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IPv6 loopbacks

All,

How can you create a loopback interface in IPv6 on a router that would allow you to simulate other networks?

I tried to run autoconfig on the loopback interface, but they get all of the same addressing. The address of ::1/128 is the loopback address, but to create multiple loopbacks, would ::2/128, ::3/128, etc. work?

Thanks,

John

HTH, John *** Please rate all useful posts ***
1 REPLY
Cisco Employee

Re: IPv6 loopbacks

John,

When you say that they all get the same address, you probably mean that the loopback interfaces have IPv6 addresses part of the FE80::/10. These are link local addresses as shown in the following document:

http://www.iana.org/assignments/ipv6-address-space

These addresses are assigned automatically to each interface and serve for communication between IPv6 devices on a local link.

As for ::1/128, you can't configure it on any interface and you should get the following message if you try:

Router(config-if)#ipv6 address ::1/128

%Loopback0: Error: ::1/128 is invalid

One more thing, you can't configure autoconfig on the loopback as this command assumes that there is another device on the subnet from which you can get autoconfiguration information.

Your best option would be to configure valid ipv6 addresses statically on the loopback interface(s) as follow:

for instance

int lo0

ipv6 address 2001:db8;12ff::1/128

or

ipv6 address 2001:db8;12ff::/64 eui-64

Regards

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
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