Overview

IP addresses serve for a general host identification purposes in IP networks (RFC 791). Typical (IPv4) address consists of four octets. For proper addressing the router also needs the network mask value, id est which bits of the complete IP address refer to the address of the host, and which - to the address of the network. The network address value is calculated by binary AND operation from network mask and IP address values. It's also possible to specify IP address followed by slash "/" and the amount of bits that form the network address.

In most cases, it is enough to specify the address, the netmask, and the interface arguments. The network prefix and the broadcast address are calculated automatically.

It is possible to add multiple IP addresses to an interface or to leave the interface without any addresses assigned to it. In case of bridging or PPPoE connection, the physical interface may not have any address assigned, yet be perfectly usable. Configuring an IP address to a physical interface included in a bridge would mean actually setting it on the bridge interface itself. You can use /ip address print detail to see which interface the address belongs to.

IPv4 Addressing

IPv4 uses 4 byte addresses which is segmented in four 8-bit fileds called octets. Each octet is converted to decimal format and separated by dot. For example:

11000000 10101000 00000011 00011000 => 192.168.3.24

IPv4 network consists of three addresses:

network address - a standard way to refer to an IPv4 address assigned to a network. For example, we could refer to the network 192.168.1.0 or 172.16.0.0 as a “Network Address.”
broadcast address - a special address for each network that allows communication to all the hosts in that network. The broadcast address uses the highest address in the network range. for example, broadcast address if 192.168.1.0/24 network will be 192.168.1.255
host address - any other address that is not network address and broadcast address can be used as host address. For example, 192.168.1.2 - 254 host addresses can be used from 192.168.1.0/24 address range

There are several types of IP addressing

unicast - normally refers to a single sender or a single receiver, and can be used for both sending and receiving. Usually, a unicast address is associated with a single device or host, but it is not a one-to-one correspondence.
broadcast - address to send data to all possible destinations ("all-hosts broadcast"), which permits the sender to send the data only once, and all receivers receive a copy of it. In the IPv4 protocol, the address 255.255.255.255 is used for local broadcast. In addition, a directed (limited) broadcast can be made by combining the network prefix with a host suffix composed entirely of binary 1s. For example, the destination address used for a directed broadcast to devices on the 192.0.2.0/24 network is 192.0.2.255
multicast - address associated with a group of interested receivers. In IPv4, addresses 224.0.0.0 through 239.255.255.255 are designated as multicast addresses. The sender sends a single datagram from its unicast address to the multicast group address and the intermediary routers take care of making copies and sending them to all receivers that have joined the corresponding multicast group.

Private address range

Following address ranges are reserved for private addressing. These addresses are not routed in global routing table and should be translated to global address with network address translation (NAT):

10.0.0.0/8 - start: 10.0.0.0; end: 10.255.255.255
172.16.0.0/12 - start: 172.16.0.0; end:172.31.255.255
192.168.0.0/16 - start: 192.168.0.0; end: 192.168.255.255

Adding IP address

Consider setup where two routers are directly connected with the cable adn we do not want to waste address space

R1 configuration:
?

1 2	`/ip` `address` `add` `address=10.1.1.1/32` `interface=ether1 network=172.16.1.1`

R2 configuration:
?

1 2	`/ip` `address` `add` `address=172.16.1.1/32` `interface=ether1 network=10.1.1.1`

ARP TODO

Address Resolution Protocol (ARP) is a protocol for mapping an Internet Protocol (IP) address of host in the local network to the hardware address (MAC address). Each network device 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.

RouterOS implements ARP protocol according to RFC 826.

IPv6 Addressing

Internet Protocol version 6 (IPv6) is the new version of the Internet Protocol (IP). It was initially expected to replace IPv4 in short enough time, but for now it seems that these two version will coexist in Internet in foreseeable future. Nevertheless, IPv6 becomes more important, as the date of unallocated IPv4 address pool's exhaustion approaches.

The two main benefits of IPv6 over IPv4 are:

much larger address space;
support of stateless and statefull address autoconfiguration;
built-in security;
new header format (faster forwarding).

IPv6 uses 16 bytes addresses compared to 4 byte addresses in IPv4. IPv6 address syntax and types are described in RFC 4291.

There are multiple IPv6 address types, that can be recognized by their prefix. RouterOS distinguishes the following:

multicast (with prefix ff00::/8)
link-local (with prefix fe80::/10)
loopback (the address ::1/128)
unspecified (the address ::/128)
other (all other addresses, including the obsoleted site-local addresses, and RFC 4193 unique local addresses; they all are treated as global unicast).

One difference between IPv6 and IPv4 addressing is that IPv6 automatically generates a link-local IPv6 address for each active interface that has IPv6 support.

IPv6 addresses are represented a little bit different than IPv4 addresses. For IPv6, the 128-bit address is divided in eight 16-bit blocks, and each 16-bit block is converted to a 4-digit hexadecimal number and separated by colons. The resulting representation is called colon-hexadecimal.

In example above IPv6 address in binary format is converted to colon-hexadecimal representation

0010000000000001 0000010001110000 0001111100001001 0000000100110001
0000000000000000 0000000000000000 0000000000000000 0000000000001001

2001:0470:1f09:0131:0000:0000:0000:0009

IPv6 address can be further simplified by removing leading zeros in each block:

2001:470:1f09:131:0:0:0:9

As you can see IPv6 addresses can have long sequences of zeros. These contiguous sequence can be compressed to ::

2001:470:1f09:131::9

Note: Zero compression can only be used once. Otherwise, you could not determine the number of 0 bits represented by each instance of a double-colon

IPv6 prefix is written in address/prefix-length format. Compared to IPv4 decimal representation of network mask cannot be used. Prefix examples:

2001:470:1f09:131::/64
2001:db8:1234::/48
2607:f580::/32
2000::/3

Address Types

Several IPv6 address types exist:

Unicast
Anycast
Multicast

As you can see there are no Broadcast addresses in ipv6 network, compared to IPv4 broadcast functionality was completely replaced with multicast.

Unicast Addresses

Packets addressed to a unicast address are delivered only to a single interface. To this group belong:

globally unique addresses and can be used to connect to addresses with global scope anywhere.
link-local addresses
site-local addresses (FEC0::/48) - deprecated
special purpose addresses
compatibility addresses

Global unicast address can be automatically assigned to the node by Stateless Address auto-configuration.

Link-local Address

A link-local address is required on every IPv6-enabled interface, applications may rely on the existence of a link-local address even when there is no IPv6 routing, that is why link-local address is generated automatically for every active interface using it's interface identifier (calculated EUI-64 from MAC address if present). Address prefix is always FE80::/64 and IPv6 router never forwards link-local traffic beyond the link.

These addresses are comparable to the auto-configuration addresses 169.254.0.0/16 of IPv4.

A link-local address is also required for IPv6 Neighbor Discovery processes.
Note: If interface is set as bridge port, interface specific link-local address is removed leaving only bridge link-local address

Special Purpose Address

Address	Description
Unspecified address (::/128)	Never assigned to an interface or used as a destination address, used only to indicate the absence of an address. Equivalent to IPv4 0.0.0.0 address.
loopback address (::1/128)	Used to identify a loopback interface, enabling a node to send packets to itself. It is equivalent to the IPv4 loopback address of 127.0.0.1.

Compatibility Address

Address	Description
IPv4 compatible address	used by dual-stack nodes that are communicating with IPv6 over an IPv4 infrastructure. When the IPv4-compatible address is used as an IPv6 destination, IPv6 traffic is automatically encapsulated with an IPv4 header and sent to the destination by using the IPv4 infrastructure. Address is written in following format `::w.x.y.z`, where w.x.y.z is the dotted decimal representation of a public IPv4 address.
IPv4 mapped address	used to represent an IPv4-only node to an IPv6 node. It is used only for internal representation. The IPv4-mapped address is never used as a source or destination address for an IPv6 packet. The IPv6 protocol does not support the use of IPv4-mapped addresses. Address is written in following format: `::ffff:w.x.y.z`, where `w.x.y.z` is the dotted decimal representation of a public IPv4 address.
2002::/16	This prefix is used for 6to4 addressing. Here, an address from the IPv4 network 192.88.99.0/24 is also used.

Multicast Address

Most important multicast aspects are:

traffic is sent to a single address but is processed by multiple hosts;
group membership is dynamic, allowing hosts to join and leave the group at any time;
in IPv6, Multicast Listener Discovery (MLD) messages are used to determine group membership on a network segment, also known as a link or subnet;
host can send traffic to the group's address without belonging to the corresponding group.

A single IPv6 multicast address identifies each multicast group. Each group's reserved IPv6 address is shared by all host members of the group who listen and receive any IPv6 messages sent to the group's address.

Multicast address consists of the following parts:

The first 8 bits in multicast address is always 1111 1111 (which is FF in hexadecimal format).
Flag uses the 9th to 12th bit and shows if this multicast address is predefined (well-known) or not. If it is well-known, all bits are 0s.
Scope ID indicates to which scope multicast address belongs, for example, Scope ID=2 is link-local scope.
Group ID is used to specify a multicast group. There are predefined group IDs, such as Group ID=1 - all nodes. Therefore, if multicast address is ff02::1, that means Scope ID=2 and Group ID=1, indicating all nodes in link-local scope. This is analogous to broadcast in IPv4.

Here is the table of reserved IPV6 addresses for multicasting:

Address	Description
FF02::1	The all-nodes address used to reach all nodes on the same link.
FF02::2	The all-routers address used to reach all routers on the same link.
FF02::5	The all-Open Shortest Path First (OSPF) routers address used to reach all OSPF routers on the same link.
FF02::6	The all-OSPF designated routers address used to reach all OSPF designated routers on the same link.
FF02::1:FFXX:XXXX	The solicited-node address used in the address resolution process to resolve the IPv6 address of a link-local node to its link-layer address. The last 24 bits (XX:XXXX) of the solicited-node address are the last 24 bits of an IPv6 unicast address.

The following table is a partial list of IPv6 multicast addresses that are reserved for IPv6 multicasting and registered with the Internet Assigned Numbers Authority (IANA). For complete list of assigned addresses read IANA document.

Multicast addresses can be used to discover nodes in a network. For example, discover all nodes

mrz@bumba:/media/aaa/ver$ ping6 ff02::1%eth0
PING ff02::1%eth0(ff02::1) 56 data bytes
64 bytes from fe80::21a:4dff:fe5d:8e56: icmp_seq=1 ttl=64 time=0.037 ms
64 bytes from fe80::20c:42ff:fe0d:2c38: icmp_seq=1 ttl=64 time=4.03 ms (DUP!)
64 bytes from fe80::20c:42ff:fe28:7945: icmp_seq=1 ttl=64 time=5.59 ms (DUP!)
64 bytes from fe80::20c:42ff:fe49:fce5: icmp_seq=1 ttl=64 time=5.60 ms (DUP!)
64 bytes from fe80::20c:42ff:fe21:f1ec: icmp_seq=1 ttl=64 time=5.88 ms (DUP!)
64 bytes from fe80::20c:42ff:fe72:a1b0: icmp_seq=1 ttl=64 time=6.70 ms (DUP!)

discover all routers

mrz@bumba:/media/aaa/ver$ ping6 ff02::2%eth0
PING ff02::2%eth0(ff02::2) 56 data bytes
64 bytes from fe80::20c:42ff:fe28:7945: icmp_seq=1 ttl=64 time=0.672 ms
64 bytes from fe80::20c:42ff:fe0d:2c38: icmp_seq=1 ttl=64 time=1.44 ms (DUP!)

Anycast Address

Anycast address is a new type of address incorporated in IPv6.

Anycasting is a new networking paradigm supporting service–oriented Addresses where an identical address can be assigned to multiple nodes providing a specific service. An anycast packet (i.e., one with an anycast destination address) is delivered to one of these nodes with the same anycast address.

Anycast address is not assigned a specific address range. It is assigned from unicast address range.

Interface Identifier

The last 64 bits of an IPv6 address are the interface identifier that is unique to the 64-bit prefix of the IPv6 address. There are several ways how to determine interface identifier:

EUI-64;
randomly generated to provide a level of anonymity;
manually configured.

EUI-64

Traditional interface identifiers for network adapters are 48-bit MAC address. This address consists of a 24-bit manufacturer ID and a 24-bit board ID.

IEEE EUI-64 is a new standard for network interface addressing. The company ID is still 24-bits in length, but the extension ID is 40 bits, creating a much larger address space for a network adapters.

To create an EUI-64 address from the interface MAC address:

0xFFFE is inserted into the MAC address between the manufacturer ID and the board ID.
seventh bit of the first byte is reversed.

Lets make an example with following MAC address 00:0C:42:28:79:45.

mage above illustrates conversation process. When the result is converted to colon-hexadecimal notation, we get the interface identifier 20C:42FF:FE28:7945. As the result, corresponds link-local address is

FE80::20C:42FF:FE28:7945/64

In RouterOS, if the eui-64 parameter of an address is configured, the last 64 bits of that address will be automatically generated and updated using interface identifier. The last bits must be configured to be zero for this case. Example:

[admin@MikroTik] > ipv6 address add address=fc00:3::/64 interface=ether3 eui-64=yes
[admin@MikroTik] > ipv6 address print
Flags: X - disabled, I - invalid, D - dynamic, G - global, L - link-local
#    ADDRESS                                     INTERFACE                  ADVERTISE
...
5  G fc00:3::20c:42ff:fe1d:3d4/64                ether3                     yes
[admin@MikroTik] > interface ethernet set ether3 mac-address=10:00:00:00:00:01
[admin@MikroTik] > ipv6 address print
Flags: X - disabled, I - invalid, D - dynamic, G - global, L - link-local
#    ADDRESS                                     INTERFACE                  ADVERTISE
...
5  G fc00:3::1200:ff:fe00:1/64                   ether3                     yes

Configuring IPv6 Address

This example shows how to set up simple addressing with global IPv6 addresses between two routers.