DHCP IP Assignments

RouterOS General
1

This might qualify as the least important post ever.

I have the following DHCP config:

/ip pool
add comment=offbridge-dhcp-server name=offbridge-dhcp-server ranges=192.168.55.2-192.168.55.200
add name=guest-pool ranges=10.72.2.2-10.72.2.254
add name=iot-pool ranges=10.72.12.2-10.72.12.254
add name=cameras-pool ranges=10.72.22.2-10.72.22.254
add name=mgmt-pool ranges=10.72.32.2-10.72.32.254

/ip dhcp-server
add address-pool=guest-pool interface=vlan-guest 
add address-pool=iot-pool interface=vlan-iot 
add address-pool=cameras-pool interface=vlan-cameras
add address-pool=mgmt-pool interface=vlan-mgmt 
add address-pool=offbridge-dhcp-server 

/ip dhcp-server network
add address=10.72.2.0/24 dns-server=10.72.2.1 gateway=10.72.2.1
add address=10.72.12.0/24 dns-server=10.72.12.1 gateway=10.72.12.1
add address=10.72.22.0/24 dns-server=10.72.22.1 gateway=10.72.22.1
add address=10.72.32.0/24 dns-server=1.1.1.1 gateway=10.72.32.1
add address=192.168.55.0/24 dns-server=1.1.1.1 gateway=192.168.55.1 netmask=24

The DHCP-connected devices are handed out (assigned? leased?) IP address starting from the highest number (.254) in the pool.

Is there a reason why it starts from the highest and not the lowest (.2)?

[admin@729hAPax3] /ip/dhcp-server/lease> print
Flags: D - DYNAMIC
Columns: ADDRESS, MAC-ADDRESS, HOST-NAME, SERVER, STATUS, LAST-SEEN
#   ADDRESS       MAC-ADDRESS        HOST-NAME            SERVER      STATUS  LAST-SEEN
0 D 10.72.12.254  D8:BF:C0:E0:7E:E4  tasmota-E07EE4-7908  dhcp-iot    bound   23m16s   
1 D 10.72.12.253  E8:DB:84:B1:C3:C0  tasmota-B1C3C0-0960  dhcp-iot    bound   16h5m36s 
2 D 10.72.12.252  F4:CF:A2:D9:5A:1E  tasmota-D95A1E-6686  dhcp-iot    bound   4h47s    
3 D 10.72.12.251  48:3F:DA:99:90:86  tasmota-999086-4230  dhcp-iot    bound   3h59m26s 
4 D 10.72.2.254   FA:B5:D0:CE:6D:CF  iPhone               dhcp-guest  bound   1d16h35s 
5 D 10.72.12.250  8E:5C:DA:0C:C7:35  Andres-s-S23-Ultra   dhcp-iot    bound   18h13m58s
2

No, there’s no actual reason. All addresses in DHCP pool are equal.

Server could assign leases randomly … but that would require more CPU resources (choosing a random number, verifying that address is not taken as per DHCP lease table). So DHCP servers go from one address range end towards the other end. And yes, it does seem that going from high end towards low end is more popular.