IPv6 Addressing¶

IPv6 is the sixth-generation Internet protocol designed to replace IPv4. It provides a massive address space (\(2^{128}\) addresses) and modern capabilities for the future of the Internet.

Address Structure¶

Basic Format¶

An IPv6 address has 128 bits, represented as 8 groups of 4 hexadecimal digits separated by colons:

2001:0db8:85a3:0000:0000:8a2e:0370:7334

Abbreviation Rules¶

Rule 1: Omit Leading Zeros¶

Leading zeros in each group can be removed:

2001:db8:85a3:0:0:8a2e:370:7334

Rule 2: Compress Consecutive Zeros¶

One consecutive block of zeros can be replaced by :: (only once per address):

2001:db8:85a3::8a2e:370:7334

Abbreviation Examples¶

Full Address	Shortened	Notes
2001:0db8:0000:0000:0000:0000:0000:0001	2001:db8::1	Loopback
0000:0000:0000:0000:0000:0000:0000:0001	::1	Short loopback
0000:0000:0000:0000:0000:0000:0000:0000	::	Unspecified address

IPv6 Address Types¶

1. Unicast¶

Addresses that identify a single interface.

Global Unicast¶

Range: 2000::/3
Use: Public Internet
Example: 2001:db8:85a3::8a2e:370:7334

Global Unicast structure:

| 3 bits | 13 bits | 32 bits | 16 bits | 64 bits |
| Prefix | TLA ID | Reserved | SLA ID | Interface ID |

Link-Local Unicast¶

Range: fe80::/10
Use: Communication on the same link
Example: fe80::1%eth0
Autoconfiguration: Generated automatically by hosts

Unique Local Unicast (ULA)¶

Range: fc00::/7
Use: Private local networks
Example: fd12:3456:789a::1
Not routable on the Internet: Similar to RFC 1918 in IPv4

2. Multicast¶

Addresses that identify multiple interfaces.

Range: ff00::/8
Common groups:
ff02::1 — All nodes on the link
ff02::2 — All routers on the link
ff05::2 — All OSPF routers
ff02::1:ffxx:xxxx — Solicited-node (neighbor solicitation)

3. Anycast¶

Addresses assigned to multiple interfaces where traffic is delivered to the nearest one.

Use: Distributed services (DNS, NTP)
Syntax: Indistinguishable from unicast

Interface ID and EUI-64¶

Generating an Interface ID¶

In IPv6, the lower 64 bits identify the interface. They can be generated in several ways.

EUI-64 (Extended Unique Identifier)¶

Take the MAC address (48 bits).
Insert ffff in the middle: aa:bb:cc:ff:ff:dd:ee:ff.
Flip the U/L bit of the first octet.

def eui64_from_mac(mac):
    mac_parts = mac.split(':')
    eui64 = mac_parts[:3] + ['ff', 'ff'] + mac_parts[3:]
    first_byte = int(eui64[0], 16)
    first_byte ^= 0x02  # Flip U/L bit
    eui64[0] = f"{first_byte:02x}"
    return ':'.join(eui64)

print(eui64_from_mac("00:1B:44:11:3A:B7"))  # 021b:44ff:fe11:3ab7

Stateless Autoconfiguration (SLAAC)¶

Hosts generate the Interface ID automatically.
Based on MAC or random value for privacy.

IPv6 Configuration¶

Linux Commands¶

Show IPv6 addresses¶

ip -6 addr show
ip addr show dev eth0

Configure static address¶

ip addr add 2001:db8::1/64 dev eth0

Configure gateway¶

ip -6 route add default via 2001:db8::1 dev eth0

Configure /etc/network/interfaces¶

iface eth0 inet6 static
    address 2001:db8:85a3::8a2e:370:7334
    netmask 64
    gateway 2001:db8:85a3::1

Router Advertisements (RA)¶

Routers announce prefixes automatically:

# View received RAs
radvdump

IPv4/IPv6 Migration¶

Transition Techniques¶

Dual Stack¶

Hosts have both IPv4 and IPv6 addresses.
Applications choose the protocol.

Tunneling¶

6to4: 2002:ipv4_addr::/48
Teredo: Hosts behind IPv4 NAT
ISATAP: Intra-site tunneling

Translation¶

NAT64/DNS64: Protocol translation
SIIT: Stateless IP/ICMP translation

Configuration Examples¶

Dual Stack in Apache¶

Listen [::]:80
Listen 0.0.0.0:80

IPv6 in Docker¶

version: '3.8'
services:
  web:
    image: nginx
    ports:
      - "80:80"
      - "[::]:80:80"  # IPv6

IPv6 Security¶

IPv6-Specific Considerations¶

Autoconfiguration: Spoofing risk.
Extension Headers: Possible fragmentation abuse.
Multicast: Amplification vector.
Privacy Extensions: Temporary addresses.

Best Practices¶

Filtering: Apply IPv6 ACLs.
Monitoring: Use tools such as tcpdump.
Patching: Keep systems updated.

Diagnostic Tools¶

# IPv6 ping
ping6 2001:db8::1

# IPv6 traceroute
traceroute6 google.com

# Show IPv6 routes
ip -6 route show

# Show IPv6 neighbors
ip -6 neigh show

References¶

RFC 4291: IP Version 6 Addressing Architecture
RFC 4862: IPv6 Stateless Address Autoconfiguration
RFC 4941: Privacy Extensions for Stateless Address Autoconfiguration
RFC 7343: An IPv6 Prefix for Overlay Routable Cryptographic Hash Identifiers (ORCHIDv2)