IPv6 DHCP Client (DHCPv6) in RouterOS: A Complete Guide

IPv6 DHCP Client (DHCPv6) in RouterOS: A Complete Guide

RouterOS Version: 7.x+ Difficulty: Intermediate Estimated Time: 30 minutes

Overview

The IPv6 DHCP client (DHCPv6) enables automatic IPv6 address and prefix acquisition from upstream providers. Unlike IPv4 DHCP which provides addresses, gateway, and DNS together, IPv6 splits these responsibilities:

• DHCPv6 provides addresses (IA_NA) and/or prefix delegation (IA_PD)
• Router Advertisements (RA) provide the default gateway
• DNS can come from either DHCPv6 or RA

The most common use case is Prefix Delegation (DHCP-PD), where your ISP delegates a block of addresses (typically /48, /56, or /60) that you can distribute across your internal networks.

Critical concept: DHCPv6 does NOT provide default gateway information. You MUST enable Router Advertisement acceptance (accept-router-advertisements=yes) for IPv6 internet connectivity.

Prerequisites

Before configuring DHCPv6:

1. Enable the IPv6 package:

   /system package enable ipv6
   /system reboot

2. Verify package is active:

   /system package print where name=ipv6

How IPv6 Address Assignment Works

┌─────────────────────────────────────────────────────────────────────┐
│                           ISP Network                                │
│                                                                      │
│   DHCPv6 Server ─────────────── Router Advertisement ────────────   │
│   (Prefix Delegation)          (Default Gateway)                     │
└─────────────────────────────────────────────────────────────────────┘
              │                            │
              │ Prefix: 2001:db8::/56      │ Gateway: fe80::1
              ▼                            ▼
┌─────────────────────────────────────────────────────────────────────┐
│                        Your MikroTik Router                          │
│                                                                      │
│   DHCPv6 Client ──▶ IPv6 Pool ──▶ LAN Addresses                     │
│   (ether1-wan)      (isp-pool)   (bridge: ::1/64 from pool)         │
└─────────────────────────────────────────────────────────────────────┘
              │
              │ RA with prefix 2001:db8:0:1::/64
              ▼
┌─────────────────────────────────────────────────────────────────────┐
│                         LAN Devices                                  │
│            (SLAAC: 2001:db8:0:1:xxxx:xxxx:xxxx:xxxx)                │
└─────────────────────────────────────────────────────────────────────┘

Menu Reference

Menu	Purpose
/ipv6 dhcp-client	DHCPv6 client configuration
/ipv6 pool	IPv6 address pools (auto-created by PD)
/ipv6 address	IPv6 addresses (use from-pool for PD)
/ipv6 settings	Global IPv6 settings (RA acceptance)

Configuration Properties

Property	Type	Default	Description
interface	string	-	WAN interface for DHCPv6 (required)
request	prefix, address	-	What to request from server
pool-name	string	-	Pool name to store delegated prefix
pool-prefix-length	integer	-	Size of allocations from pool (typically 64)
prefix-hint	IPv6 prefix	-	Preferred prefix size hint to ISP (e.g., ::/56)
add-default-route	yes/no	no	Add default route from DHCPv6 (NOT recommended)
use-peer-dns	yes/no	yes	Accept DNS servers from DHCPv6
disabled	yes/no	no	Enable/disable client

Configuration Examples

Example 1: Basic Prefix Delegation (Most Common)

This is the standard residential/SMB setup:

# Step 1: Enable Router Advertisement acceptance (CRITICAL)
/ipv6 settings set accept-router-advertisements=yes

# Step 2: Create DHCPv6 client for prefix delegation
/ipv6 dhcp-client add interface=ether1-wan request=prefix \
    pool-name=isp-pool pool-prefix-length=64

# Step 3: Verify prefix received
/ipv6 dhcp-client print

Expected output:

 #  INTERFACE    STATUS  PREFIX
 0  ether1-wan   bound   2001:db8:abcd::/56

# Step 4: Assign address to LAN from pool
/ipv6 address add address=::1/64 from-pool=isp-pool interface=bridge advertise=yes

# Step 5: Verify default route (comes from RA, not DHCPv6)
/ipv6 route print where dst-address="::/0"

Expected: Route with fe80::... gateway (link-local address is normal).

Example 2: DHCPv6 over PPPoE

For ISPs using PPPoE with IPv6:

# Step 1: Create PPPoE client
/interface pppoe-client add name=pppoe-wan interface=ether1 \
    user=myuser password=mypass

# Step 2: Enable RA acceptance
/ipv6 settings set accept-router-advertisements=yes

# Step 3: Create DHCPv6 client on PPPoE interface
/ipv6 dhcp-client add interface=pppoe-wan request=prefix \
    pool-name=pppoe-pool pool-prefix-length=64

# Step 4: Assign LAN address from pool
/ipv6 address add address=::1/64 from-pool=pppoe-pool interface=bridge advertise=yes

Example 3: Request Both Address and Prefix

Some ISPs provide both a WAN address and a delegated prefix:

/ipv6 dhcp-client add interface=ether1-wan request=address,prefix \
    pool-name=isp-pool pool-prefix-length=64 use-peer-dns=yes

Verify both were received:

/ipv6 dhcp-client print detail

Look for both address and prefix fields populated.

Example 4: Multiple VLANs from Delegated Prefix

When ISP provides a larger prefix (/48 or /56), distribute across VLANs:

# Step 1: Request prefix with size hint
/ipv6 dhcp-client add interface=ether1-wan request=prefix \
    pool-name=isp-pool pool-prefix-length=64 prefix-hint=::/56

# Step 2: Assign to multiple VLANs (each gets unique /64)
/ipv6 address add address=::1/64 from-pool=isp-pool interface=vlan10 advertise=yes
/ipv6 address add address=::1/64 from-pool=isp-pool interface=vlan20 advertise=yes
/ipv6 address add address=::1/64 from-pool=isp-pool interface=vlan30 advertise=yes

# Step 3: Verify each VLAN got different /64
/ipv6 address print where from-pool=isp-pool

Example 5: Custom DNS (Ignore ISP DNS)

/ipv6 dhcp-client add interface=ether1-wan request=prefix \
    pool-name=isp-pool pool-prefix-length=64 use-peer-dns=no

# Set custom DNS
/ip dns set servers=2606:4700:4700::1111,2606:4700:4700::1001

Example 6: DHCPv6 Status Change Script

Execute a script when prefix is acquired or lost:

/ipv6 dhcp-client add interface=ether1-wan request=prefix \
    pool-name=isp-pool pool-prefix-length=64 script={
        :if ($"pd-valid" = 1) do={
            :log info "DHCPv6: Prefix acquired: $\"pd-prefix\""
            # Add custom actions here
        } else={
            :log warning "DHCPv6: Prefix lost!"
            # Add recovery actions here
        }
    }

Available script variables:

Variable	Description
pd-valid	1 = prefix valid, 0 = prefix removed
pd-prefix	The delegated prefix (e.g., 2001:db8::/56)
na-valid	1 = address valid, 0 = address removed
na-address	The assigned IPv6 address

Example 7: Firewall Rule for DHCPv6 Client

Ensure firewall allows DHCPv6 client traffic:

/ipv6 firewall filter add chain=input dst-port=546 protocol=udp \
    action=accept comment="Allow DHCPv6 client" place-before=0

Note: Some ISPs send DHCPv6 from global addresses (not link-local). If using a firewall rule with src-address=fe80::/10, change it to in-interface=ether1-wan instead.

Understanding pool-prefix-length vs prefix-hint

These are commonly confused:

Property	Purpose	Example
prefix-hint	Tell ISP what size prefix you want	::/56 requests a /56
pool-prefix-length	Size of allocations FROM the pool	64 means pool gives out /64s

Example: ISP gives you a /56. You want to assign /64s to each VLAN:

/ipv6 dhcp-client add interface=ether1-wan request=prefix \
    pool-name=isp-pool \
    prefix-hint=::/56 \          # Request /56 from ISP
    pool-prefix-length=64        # Allocate /64s from pool

Common Problems and Solutions

Problem 1: No Internet Despite “Bound” Status

Symptom: DHCPv6 shows bound but no IPv6 connectivity.

Cause: Missing default route because Router Advertisements are disabled.

Solution:

/ipv6 settings set accept-router-advertisements=yes

Verify:

/ipv6 route print where dst-address="::/0"

Should show route with fe80:: gateway.

Problem 2: Client Stuck on “Searching”

Causes:

1. Firewall blocking UDP port 546
2. ISP not providing DHCPv6
3. ISP device in gateway mode (not bridge)

Solutions:

# Add firewall rule
/ipv6 firewall filter add chain=input dst-port=546 protocol=udp action=accept place-before=0

# Check ISP provides DHCPv6 (contact ISP)
# Put ISP modem in bridge mode if possible

Problem 3: Firewall Blocks ISP’s DHCPv6 Server

Symptom: DHCPv6 works on some ISPs but not others.

Cause: Default firewall rule restricts DHCPv6 to link-local sources, but some ISPs (like Comcast) use global addresses.

Solution:

# Instead of: src-address=fe80::/10
# Use: in-interface=ether1-wan
/ipv6 firewall filter set [find comment~"DHCPv6"] in-interface=ether1-wan

Problem 4: Only One /64 Available from Large Prefix

Cause: pool-prefix-length not set or set incorrectly.

Solution:

/ipv6 dhcp-client set [find] pool-prefix-length=64

This ensures /64s are allocated from the pool (not the entire prefix as one block).

Problem 5: add-default-route=yes Causes Issues

Cause: This property is a workaround that often fails.

Solution:

# Don't use add-default-route
/ipv6 dhcp-client set [find] add-default-route=no

# Instead, enable RA acceptance
/ipv6 settings set accept-router-advertisements=yes

Problem 6: ISP DNS Still Used Despite use-peer-dns=no

Cause: DNS may also come from Router Advertisements.

Solution: Wait for prefix renewal, or release/renew:

/ipv6 dhcp-client release [find]
/ipv6 dhcp-client renew [find]

DHCPv6 Client Status Values

Status	Meaning
bound	Successfully acquired prefix/address
searching	Sending SOLICIT, waiting for server
requesting	Sent REQUEST, waiting for REPLY
renewing	Renewing lease with original server
rebinding	Trying to rebind with any server
stopped	Client is disabled
error	Error occurred

Verification Commands

# Check DHCPv6 client status
/ipv6 dhcp-client print detail

# Verify pool was created
/ipv6 pool print

# Check LAN addresses from pool
/ipv6 address print where from-pool

# Verify default route (from RA)
/ipv6 route print where dst-address="::/0"

# Check RA acceptance is enabled
/ipv6 settings print

# Test IPv6 connectivity
/ping 2001:4860:4860::8888 count=3

# Release and renew
/ipv6 dhcp-client release [find]
/ipv6 dhcp-client renew [find]

Key Differences from IPv4 DHCP

Aspect	IPv4 DHCP	IPv6 DHCPv6
Default Gateway	Provided by DHCP	Provided by Router Advertisement
Address Assignment	Always via DHCP	Can be DHCP, SLAAC, or both
Prefix Delegation	Not applicable	Common feature (DHCP-PD)
DNS	Provided by DHCP	Can be DHCP or RA

Related Features

• IPv6 Addresses (/ipv6 address) - Use from-pool for dynamic assignment
• IPv6 Pools (/ipv6 pool) - Stores delegated prefixes
• IPv6 ND (/ipv6 nd) - Configure Router Advertisements for LAN
• IPv6 Firewall (/ipv6 firewall) - Must allow UDP 546
• IPv6 Routes (/ipv6 route) - Default route comes from RA
• IPv6 Settings (/ipv6 settings) - Enable accept-router-advertisements

Summary

DHCPv6 in RouterOS is primarily used for Prefix Delegation from your ISP:

1. Enable IPv6 package and reboot
2. Enable RA acceptance (accept-router-advertisements=yes) - CRITICAL
3. Create DHCPv6 client with request=prefix
4. Assign LAN addresses using from-pool
5. Verify connectivity with ping to IPv6 address

Key points:

• DHCPv6 does NOT provide default gateway - that comes from Router Advertisements
• pool-prefix-length=64 is typically correct for LAN allocation
• prefix-hint is a request to ISP (may be ignored)
• Some ISPs require their modem/ONT in bridge mode for PD to work
• Link-local addresses (fe80::) as gateways are normal in IPv6

Related Topics

Prerequisites

• IPv6 Addresses - IPv6 address configuration basics

LAN Distribution

• IPv6 ND - configure Router Advertisements for LAN clients (SLAAC)
• IPv6 DHCP Server - serve addresses to LAN (if not using SLAAC)
• IPv6 DHCP Relay - relay DHCPv6 across network segments

Security

• IPv6 Firewall - must allow UDP port 546 for DHCPv6 client

Related Topics

• PPPoE Client - DHCPv6 often runs over PPPoE
• DNS Server - configure IPv6 DNS servers