We are using the most simple configuration --
We configured one eth port -- set DHCP server.
When the machine is connected to the eth port -- DHCP gives this machine an address.
From the machine, we can ping the mikrotik (192.168.88.1), However, from the Mikrotik, we can not ping that machine by ip address (192.168.88.2xx -- I forget exactly what IP address it was assigned.)

There are no firewalls, nothing in NAT -- we tried to keep the setup as simple as possible

Any ideas why the machine that is connected to the mikrotik, and that received IP address from mikrotik DHCP -- can not ping the mikrotik?

Thanks!

What machine is it? I have expirienced the same issue with notebook running Windows 8. By default, ping is disabled on Windows, it needs to be allowed in windows firewall.

Seeing as you don't remember the IP address you assigned the MikroTik, is it possible you are attempting to ping the wrong IP address? Also, make sure your client computer has a subnet mask capable of "seeing" the MikroTik. (eg 255.255.255.0)

What is the os of the machine? On w7 incoming icmp is blocked by default

its okay, cuz both bootp and dhcp had bigger priority over any other kind of L3 stuff and basically ignore firewall(on well-written firmware with helpers for such)to work, despite absence of separated entries. its basically how networking works.
and as correctly stated - stateful firewall on all Vista and past versions of WIndows - can be configured to block all unsolicited/irrelevant traffic, unless configured otherwise(which is default for most of them, except ATM builds).
so 1st - try configure firewall on PC/node.