file:

timeout_seconds = 7
num_retries = 1

Steve Gibson's DNS benchmark reports that Deadwood is dropping a lot of DNS packets

After running this tool and carefully looking at Deadwood's replies to Gibson's DNS benchmark tool, I can safely conclude that Gibson's tool is buggy and that Deadwood is not dropping the packets being sent to it.

A much better tool to use is Namebench, which correctly shows that Deadwood drops very few (if any) DNS packets sent to it. Namebench is available at available at http://code.google.com/p/namebench/

Can Deadwood blacklist by domain?

Yes.

To blacklist a domain, add a line like this to the dwood3rc file:

upstream_servers["example.com."] = "192.168.255.255"

Replace "example.com." with the domain to be blacklisted, and replace "192.168.255.255" with an IP that is either:

Guaranteed to be unreachable from the server running Deadwood. In this case, any attempt to reach a blacklisted domain will result in Deadwood timing out and eventually returning a "SERVER FAIL" error message.
Running a DNS server that always returns the same IP to a given DNS query. This can be set up by using "csv2_default_zonefile" in MaraDNS, running "microdns" (included in MaraDNS' source tree), or even by running "nanodns".

Deadwood uses a hash to store these blacklisted domains, and should be able to store thousands of such domains without significant slowdown.

If it is more convenient to store the domains in separate files, this can be done using Deadwood's "execfile" mechanism.

Does Deadwood have DNSSEC support?

No. I have nothing against DNSSEC per se, but I plain simply am not in a position to take the time and effort to implement DNSSEC without being compensated for my work.

Records added to the cache when the timestamp is set to 1970 do not expire

Deadwood is year-2038 compliant, even on systems with a 32-bit time_t. In order to pull this off, Deadwood assumes that 32-bit time_t systems showing a timestamp before May 6 2007 (chosen because it was 6 months before the first Deadwood release) have had their clock "wrap around" and that it's really far in the future, not far in the past.

This allows Deadwood to have accurate timestamps on systems with a 32-bit time_t until 2143. The side effect is that Deadwood assumes that systems with a timestamp of 0 are not in 1970, but instead are in the year 2106. This results in all records stored in the cache on systems with an incorrect timestamp not expiring until 2106.

If building Deadwood on a system which sometimes has an incorrect timestamp, there are a couple of ways to work around this:

Run Deadwood on a system with a 64-bit time_t.
Deadwood will interpret a timestamp with a time in 1970 as being in 1970 if time_t is a 64-bit number.
Set up the system to not start up Deadwood unless the system clock is set to May 2007 or later.
Change the value of DW_MINTIME in DwSys.h to a lower or negative value. Note that, if this is set, for example, to -1 instead of its current value (1178488417: May of 2007), Deadwood will start to have inaccurate timestamps on systems with 32-bit time_t in 2106, not 2143. If this is done, please upgrade to a system with a 64-bit time_t before 2106.
Please also note that dwh_put_int64() in DwHash.c (the code that writes the cache to disk) will not correctly store timestamps earlier than March 20, 1979 (they will simply be marked as being on that day). Such records in the cache should immediately expire on systems once the timestamp is correctly set, but this has not been tested at all.

I get the error message "Unknown dwood3rc string parameter"

This error message indicates either one of two things:

The relevant parameter is misspelled. For example, if one has a line like this in their dwood3rc file:
```
bind_adress = "127.0.0.1"
```
This error message will appear. To fix it, correct the spelling of the variable name:
```
bind_address = "127.0.0.1"
```
The relevant parameter is a numeric parameter, but has quotes around it. For example, the following line will trigger this error message:
```
filter_rfc1918 = "0"
```
To correct this, remove the quotes around the number:
```
filter_rfc1918 = 0
```

For the record, all dwood3rc parameters except the following are numeric parameters:

bind_address
cache_file
chroot_dir
ip_blacklist
ipv4_bind_addresses
random_seed_file
recursive_acl
root_servers
upstream_servers