DNS Client and Cache
|Document revision:||1.3 (November 28, 2007, 10:44 GMT)|
DNS cache is used to minimize DNS requests to an external DNS server as well as to minimize DNS resolution time. This is a simple recursive DNS server with local items.
SpecificationsPackages required: system
License required: Level1
Submenu level: /ip dns
Standards and Technologies: DNS
Hardware usage: Not significant
A MikroTik router with DNS feature enabled can be set as a DNS server for any DNS-compliant client. Moreover, MikroTik router can be specified as a primary DNS server under its dhcp-server settings. When the remote requests are enabled, the MikroTik router responds to TCP and UDP DNS requests on port 53.
DNS Cache SetupSubmenu level: /ip dns
DNS facility is used to provide domain name resolution for router itself as well as for the clients connected to it.
Property Descriptionallow-remote-requests (yes | no; default: no) - specifies whether to allow network requestscache-max-ttl (time; default: 1w) - specifies maximum time-to-live for cache records. In other words, cache records will expire unconditionally after cache-max-ttl time. Shorter TTL received from DNS servers are respectedcache-size (integer: 512..10240; default: 2048KiB) - specifies the size of DNS cache in KiBcache-used (read-only: integer) - displays the current cache size in KiBprimary-dns (IP address; default: 0.0.0.0) - primary DNS serversecondary-dns (IP address; default: 0.0.0.0) - secondary DNS server
If the property use-peer-dns under /ip dhcp-client is set to yes then primary-dns under /ip dns will change to a DNS address given by DHCP Server.
To set 188.8.131.52 as the primary DNS server and allow the router to be used as a DNS server, do the following:
[admin@MikroTik] ip dns> set primary-dns=184.108.40.206 \ \... allow-remote-requests=yes [admin@MikroTik] ip dns> print primary-dns: 220.127.116.11 secondary-dns: 0.0.0.0 allow-remote-requests: yes cache-size: 2048KiB cache-max-ttl: 1w cache-used: 7KiB [admin@MikroTik] ip dns>
Cache MonitoringSubmenu level: /ip dns cache
This menu provides a list with all address (DNS type "A") records stored on the server
Property Descriptionaddress (read-only: IP address) - IP address of the hostname (read-only: name) - DNS name of the hostttl (read-only: time) - remaining time-to-live for the record
All DNS EntriesSubmenu level: /ip dns cache all
This menu provides a complete list with all DNS records stored on the server
Property Descriptiondata (read-only: text) - DNS data field. IP address for type "A" records. Other record types may have different contents of the data field (like hostname or arbitrary text)name (read-only: name) - DNS name of the hostttl (read-only: time) - remaining time-to-live for the recordtype (read-only: text) - DNS record type
Static DNS EntriesSubmenu level: /ip dns static
The MikroTik RouterOS has an embedded DNS server feature in DNS cache. It allows you to link the particular domain names with the respective IP addresses and advertize these links to the DNS clients using the router as their DNS server. This feature can also be used to provide fake DNS information to your network clients. For example, resolving any DNS request for a certain set of domains (or for the whole Internet) to your own page.
The server is capable of resolving DNS requests based on POSIX basic regular expressions, so that multiple requets can be matched with the same entry. In case an entry does not conform with DNS naming standards, it is considered a regular expression and marked with ‘R’ flag. The list is ordered and is checked from top to bottom. Regular expressions are checked first, then the plain records.
Property Descriptionaddress (IP address) - IP address to resolve domain name withname (text) - DNS name to be resolved to a given IP address. May be a regular expressionttl (time) - time-to-live of the DNS record
Reverse DNS lookup (Address to Name) of the regular expression entries is not possible. You can, however, add an additional plain record with the same IP address and specify some name for it.
Remember that the meaning of a dot (.) in regular expressions is any character, so the expression should be escaped properly. For example, if you need to match anything within example.com domain but not all the domains that just end with example.com, like www.another-example.com, use
Regular expression matching is significantly slower than of the plain entries, so it is advised to minimize the number of regular expression rules and optimize the expressions themselves.
To add a static DNS entry for www.example.com to be resolved to 10.0.0.1 IP address:
[admin@MikroTik] ip dns static> add name www.example.com address=10.0.0.1 [admin@MikroTik] ip dns static> print Flags: D - dynamic, X - disabled, R - regexp # NAME ADDRESS TTL 0 www.example.com 10.0.0.1 1d [admin@MikroTik] ip dns static>
Flushing DNS cacheCommand name: /ip dns cache flush
Command Descriptionflush - clears internal DNS cache
[admin@MikroTik] ip dns> cache flush [admin@MikroTik] ip dns> print primary-dns: 18.104.22.168 secondary-dns: 0.0.0.0 allow-remote-requests: yes cache-size: 2048 KiB cache-max-ttl: 1w cache-used: 10 KiB [admin@MikroTik] ip dns>