IPv6Interface Config

ipv6 address [prefix/64] eui-64

Configures an IPv6 address on an interface using the EUI-64 format, which automatically generates the interface ID from the MAC address, commonly used for stateless address autoconfiguration (SLAAC).

Syntax·Interface Config

ipv6 address [prefix/64] eui-64

When to Use This Command

Assigning a link-local or global unicast IPv6 address to a router interface for SLAAC-based networks.
Configuring IPv6 on a LAN interface where hosts will use SLAAC to obtain their addresses.
Enabling IPv6 routing on a router interface with minimal manual addressing effort.
Setting up a point-to-point link with EUI-64 addresses for automatic interface ID generation.

Command Examples

Basic EUI-64 address configuration on GigabitEthernet0/0

ipv6 address 2001:db8:1:1::/64 eui-64

Router(config-if)# ipv6 address 2001:db8:1:1::/64 eui-64
Router(config-if)# end
Router# show ipv6 interface gigabitethernet 0/0
GigabitEthernet0/0 is up, line protocol is up
  IPv6 is enabled, link-local address is FE80::20C:29FF:FE8A:4B2C
  No Virtual link-local address(es):
  Global unicast address(es):
    2001:DB8:1:1:20C:29FF:FE8A:4B2C, subnet is 2001:DB8:1:1::/64 [EUI]
  Joined group address(es):
    FF02::1
    FF02::1:FF8A:4B2C
  MTU is 1500 bytes
  ICMP error messages limited to one every 100 milliseconds
  ICMP redirects are enabled
  ND DAD is enabled, number of DAD attempts: 1
  ND reachable time is 30000 milliseconds (using 30000)
  ND NS retransmit interval is 1000 milliseconds

The command assigns a global unicast address with prefix 2001:db8:1:1::/64. The EUI-64 process uses the MAC address (e.g., 00:0C:29:8A:4B:2C) to generate the interface ID 20C:29FF:FE8A:4B2C. The output shows the resulting global address and its subnet. The link-local address is also automatically derived from the same MAC.

Verifying EUI-64 address on a serial interface

ipv6 address 2001:db8:2:2::/64 eui-64

Router(config-if)# ipv6 address 2001:db8:2:2::/64 eui-64
Router(config-if)# do show ipv6 interface serial 0/0/0
Serial0/0/0 is up, line protocol is up
  IPv6 is enabled, link-local address is FE80::20C:29FF:FE8A:4B2C
  No Virtual link-local address(es):
  Global unicast address(es):
    2001:DB8:2:2:20C:29FF:FE8A:4B2C, subnet is 2001:DB8:2:2::/64 [EUI]
  Joined group address(es):
    FF02::1
    FF02::1:FF8A:4B2C
  MTU is 1500 bytes
  ICMP error messages limited to one every 100 milliseconds
  ICMP redirects are enabled
  ND DAD is enabled, number of DAD attempts: 1
  ND reachable time is 30000 milliseconds (using 30000)
  ND NS retransmit interval is 1000 milliseconds

On a serial interface, the EUI-64 address is generated similarly. The output confirms the global unicast address and its subnet. Note that the link-local address remains the same across interfaces if the same MAC is used (common on routers with a single MAC for all interfaces).

Understanding the Output

The 'show ipv6 interface' output displays the IPv6 configuration for a specific interface. Key fields include: 'IPv6 is enabled' indicates IPv6 is active; 'link-local address' is the automatically derived FE80:: address; 'Global unicast address(es)' shows the configured global address with its subnet and the [EUI] tag confirming EUI-64 format; 'Joined group address(es)' lists multicast groups the interface belongs to, including the solicited-node multicast group (FF02::1:FFxx:xxxx) used for Neighbor Discovery. A good configuration shows a valid global address with correct prefix length. Watch for duplicate address detection (DAD) failures or missing global address, which indicate misconfiguration or duplicate MAC issues.

CCNA Exam Tips

Remember that EUI-64 inserts FFFE in the middle of the MAC address and flips the U/L bit (7th bit) to 1.

CCNA may ask to calculate the EUI-64 interface ID from a given MAC address (e.g., MAC 00:1C:58:AB:CD:EF becomes 021C:58FF:FEAB:CDEF).

The command is used in interface configuration mode; you must first enter 'interface' mode.

EUI-64 addresses are commonly used with SLAAC; the router can advertise the prefix via Router Advertisements.

Common Mistakes

Forgetting to enable IPv6 globally with 'ipv6 unicast-routing' before configuring interface addresses.

Using the wrong prefix length (must be /64 for EUI-64 to work correctly).

Assuming the link-local address is manually configurable with this command; link-local is automatically generated.

Related Commands

ipv6 address [prefix/len]

Assigns a global unicast or link-local IPv6 address to an interface, enabling IPv6 routing on that interface.

ipv6 unicast-routing

Enables IPv6 unicast routing on a Cisco router, allowing it to forward IPv6 packets and participate in IPv6 routing protocols.

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