Solved: Reserved Anycast Address

DJX995 · ‎10-05-2015

I setup my IPv6 address very similar to my IPv4 addresses.

In IPv4, I use the last address in a /24 as my L3 router (10.0.VLAN.254)

In IPv6, I use the last address in a /64 as my L3 router (XXXX:XXX:XXXX:VLAN:FFFF:FFFF:FFFF:FFFE)

This works fine, however my 3750X is telling me that my IPv6 is a reserved Anycast address.
"%VlanXXX: Warning: XXXX:XXX:XXXX:VLAN:FFFF:FFFF:FFFF:FFFE/64 is a Reserved Anycast"

My questions are:

Do I need to change this?

What are problems that might occur if I don't change anything?

Thanks!

Peter Paluch · ‎10-05-2015

Hello,

I would personally say that your setup is acceptable in terms of functionality - it currently works for you and you do not have any issues because you do not implement Mobile IPv6 in your network. However, it is always best to avoid using addresses that have already been reserved for a different purpose, just in case that in future, you may actually be deploying the feature that uses those addresses, and then you could start having trouble.

I would personally suggest avoiding these addresses in the future, and selecting a different set of addresses. One of possibilities is using XXXX:XXXX:XXXX:VLAN:FFFF:FFFF:FFFF:FF7F/64. This address is the highest IPv6 address that does not belong into the block of reserved anycast addresses in a subnet (the ...:FFFF:FFFF:FFFF:FF80 and higher are reserved).

Best regards,
Peter

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Peter Paluch · ‎10-05-2015

Hello,

According to RFC 2526 Section 3, the IPv6 address you are using corresponds to the address of Mobile IPv6 Home Agents. It could potentially cause clashes if you ever decided to deploy Mobile IPv6 in your network; however, to my best knowledge, there is no actively maintained Mobile IPv6 support in any common operating system (Windows, Linux, iOS). Practically speaking, a potential conflict or confusion of addresses is improbable.

My question, however, is: Are you sure you need the global IPv6 address on that particular interface, anyway?

Best regards,
Peter

DJX995 · ‎10-05-2015

I setup my IPv6 side just like my IPv4 side so that address is the default gateway for that VLAN.

I have a bunch of those addresses, one for each VLAN and I point my devices to that address as the default gateway.

Peter Paluch · ‎10-05-2015

Hi,

I have a bunch of those addresses, one for each VLAN and I point my devices to that address as the default gateway.

I understand. Of course, that is fine - please apologize my previous question, my thinking wasn't correct.

Best regards,
Peter

DJX995 · ‎10-05-2015

So my setup is fine as is?

Should I be usuing a different logic in the future?

Peter Paluch · ‎10-05-2015

Hello,

I would personally say that your setup is acceptable in terms of functionality - it currently works for you and you do not have any issues because you do not implement Mobile IPv6 in your network. However, it is always best to avoid using addresses that have already been reserved for a different purpose, just in case that in future, you may actually be deploying the feature that uses those addresses, and then you could start having trouble.

I would personally suggest avoiding these addresses in the future, and selecting a different set of addresses. One of possibilities is using XXXX:XXXX:XXXX:VLAN:FFFF:FFFF:FFFF:FF7F/64. This address is the highest IPv6 address that does not belong into the block of reserved anycast addresses in a subnet (the ...:FFFF:FFFF:FFFF:FF80 and higher are reserved).

Best regards,
Peter

DJX995 · ‎10-06-2015

I will do that.

Thanks.