ipv6 addresses configuring as anycast by default

[notaciscoguy]

hello all,

I am running into an odd issue where I am attempting a dual-stack environment with a home lab. the devices are 2811 routers running various versions of IOS 12. when I configure IPv6 addresses on interfaces, I get warnings that say that anycast addresses shouldn't be configured on interfaces. I am not using the anycast switch at the end of my syntax, and I have enabled ipv6 unicast-routing in global config. my prefix is a permutation of fc30::/125, which I understand should be local unique addresses. the devices still accept the input, and I can successfully ping the interfaces via IPv6, but I am curious why they are defaulting to anycast instead of unicast. 

[Harold Ritter]

This is because you are using an all zeroes for the interface identifier part of the address (fc30::/125).

Try using fc30::1/125 instead.

Regards,

[notaciscoguy]

I should have been clearer. I am using FC30 as the basis for a larger block. the actual block range starts at FC30:1111::FFFF:0080/125 I've tried several different subnets, ranging from 0080 to 00B8, and various addresses from within those nets. 

[Harold Ritter · Accepted solution]

The issue is that you have a mask of 125 bit, therefore if the last 3 bit are set to 0, it will be considered a subnet router anycast. Try FC30:1111::FFFF:0081/125 or 82, 83, 84, 85, 86, 87 and you will not get the warning message.

Bear in mind that this message is just a warning and will not prevent the configuration of the ipv6 address.

Regards,