Domain Name Relay Daemon is a caching, forwarding DNS proxy server. Most useful on vpn or dialup firewalls but it is also a nice DNS cache for minor networks and workstations.
dnrd is a proxying nameserver. DNRD forwards DNS queries to the appropriate nameserver, but can also act as the primary nameserver for a subnet behind a firewall. Proxying is configured on the command line using the -s option. By default, dnrd will act as the primary nameserver for hosts found in /etc/hosts.
Here are some key features of "DNRD":
· Caching of DNS requests.
· Support for backup DNS servers.
· Uses random source port and random query ID's to prevent cache poisoning.
· Support for simple routing - specify different forward DNS servers for different domains.
· Force authorative or unauthorative answers for specified domains.
· Share the /etc/hosts over the network.
· Support for openbsd, freebsd and linux.
· TCP support
· DNS blacklist support
· Sending -SIGHUP will not reread the /etc/hosts file since dnrd is chrooted to /usr/local/etc/dnrd. Use /usr/local/etc/dnrd/master instead and avoid using /etc/hosts at all.
Bind only to the interface with the specified address. By default dnrd binds to everything.
Turn on load balancing. All forward servers that are specified after this option (with -s) will load balance in a round robin scheme. By default, dnrd will use the next server in the list if the first times out. As soon as the first is reactivated, it will be used again. With -b option, dnrd will use next active server as soon a request is served. If a server times out it will be deactivated and will not be used until it comes back. As soon it is reactivated it will join the list.
Note that if there are no -s after the -b, this will do nothing at all.
This option can be used to either turn off caching of DNS responses, or to change the high and low watermarks. With the high/low water mark option, cached entries are purged when the number of responses reaches the high-water mark, and they will be purged until the number of cached responses reaches the low-water mark, purging the oldest first. By default, caching is on, with low and high water-marks of 800 and 1000 respectively.
This turns on debugging level LEVEL. The dnrd process will not fork into the background and print out debugging information in the current console. Supported debug levels are 1-4 The higher level, the more debug info is printed.
The -l option can be used to force dnrd to run in the background and log debug info to syslog.
Sending signal SIGUSR1 will toggle the debug level between level 0 (no debugging) and level 3.
Prints usage information
Ignore cache for deactivated servers. If a forward DNS server times out and gets deactivated, all cache entries for this server are ignored. This helps avoid network timeout delays when dnrd serves a offline/dialup network.
Kills the currently running dnrd process.
Send all messages to syslog. dnrd uses the deamon facility. If used with the -d flag, this option will cause dnrd to fork and run in the background, logging all debugging messages to syslog.
dnrd can act as the primary name server for a number of hosts. By default, it will read in /usr/local/etc/dnrd/master to determine how this is done. If that file doesn't exist, it will act as the primary server for the hosts found in /etc/hosts. This option allows you to override the default behavior. Setting it to off turns off all primary server functionality. Setting it to hosts causes dnrd to act as the primary server for hosts in /etc/hosts regardless of whether it could find /usr/local/etc/dnrd/master.
Sending the signal HUP to the dnrd process will cause the /usr/local/etc/dnrd/master file to be re-read. Since /etc/hosts is outside the chrooted envronment, dnrd will not be able to reread this file. Therefore it is not recommended to use /etc/hosts at all. Future versions of dnrd will not support any use of /etc/hosts.
Set the maximum allowed open sockets. Default is 200.
Set the retry interval time. When a forward DNS server times out it is deactivated. (use the -t option to set the timeout value) dnrd will try to send a request for localhost every N seconds. As soon there are a respose from a deactivated server, it is reactivated. The default value is 10 seconds. Setting this to zero will make dnrd to never deactivate a server.
Add a forward DNS server. If multiple -s options are given, dnrd treats the first as a primary DNS server and the rest as backup servers. If the primary DNS server times out, it is deactivated and the next specified server (that is active) is used until the previous gets reactivated.
The domain option allows dnrd to determine which DNS server should get the query based on the domain name in the query. This is useful when you have an internet connection and a vpn connection to work, for instance. Several servers with the same domain might be specified and then will they work as backup servers.
If -b option is specified, then will all servers specified after the -b option, be grouped by domain, and load balanced.
Set the timeout value for forward DNS servers. If a server don't respond to a query within N seconds it is deactivated. The default value is 20
Setting this to zero will make dnrd to never deactivate a server because of timeouts. However, a server might be deactivated if sendto fails.
By default, dnrd switches to uid 65535 after starting up. This is a security feature. The default uid can be overridden using this option. userid can either be a name or a number.
Prints out the version number.
What's New in This Release:
· Fixes bug that cause all servers for a domain to be disabled upon a timeout.