I am working on converting my core to IPv6. My current addressing scheme includes the VLAN in the IPv6 address:

VLAN1511: XXXX:XXXX:XXXX:1511::1/64

However I have some VLAN overlap (the same VLAN number used in different locations/equipment for different roles) between my peering VLANS and customer VLANs. Therefore I can't use the "VLAN in address" scheme. I am wondering if it is OK practice to use ULA address for all the peering and Global for the customer (and internet) facing VLANs? I've heard people recommend and argue against both using ULA for peering and not, however I've never seen/heard any facts as to why.

Any thoughts welcome! Thanks!

  • How do you have overlap between Global IPv6 addressing? ULA addressing cannot be routed on the the Internet, so you would need the cooperation of the peers to use it for peering. The whole point of IPv6 is that the address space is large enough that you should never have any overlap. You probably need to rethink your addressing scheme. You should have plenty of bits. Studies have indicated that the average company readdresses three times when developing an IPv6 address scheme.
    – Ron Maupin
    May 3, 2017 at 23:35
  • Hello, thank you for the quick reply! Sorry for the confusion. I will encounter overlap if I use an addressing scheme where the VLAN is in the address and the VLAN is used in multiple locations and requires unique addressing. Example: If I use VLAN1000 for peering between a customer firewall and router, the address would be X:X:X:1000::0/128 and then use VLAN1000 for some customer servers, it would also be addressed with X:X:X:1000::0/64. Thankfully I have full control over all equipment (university environment) so coopartion from peers isn't' an issue because I am the peer :) May 3, 2017 at 23:42
  • You can use some of the bits to distinguish locations. You can search this site, and others, to find some sample IPv6 addressing schemes. It is smart to use the higher-order bits to determine the site.
    – Ron Maupin
    May 3, 2017 at 23:44
  • I had considered coding location into the address and I actually have a value for location and link-type in my ULA scheme. However we "only" have a /48 global allocation from our provider (CENIC). With a /48 I only have 4 characters to customize if I want to keep my prefixes SLAAC'able. In my organization the VLAN ID represents a lot of additional information in a convenient package, this is why I am trying to stick to a scheme where the VLAN ID can be used in the address. May 3, 2017 at 23:57
  • You should use a /48 for each site. ISPs will not advertise any prefix longer than /48, and it is simple to get a /48 address for each site. You need to clear the whole IPv4 thinking out of your head. There is no address shortage with IPv6, and you can get far more addressing than you need today.
    – Ron Maupin
    May 4, 2017 at 0:00

1 Answer 1


IPv6 allows you to have far more addressing than you actually need. If your business has multiple sites, you should have /48 networks for each site. You can get a much smaller, provider-independent prefix directly from your RIR, and you can use this prefix regardless of the ISP(s) used, and you can easily change ISPs.

You can then develop an IPv6 addressing scheme that takes into account your site. Use a couple of nibbles as a site ID. Use one or more other nibbles for various type of identification. For example, you may have a nibble to identify the network address type (e.g. router loopback, point-to-point link, VoIP network, User VLAN, Wi-Fi VLAN, etc.). You have great flexibility with the expanded IPv6 address space that you simply do not have with the limited IPv4 address space.

There are all sorts of IPv6 addressing schemes if you search for them, but only you can determine what works for you. I would recommend spending some time designing a good address scheme, and be sure to leave lots of space for future growth. Most companies will readdress multiple times as they come to terms with what can be done with the expanded address space, and a some serious forethought may prevent that.

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