MikroTik RouterBOARD 751U-2HnD User manual

RouterBOARD 751U-2HnD
User's Manual
Copyright and Warranty Information
Copyright and Trademarks. Copyright MikroTikls SIA. This manual
contains information protected by copyright law. No part of it may be
reproduced or transmitted in any form without prior written
permission from the copyright holder. RouterBOARD, RouterOS,
RouterBOOT and MikroTik are trademarks of MikroTikls SIA. All
trademarks and registered trademarks appearing in this manual are
the property of their respective holders.
Hardware. MikroTik warrants all RouterBOARD series equipment for the term of fifteen (15) months from the
shipping date to be free of defects in materials and workmanship under normal use and service, except in case
of damage caused by mechanical, electrical or other accidental or intended damages caused by improper use
or due to wind, rain, fire or other acts of nature.
To return failed units to MikroTik, you must perform the following RMA (Return Merchandise Authorization)
procedure. Follow the instructions below to save time, efforts, avoid costs, and improve the speed of the RMA
process.
1. If you have purchased your product from a MikroTik Reseller, please contact the Reseller company
regarding all warranty and repair issues, the following instructions apply ONLY if you purchased your
equipment directly from MikroTik in Latvia.
2. We do not offer repairs for products that are not covered by warranty. Exceptions can be made for
RB1000, RB1100, RB1200.
3. Out-of-warranty devices and devices not covered by warranty sent to Mikrotikls will be returned to
the sender at sender's cost.
RMA Instructions are located on our webpage here: http://rma.mikrotik.com
Manual. This manual is provided “as is” without a warranty of any kind, expressed or implied, including, but
not limited to, the implied warranty of merchantability and fitness for a particular purpose. The manufacturer
has made every effort to ensure the accuracy of the contents of this manual; however, it is possible that it may
contain technical inaccuracies, typographical or other errors. No liability is assumed for any inaccuracy found
in this publication, nor for direct or indirect, incidental, consequential or other damages that may result from
such an inaccuracy, including, but not limited to, loss of data or profits. Please report any inaccuracies found to
[email protected]om

2
USER'S MANUAL...............................................................................................................................................................1
COPYRIGHT AND WARRANTY INFORMATION...................................................................................................................1
SYSTEM BOARD VIEW AND LAYOUT .................................................................................................................................3
SPECIFICATIONS................................................................................................................................................................3
HARDWARE GUIDE ...........................................................................................................................................................4
MEMORY AND STORAGE DEVICES.................................................................................................................................................4
Memory............................................................................................................................................................................4
Storage Device .................................................................................................................................................................4
INPUT/OUTPUT PORTS...............................................................................................................................................................4
Ethernet ports ..................................................................................................................................................................4
LEDS......................................................................................................................................................................................4
USER'S GUIDE ...................................................................................................................................................................4
POWERING...............................................................................................................................................................................4
BOOTING OPTIONS ....................................................................................................................................................................5
Onboard NAND Storage Device........................................................................................................................................5
Booting from network ......................................................................................................................................................5
Operating System Support ...............................................................................................................................................5
BUTTONS AND JUMPERS .............................................................................................................................................................6
WIRELESS DEVICE ......................................................................................................................................................................6
ROUTERBOOT ...................................................................................................................................................................6
BOOT LOADER CONFIGURATION...................................................................................................................................................6
BOOT LOADER UPGRADING .........................................................................................................................................................6
PRIMARY BOOT LOADER .............................................................................................................................................................6
ROUTEROS FUNCTIONS ....................................................................................................................................................7
FIRMWARE INFORMATION...........................................................................................................................................................7
FIRMWARE SETTINGS .................................................................................................................................................................7
APPENDIX .........................................................................................................................................................................7
CONNECTOR INDEX....................................................................................................................................................................7
BUTTON INDEX .........................................................................................................................................................................8
ETHERNET CABLES .....................................................................................................................................................................8

RouterBOARD 751 Series User's Manual
3
System Board View and Layout
You can download the board dimensions and case design files (PDF and DXF) from www.routerboard.com
Specifications
RouterBOARD 751U-2HnD
CPU
AR7241 400MHz
Memory
32MB DDR SDRAM onboard
Boot loader
RouterBOOT
Data storage
64MB onboard NAND memory chip
Ethernet
Five 10/100 Mbit/s Ethernet ports supporting Auto-MDI/X
MiniPCI slot
-
Expansion
USB 2.0 port
CompactFlash slots
-
Serial port
-
LEDs
Power, NAND activity, 5 Ethernet and 1 wireless LEDs
Beeper
+
Power at the device
DC power jack (5.5mm outside and 2mm inside diameter, female, pin positive plug) accepts 8-30V DC
Power over Ethernet
Ether 1 requires 8-30V DC (non 802.3af), to compensate for losses, it’s recommended to use 12V or more
Power consumption
Up to 7W
Dimensions
113x138x29mm. Weight without packaging and cables: 230g
Temperature
Indoor device. Operational temperature: -20°C to +50°C
Humidity
Operational: up to 70% relative humidity (non-condensing)
RouterOS
RouterOS v5, Level4 license

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Wireless specifications
Wireless
Integrated Wireless 2.4GHz 802.11b/g/n 2x2 MIMO
Antenna
2x2 MIMO PIF antennas, max gain 2.5dBi, external MMCX option
RX Sensitivity
802.11g: -96dBm (6Mbit/s) to -81dBm (54Mbit/s)
802.11n: –96 dBm (MCS0) to –78 dBm (MCS7)
TX Power
802.11g: 30dBm (6Mbps) to 27dBm (54Mbps)
802.11n: 30dBm (MCS0) to 26dBm (MCS7)
Modulations
OFDM: BPSK, QPSK, 16 QAM, 64QAM; DSSS: DBPSK, DQPSK, CCK
Hardware Guide
Memory and Storage Devices
Memory
The RB751U has 32MB of built-in memory. There are no memory upgrade options.
Storage Device
The device is equipped with one 64MB NAND nonvolatile memory chip.
Input/Output Ports
Ethernet ports
There are five individual Ethernet ports. Ports 2-5 are connected to a switch and can be switched together by
an option in the RouterOS software.
All cables made to EIA/TIA 568A/B cable specifications will work correctly (see Connector Index for pinout).
Note that this port supports automatic cross/straight cable correction (Auto MDI/X), so you can use either
straight or cross-over cable for connecting to other network devices.
LEDs
Ethernet LED lights up when a cable is connected, these LEDs don’t show ethernet activity, just connectivity.
Wireless LED flashes on activity. Power LED indicates that the device receives power. ACT LED shows NAND
activity and can be programmed to show other things via RouterOS LED menu.
User's Guide
Powering
The device accepts powering from the power jack or from the first Ethernet port (Passive PoE):
DC power jack (5.5mm outside and 2mm inside diameter, female, pin positive plug) accepts 8-30V DC
The first Ethernet port accepts passive Power over Ethernet accepts 8-30V DC
Under maximum load, the power consumption of this device is 7W

RouterBOARD 751 Series User's Manual
5
Booting options
RouterOS is the operating system of all RouterBOARD routers. Please see detailed configuration guide here
http://wiki.mikrotik.com/wiki/Category:Manual
Initial configuration includes the following:
wirelesss AP with SSID „MikroTik” has been enabled, and bridged to ports Ether2-Ether5. This bridge
has a DHCP server runni ng, so you can connect to the devide using the Web based „Webfig” interface
from Ether2-Ether5 or from the wireless interface. Open http://192.168.88.1 in your browser, in the
page that opens, select „Webfig” and log in with username „admin” and no password. The Ether1 port
has a firewall on it, and a DHCP client, so it’s configured to be connected to your ISP.
An alternative configuration option is the MikroTik Winbox utility (Windows only). Winbox can be used to
connect to the default IP address of 192.168.88.1 with the username admin and no password.
In case you wish to boot the device from network, for example to use MikroTik Netinstall, hold the RESET
button of the device when starting it until the LED light turns off, and the device will start to look for Netinstall
servers. In case IP connection is not available, Winbox can also be used to connect to the MAC address of the
device. More information here: http://wiki.mikrotik.com/wiki/First_time_startup
Onboard NAND Storage Device
The RouterBOARD may be started from the onboard NAND storage chip. As there is no partition table on the
device, the boot loader assumes the first 4MiB form a YAFFS filesystem, and executes the file called “kernel”
stored in the root directory on that partition. It is possible to partition the rest of the medium by patching the
kernel source.
Booting from network
Network boot works similarly to PXE or EtherBoot protocol, and allows you to the device from an executable
image stored on a TFTP server. It uses BOOTP or DHCP (configurable in boot loader) protocol to get a valid IP
address, and TFTP protocol to download an executable (ELF) kernel image combined with the initial RAM disk
(inserted as an ELF section) to boot from (the TFTP server's IP address and the image name must be sent by
the BOOTP/DHCP server).
To boot the RouterBOARD computer from Ethernet network you need the following:
An ELF kernel image for the loader to boot from (you can embed the kernel parameters and initrd image
as ELF sections called kernparm and initrd respectively)
A TFTP server which to download the image from
A BOOTP/DHCP server (may be installed on the same machine as the TFTP server) to give an IP address,
TFTP server address and boot image name
Operating System Support
MikroTik RouterOS starting from version v5 is fully compatible with RouterBOARD 751 series devices. If your
device is preinstalled with an earlier RouterOS release, please upgrade RouterOS to v5.8 or newer.

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Buttons and Jumpers
RouterOS reset jumper hole (on the bottom of case) –resets RouterOS software to defaults. Must
short circuit the metallic sides of the hole with a screwdriver and boot the device. Hold screwdriver in
place until RouterOS configuration is cleared.
RouterBOOT reset button (RES, front panel) has two functions:
oHold this button during boot time until LED light starts flashing, release the button to reset
RouterOS configuration (same result as with RouterOS reset hole)
oHold this button during boot time longer, until LED turns off, then release it to make the
RouterBOARD look for Netinstall servers.
Wireless device
RB751U includes a 2GHz 802.11b/g/n wireless device built in. It has PIF type antennas (2.5dBi) built into the
case, and one MMCX connector for an optional external antenna.
RB 751U has 3 built-in wireless antennas
Chain0
oone antenna for TX
oone antenna for RX
Chain1
oone antenna for TX/RX
oMMCX connector for external antenna
To enable the external MMCX connector, set „antenna mode: antenna-b” in RouterOS wireless settings, in the
HT tab of Winbox. Note: enabling the external antenna disables the built-in Chain1 antenna.
RouterBOOT
The RouterBOOT firmware (also referred as Bootloader here) provides the basic functionality to boot an
Operating System. It supports serial console via the onboard serial port at the boot time. The loader supports
booting from the onboard NAND device and from a network server (see the respective section for details on
this protocol).
Boot Loader Configuration
This device doesn’t come fitted with a serial port connector, so all Bootloader specific settings must be done in
RouterOS. See „RouterOS functions”
Boot Loader Upgrading
The boot loader is needed to initialize all the hardware and boot the system up.
The boot loader upgrading is possible from MikroTik RouterOS, from within the “/system routerboard” menu.
Updates are included with each RouterOS update. The procedure is described in the MikroTik RouterOS
manual: http://wiki.mikrotik.com/wiki/Manual:Bootloader_upgrade
Primary Boot Loader
There are two boot loaders present on the NOR flash memory chip. Secondary is the main one, that is
executed by default. This is the one that can be upgraded. In case something goes wrong in the upgrade
process, or you have set some incorrect settings that render it unusable, you can load the Primary boot loader
by holding the Software Reset 1 button (S401), connecting the power, and then releasing the button/jumper.

RouterBOARD 751 Series User's Manual
7
The Primary boot loader has the default settings, which can not be changed. It is also not possible to upgrade
it.
RouterOS functions
The default OS of RouterBOARD devices is RouterOS, when the routerboard.npk package is installed, RouterOS
can configure some RouterBOARD hardware settings
Firmware information
This menu displays RouterBOARD model number, serial number, the current boot loader version and the
version available in the current software packages installed.
[admin@MikroTik] > system routerboard print
routerboard: yes
model: "rb751u"
serial-number: "154201C1DD3C"
current-firmware: "2.26"
upgrade-firmware: "2.27"
[admin@MikroTik] >
The firmware version can be upgraded from RouterOS by using “/system routerboard upgrade”command.
Firmware Settings
Boot loader settings are also accessible through this menu.
[admin@MikroTik] > system routerboard settings print
boot-delay: 2s
boot-device: nand-if-fail-then-ethernet
boot-protocol: bootp
enable-jumper-reset: yes
[admin@MikroTik] >
Boot-device: use this to enable Netinstall
Boot protocol: for Netinstall use Bootp, for installing other operating systems, you need to use DHCP
Enable-jumper-reset: Disable this to avoid accidental setting reset via the onboard jumper
The Software Reset jumper , which resets both boot loader settings and RouterOS settings by default, can be
disabled in this menu (it will still reset the boot loader settings).
Appendix
Connector Index
Ether1-5
RJ45 Ethernet 100Base-T ports, Ether1 accepts passive PoE power
Power
Power Jack (8-30V DC)
USB
(unlabeled)
USB 2.0 port for connecting 3G modem, storage device or GPS module
ANT
MMCX connector for connecting an external antenna

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Button Index
RES
Software Reset 1 button. (see ”Buttons and Jumpers”)
RESET
(unlabeled)
Software Reset 2 jumper hole. Resets RouterOS settings (see „Buttons and Jumpers”)
Ethernet Cables
RJ45
Pin
Color
Function
(100Mbit)
Function
(1Gbit)
RJ45 pin for Straight cable
(MDI, EIA/TIA568A)
RJ45 pin for Crossover cable
(MDI-X, EIA/TIA568B)
1
Green
TX+ Data
Data A+
1
3
2
Green/White
TX- Data
Data A-
2
6
3
Orange
RX+ Data
Data B+
3
1
4
Blue
-
Data C+
4
4
5
Blue/White
-
Data C-
5
5
6
Orange/White
RX- Data
Data B-
6
2
7
Brown
-
Data D+
7
7
8
Brown/White
-
Data D-
8
8