Assigning a 127-bit subnet mask to an IPv6 address

To conserve address space, you can assign a 127-bit subnet mask to an IPv6 address.

You can configure an IPv6 address with a 127-bit subnet mask on any interface.

  1. On device 1, enter global configuration mode. 
    device1# configure terminal
  2. Enter interface configuration mode. 
    device1(config)# interface ethernet 1/1/5
  3. Configure an IPv6 address with a 127-bit subnet mask. 
    device1(config-if-e1000-1/1/5)# ipv6 address 2001:1::0/127
  4. On device 2, enter global configuration mode. 
    device2# configure terminal
  5. Enter interface configuration mode. 
    device2(config)# interface ethernet 1/1/5
  6. Configure an IPv6 address with a 127-bit subnet mask. 
    device2(config-if-e1000-1/1/5)# ipv6 address 2001:1::1/127

The following example assigns a 127-bit subnet mask to an IPv6 address on two devices. 

device1# configure terminal
device1(config)# interface ethernet 1/1/5
device1(config-if-e1000-1/1/5)# ipv6 address 2001:1::0/127 

device2# configure terminal
device2(config)# interface ethernet 1/1/5
device2(config-if-e1000-1/1/5)# ipv6 address 2001:1::1/127
Parent topic: 127-Bit Subnet Masks on Point-to-Point Networks