This script intended to run as a DHCP server lease script and it manages (registers or removes) static DNS entries in accordance to DHCP lease allocation/expiration.
The script registers only fully qualified domain names (FQDN). Host part of the registering FQDN is the value of the “host-name” property of the lease or the “comment” property if the “host-name” is empty. Domain part is the value of the “domain” property of the corresponding DHCP server network. The script doesn’t register DNS entries for invalid FQDNs with empty or undefined host or domain parts. Also the script doesn’t register DNS entry when the entry with the same IP address or the FQDN already exists in the router’s static DNS database.
Static DNS entries, managed by the script, have the tag #DHCP as a comment to distinguish them from the manually created ones.
The TTL of registering DNS entry is equal to the TTL of the corresponding DHCP lease.
On the DHCP lease expiration the script removes corresponding DNS entry with the same IP address, tagged as #DHCP in the comment.
The script logs various errors and informational messages with the tag DHCP2DNS. The logged messages are self-explanatory.
The script should be created as the standard system script. For the script to run for the given DHCP server, it’s name should be assigned to the “lease-script” property of this server.
Source code follows.
:local DHCPtag
:set DHCPtag "#DHCP"
:if ( [ :len $leaseActIP ] <= 0 ) do={ :error "empty lease address" }
:if ( $leaseBound = 1 ) do=\
{
:local ttl
:local domain
:local hostname
:local fqdn
:local leaseId
:local comment
/ip dhcp-server
:set ttl [ get [ find name=$leaseServerName ] lease-time ]
network
:set domain [ get [ find $leaseActIP in address ] domain ]
.. lease
:set leaseId [ find address=$leaseActIP ]
# Check for multiple active leases for the same IP address. It's weird and it shouldn't be, but just in case.
:if ( [ :len $leaseId ] != 1) do=\
{
:log info "DHCP2DNS: not registering domain name for address $leaseActIP because of multiple active leases for $leaseActIP"
:error "multiple active leases for $leaseActIP"
}
:set hostname [ get $leaseId host-name ]
:set comment [ get $leaseId comment ]
/
:if ( [ :len $hostname ] <= 0 ) do={ :set hostname $comment }
:if ( [ :len $hostname ] <= 0 ) do=\
{
:log error "DHCP2DNS: not registering domain name for address $leaseActIP because of empty lease host-name or comment"
:error "empty lease host-name or comment"
}
:if ( [ :len $domain ] <= 0 ) do=\
{
:log error "DHCP2DNS: not registering domain name for address $leaseActIP because of empty network domain name"
:error "empty network domain name"
}
:set fqdn "$hostname.$domain"
/ip dns static
:if ( [ :len [ find name=$fqdn and address=$leaseActIP and disabled=no ] ] = 0 ) do=\
{
:log info "DHCP2DNS: registering static domain name $fqdn for address $leaseActIP with ttl $ttl"
add address=$leaseActIP name=$fqdn ttl=$ttl comment=$DHCPtag disabled=no
} else=\
{
:log error "DHCP2DNS: not registering domain name $fqdn for address $leaseActIP because of existing active static DNS entry with this name or address"
}
/
} \
else=\
{
/ip dns static
:local dnsDhcpId
:set dnsDhcpId [ find address=$leaseActIP and comment=$DHCPtag ]
:if ( [ :len $dnsDhcpId ] > 0 ) do=\
{
:log info "DHCP2DNS: removing static domain name(s) for address $leaseActIP"
remove $dnsDhcpId
}
/
}
Can someone point me at what I’m doing wrong here? I’ve placed this script in the ‘Lease Script’ section of the DCHP Server setup window. I am watching my leases renew but I am now seeing anything being added to static DNS entries. I also tried adding it as a script and adding /system script run dhcptodns as the Lease Script. I just don’t kinow how this is set up..
Need help. I just moved to MikroTik and this post is exactly what I needed.
After adding the script I can see in the logs the FQDN names are set correctly in the log.
However from the clients, the ping fails with FQDN (ping on just hostname works fine)
Here is my setup - ether4 (10.9.7.0/24) has the script assigned and domain “rev.local”
I have 2 windows machines with static leases
M1 - 10.9.7.11
M2 - 10.9.7.12
Machine are getting correct IP’s, however their DNS server is 9.9.9.9 (which is set on the wan interface)
When I ping from M1
→ ping M2.rev.local → cannot resolve…
→ ping M2 → gets 10.9.7.2 and works fine
Same from M2
However, from the winBox terminal both M1 and M2 work fine with M1.rev.local and M2.rev.local
One more observation. there is M3 which does not have static lease (gets address 10.9.8.131) - can ping to M1, M2 but not M1.rev.local
From what i understand your problem is that the machines (m1, m2 and m3) use 9.9.9.9 as DNS Servers.
They should use the mikrotik as DNS Server. This way they can resolve m1.rev.local and DNS requests for public domains (for example google.com) is forwarded to 9.9.9.9.
I guess that you can even ping m1 or m2 but not .rev.local is coming from the WINS Service. (In this case i guess you are using windows as operating system?)
You can change what DNS Server they are getting in the DHCP section.
I think your DNS is working fine because it worked from winbox.
So the DNS Server set on your client machines is set to 9.9.9.9?
If so, then it just can’t work. Because 9.9.9.9 can’t resolve your internal DNS entries. Only the mikrotik can.
If the DNS is set to 9.9.9.9, and this setting is coming from the DHCP Server, then you have to change what is assigned to them.
I guess your DHCP is also the mikrotik? If so then you have to change the configuration on the DHCP Server in the mikrotik. Since i’m currently not within reach of a mikrotik device i can’t tell you where to go right now. But in the mikrotik wiki should be some helpful article.
So you (at least currently) don’t have to study how DNS works. DHCP is where your problem is in my opinion.
It’s working fine in the long-term version 6.45.8.
You need to put this script in the Lease Script of the DHCP Server, it will be called automatically by new leases.
One thing I did notice is that the script does not run at renew address (after expiration time) but only when the host request a new lease.
Thanks for the script. This should be in the official docs.
I created a slightly modified version:
Strip spaces and \00 chars from DHCP lease host names before combining them with the domain to build DNS fqdn. Some DHCP clients, in my case smart Zyxel switches, register with host names with spaces and trailing \00 chars (this is most likely a Zyxel FW bug)
Generate a hostname for DHCP clients registering with empty host names to create a static DNS A record for all DHCP clients. Most Android devices since Version 8 do not provide host names with DHCP reqs. I like to have working DNS for all clients
Make log prefix configurable
:local DHCPtag "#*# Created by DHCP2DNS #*#"
:local LogPrefix "DHCP2DNS ($leaseServerName)"
###
# Functions
# remove \0 and spaces from string passed as inStr=<string>
:local trimString do=\
{
:local outStr
:for i from=0 to=([:len $inStr] - 1) do=\
{
:local tmp [:pick $inStr $i];
:if (($tmp !=" ") and ($tmp !="\00")) do=\
{
:set outStr ($outStr . $tmp)
}
}
:return $outStr
}
# "a.b.c.d" -> "a-b-c-d" for IP addresses used as replacement for missing host names
:local ip2Host do=\
{
:local outStr
:for i from=0 to=([:len $inStr] - 1) do=\
{
:local tmp [:pick $inStr $i];
:if ($tmp =".") do=\
{
:set tmp "-"
}
:set outStr ($outStr . $tmp)
}
:return $outStr
}
###
# Script entry point
#
# Expected environment variables:
# leaseBound 1 = lease bound, 0 = lease removed
# leaseServerName Name of DHCP server
# leaseActIP IP address of DHCP client
:if ( [ :len $leaseActIP ] <= 0 ) do=\
{
:log error "$LogPrefix: empty lease address"
:error "empty lease address"
}
:if ( $leaseBound = 1 ) do=\
{
# new DHCP lease added
/ip dhcp-server
:local ttl [ get [ find name=$leaseServerName ] lease-time ]
network
:local domain [ get [ find $leaseActIP in address ] domain ]
:set domain [ $trimString inStr=$domain ]
.. lease
:local leaseId [ find address=$leaseActIP ]
# Check for multiple active leases for the same IP address. It's weird and it shouldn't be, but just in case.
:if ( [ :len $leaseId ] != 1) do=\
{
:log warning "$LogPrefix: Multiple active DHCP leases for '$leaseActIP' (???)"
:error "Multiple active DHCP leases for '$leaseActIP' (???)"
}
:local hostname [ get $leaseId host-name ]
:set hostname [ $trimString inStr=$hostname ]
:if ( [ :len $hostname ] <= 0 ) do=\
{
:set hostname [ $ip2Host inStr=$leaseActIP ]
:log info "$LogPrefix: Empty hostname for '$leaseActIP', using generated host name '$hostname'"
}
:if ( [ :len $domain ] <= 0 ) do=\
{
:log warning "$LogPrefix: Empty domainname for '$leaseActIP', cannot create static DNS name"
:error "Empty domainname for '$leaseActIP'"
}
:local fqdn ($hostname . "." . $domain)
/ip dns static
:if ( [ :len [ find name=$fqdn and address=$leaseActIP and disabled=no ] ] = 0 ) do=\
{
add address=$leaseActIP name=$fqdn ttl=$ttl comment=$DHCPtag disabled=no
:log info "$LogPrefix: Static domain name '$fqdn' created for '$leaseActIP' with ttl '$ttl'"
}\
else=\
{
:log warning "$LogPrefix: '$fqdn' already exists, cannot create static DNS name for '$leaseActIP'"
:error "$LogPrefix: '$fqdn' already exists"
}
}\
else=\
{
# DHCP lease removed
/ip dns static
:local dnsDhcpId
:set dnsDhcpId [ find address=$leaseActIP and comment=$DHCPtag ]
:if ( [ :len $dnsDhcpId ] > 0 ) do=\
{
remove $dnsDhcpId
:log info "$LogPrefix: Static DNS name(s) for '$leaseActIP' removed"
}
}
For more flexibility, the above script can be stored in a /system script. This allows to use the same script from all DHCP servers to ease maintenance by putting a small wrapper script into the DHCP server lease script property:
Good script! The only issue I had with it is that it will automatically assume the same lease-time for all (even static) leases, which might not be the case, so I changed