Manual:IP/ARP: Difference between revisions

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{{Versions|3, v4}}
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Revision as of 06:57, 21 October 2009


Applies to RouterOS: 3, v4


Sub-menu: /ip arp

Standards: ARP RFC 826

Even though IP packets are addressed using IP addresses, hardware addresses must be used to actually transport data from one host to another. Address Resolution Protocol is used to map OSI level 3 IP addreses to OSI level 2 MAC addreses. Router has a table of currently used ARP entries. Normally the table is built dynamically, but to increase network security, it can be partialy or completely built statically by means of adding static entries.


Property Description
address (IP; Default: ) IP address to be mapped
interface (name; Default: ) Interface name the IP address is assigned to
mac-address (MAC; Default: 00:00:00:00:00:00) MAC address to be mapped to

Read only properties

Property Description
DHCP (yes | no) True if arp entry is added by DHCP server
dynamic (yes | no) True if entry is dynamically created
invalid (yes | no) True if entry is not valid


Maximal number of ARP entries is 8192.

ARP Modes

It is possible to set several ARP modes in interface configuration .....


If ARP feature is turned off on the interface, i.e., arp=disabled is used, ARP requests from clients are not answered by the router. Therefore, static arp entry should be added to the clients as well. For example, the router's IP and MAC addresses should be added to the Windows workstations using the arp command:

C:\> arp -s  00-aa-00-62-c6-09


This mode is enabled by default on all interfaces. ARPs will be discovered automatically and new dynamic entries will be added to ARP table.

Proxy ARP

A router with properly configured proxy ARP feature acts like a transparent ARP proxy between directly connected networks.
This behaviour can be usefull, for example, if you want to assign dial-in (ppp, pppoe, pptp) clients IP addresses from the same address space as used on the connected LAN.

Reply Only

If arp property is set to reply-only on the interface, then router only replies to ARP requests. Neighbour MAC addresses will be resolved using /ip arp statically, but there will be no need to add the router's MAC address to other hosts' ARP tables like in case if arp is disabled.