IPv6: Mikrotik: Router Advertisement RA

Summary

Sub-menu: ipv6 nd
Standards: RFC 2462, RFC 2461
Package: IPv6

RouterOS has Ipv6 Neighbor Detection and stateless address autoconfiguration support using Router Advertisement Daemon (RADVD).

Node description

Node is a device that implements IPv6. In IPv6 networks nodes are divided into two types:

• Routers - a node that forwards IPv6 packets not explicitly addressed to itself.
• Hosts - any node that is not a router.

Routers and hosts are strictly separated, meaning that router cannot be host and host cannot be router at the same time.

Stateless address autoconfiguration

There are several types of autoconfiguration:

• stateless - address configuration is done by received Router Advertisement messages. These messages include stateless address prefixes and require that host is not using stateful address configuration protocol.
• stateful - address configuration is done by using stateful address configuration protocol (DHCPv6). Stateful protocol is used if RA messages do not include address prefixes.
• both - RA messages include stateless address prefixes and require that hosts use a stateful address configuration protocol.

A highly useful feature of IPv6 is the ability to automatically configure itself without the use of a stateful configuration protocol like DHCP ( See example).

It is called stateless address autoconfiguration, since there is no need to manage state in the router side. It is a very simple, robust and effective autoconfiguration mechanism.

RouterOS uses RADVD to periodically advertise information about the link to all nodes on the same link. The information is carried by ICMPv6 "router advertisement" packet, and includes following fields:

• IPv6 subnet prefix
• Default router link local address
• Other parameters that may be optional: link MTU, default hoplimit, and router lifetime.

Then host catches the advertisement, and configures the global IPv6 address and the default router. Global IPv6 address is generated from advertised subnet prefix and EUI-64 interface identifier.

Optionally, the host can ask for an advertisement from the router by sending an ICMPv6 "router solicitation" packet. On linux rtsol utility transmits the router solicitation packet. If you are running a mobile node, you may want to transmit router solicitations periodically.

Address states

When auto-configuration address is assigned it can be in one of the following states:

• tentative - in this state host verifies that the address is unique. Verification occurs through duplicate address detection.
• preferred - at this state address is verified as unique and node can send and receive unicast traffic to and from a preferred address. The period of time of preferred state is included in the RA message.
• deprecated - address is still valid, but is not used for new connections.
• invalid - node can no longer send or receive unicast traffic. An address enters the invalid state after the valid lifetime expires.

Image belove ilustrates relation between states and lifetimes. File:Ipv6-lifetime.png

Neighbor discovery

ipv6 nd

In this submenu IPv6 Neighbor Discovery (ND) protocol is configured.

Neighbor Discovery (ND) is a set of messages and processes that determine relationships between neighboring nodes. ND, compared to IPv4, replaces Address Resolution Protocol (ARP), Internet Control Message Protocol (ICMP) Router Discovery, and ICMP Redirect and provides additional functionality.

ND is used by hosts to:

• Discover neighboring routers.
• Discover addresses, address prefixes, and other configuration parameters.

ND is used by routers to:

• Advertise their presence, host configuration parameters, and on-link prefixes.
• Inform hosts of a better next-hop address to forward packets for a specific destination.

ND is used by nodes to:

• Both resolve the link-layer address of a neighboring node to which an IPv6 packet is being forwarded and determine when the link-layer address of a neighboring node has changed.
• Determine whether IPv6 packets can be sent to and received from a neighbor.

Properties

• advertise-dns (yes | no; Default: no)
• advertise-mac-address (yes | no; Default: yes)
• comment (string; Default: )
• disabled (yes | no; Default: no)
• hop-limit (unspecified | integer[0..4294967295]; Default: unspecified)
• interface (all | string; Default: )
• managed-address-configuration (yes | no; Default: no)
• mtu (unspecified | integer[0..4294967295]; Default: unspecified)
• other-configuration (yes | no; Default: no)
• ra-delay (time; Default: 3s)
• ra-interval (time[3s..20m50s]-time[4s..30m]; Default: 3m20s-10m)
• ra-lifetime (none | time; Default: 30m)
• reachable-time (unspecified | time[0..1h]; Default: unspecified)
• retransmit-interval (unspecified | time; Default: unspecified)

Prefix

ipv6 nd prefix

Prefix information sent in RA messages used by stateless address auto-configuration.

Properties

• 6to4-interface (none | string; Default: )
• autonomous (yes | no; Default: yes)
• comment (string; Default: )
• disabled (yes | no; Default: no)
• on-link (yes | no; Default: yes)
• preferred-lifetime (infinity | time; Default: 1w)
• prefix (ipv6 prefix; Default: ::/64)
• valid-lifetime (infinity | time; Default: 4w2d)
• interface (string; Default: )

Examples

Stateless autoconfiguration example

[admin@MikroTik] > ipv6 address print
Flags: X - disabled, I - invalid, D - dynamic, G - global, L - link-local
 #    ADDRESS                                     INTERFACE         ADVERTISE
 0  G 2001:db8::1/64                                ether1            yes

As in example above advertise flag is enabled which indicates that dynamic /ipv6 nd prefix entry is added.

[admin@MikroTik] > ipv6 nd prefix print
Flags: X - disabled, I - invalid, D - dynamic
 0 D prefix=2001:db8::/64 interface=ether1 on-link=yes autonomous=yes
      valid-lifetime=4w2d preferred-lifetime=1w

On a host that is directly attached to the router we see that an address was added. The address consists of prefix part (first 64 bits) that takes prefix from the prefix advertisement, and host part (last 64 bits) that is automatically generated from local MAC address:

atis@atis-desktop:~$ ip -6 addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qlen 1000
    inet6 2001:db8::21a:4dff:fe56:1f4d/64 scope global dynamic
       valid_lft 2588363sec preferred_lft 601163sec
    inet6 fe80::21a:4dff:fe56:1f4d/64 scope link
       valid_lft forever preferred_lft forever

The host has received the 2001:db8::/64 prefix from the router and configured an address with it.

There is also an option to redistribute DNS server information using RADVD:

[admin@MikroTik] > ip dns set server=2001:db8::2
[admin@MikroTik] > ip dns print
          servers: 2001:db8::2
...
[admin@MikroTik] > ipv6 nd set [f] advertise-dns=yes

You will need a running client side software with Router Advertisement DNS support to take advantage of the advertised DNS information.

On Ubuntu/Debian linux distributions you can install rdnssd package which is capable of receiving advertised DNS address.

mrz@bumba:/$ sudo apt-get install rdnssd

mrz@bumba:/$ cat /etc/resolv.conf 
# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
#     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
nameserver 2001:db8::2

mrz@bumba:/$ ping6 www.mikrotik.com
PING www.mikrotik.com(2a02:610:7501:1000::2) 56 data bytes
64 bytes from 2a02:610:7501:1000::2: icmp_seq=1 ttl=61 time=2.11 ms
64 bytes from 2a02:610:7501:1000::2: icmp_seq=2 ttl=61 time=1.33 ms
^C
--- www.mikrotik.com ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1001ms
rtt min/avg/max/mdev = 1.334/1.725/2.117/0.393 ms
mrz@bumba:/$ 

Referensi

• https://wiki.mikrotik.com/wiki/Manual:IPv6/ND

Pranala Menarik

• IPv6: Mikrotik: ND / RA contoh konfigurasi