The LAN & DHCP section covers two things: which address the router itself has on your network, and what it hands out to your devices. It is on by default. The wizard shows two of its fields, the router address and the DHCP switch; advanced mode shows the rest.
This section is about the ordinary, untagged network on the bridge. If you use VLANs, each VLAN gets its own address and its own DHCP server in the VLANs section.
The router's address
The default is 192.168.88.1/24, the MikroTik habit. You enter the address and the prefix together. That address decides two things at once: it is the gateway your devices are given, and if you leave the DHCP pool empty it is derived from this subnet.
With the WAN section switched off you see something different: this device is then a switch or an access point behind an existing router. You choose whether it gets a static address or takes one by DHCP from the existing router. If you choose static, also fill in the gateway, the address of that existing router. Without a gateway, updates, NTP and management from another network do not work, and the configurator warns about it.
Choosing an address range
Nearly every network runs happily on 192.168.88.0/24. Still, there are reasons to pick something else:
- VPN. To dial in from outside, your home network must not use the same range as the network you are dialling in from.
192.168.1.0/24and192.168.0.0/24are in just about every hotel and every relative's house. A range nobody else picks saves trouble later. See Remote access VPN. - Site to site. Linking two locations only works when their subnets differ. See Site to site tunnels.
- Growth. A
/24gives 254 addresses. Plenty for a house, sometimes tight for an office with guest Wi-Fi. Split into VLANs rather than building one large flat network.
Stay inside the private ranges: 10.0.0.0/8, 172.16.0.0 through 172.31.255.255, and 192.168.0.0/16. Note that 172.168.x.x is not private and belongs to somebody else.
Coming from a 192.168.1.1 ISP router
Then you have a choice. Take over the MikroTik range and everything that uses DHCP gets a new address by itself, but devices with a manually set fixed address in the old range are left behind: printers, cameras, a NAS, a thermostat. Those have to be converted one by one, and you can only do that while you can still reach them.
The calm route is to type 192.168.1.1/24 as the router address and keep your old range. Everything keeps working. If you do want to move, make it a separate job, with the list of fixed addresses in front of you, and not on the same evening as replacing the router.
The DHCP server
On by default. The fields that matter:
- DHCP range
- Leave it empty for automatic: the pool then runs from
.10to the last address of the subnet, which keeps the first addresses free for devices that get a fixed one. If you fill it in yourself, the format isstart-end, for example192.168.88.100-192.168.88.200, and the range has to fall inside your subnet; otherwise the field shows an error. - Lease time
- Defaults to
1d. RouterOS notation, so30m,1dor1w. Shorter with a lot of passing guests, longer on a stable network. - DNS server for clients
- The router itself by default. That gives you a cache and one place to filter. Pick custom if you want clients to ask other servers directly, a Pi-hole for instance. See DNS.
- Domain name
- Optional, for example
lan.example.nl. Clients append it to their own name. - NTP server for clients
- Optional. If the router acts as NTP server, fill in the router's address. See System and time.
- Authoritative
- Defaults to
yes. Leave it unless a second DHCP server is supposed to be on the same network.
Fixed addresses
In the fixed addresses table you tie a MAC address to an IP address, with a name so you still know what it was later on. That is nicer than setting a static address on the device itself: the router keeps the list, and the device keeps doing plain DHCP. Pick addresses outside your pool, so below .10 when you use the automatic pool.
ARP entries only for DHCP leases
This switch is off, deliberately. On means the router only talks to devices that hold a lease, and the interface goes to arp=reply-only. That stops devices that invent an address for themselves. It also stops your own devices with a manually set fixed address. Only turn it on when you are sure everything on your network uses DHCP or has a fixed lease.
DHCP relay
Switch the DHCP server off and a DHCP relay option appears: the router passes DHCP requests to a server elsewhere, whose address you fill in. For networks where a Windows server or another central server hands out the addresses.
What ends up in the script
/ip addresswith the router's address on the bridge, or on the management VLAN if you have one./ip poolnameddhcpwith your range./ip dhcp-servernamedgenconf, and/ip dhcp-server networkwith gateway, DNS and domain./ip dhcp-server leaseper fixed address.
On the device you can check it with /ip address print and /ip dhcp-server lease print.
When it does not work
- No address on your laptop. Check that you are in a port that is in the bridge. A port that became WAN hands out no LAN address.
- The subnet is too small. With a prefix that leaves no room for a pool the configurator says so. A
/30has two usable addresses. - Two DHCP servers. If the old ISP router is still connected as a router, two devices hand out addresses and things work one time and not the next.
Read on: VLANs, DNS and Bridge and ports.