{"id":2905,"date":"2016-02-27T19:03:02","date_gmt":"2016-02-27T19:03:02","guid":{"rendered":"https:\/\/live-infoblox-blog.pantheonsite.io\/?p=2905"},"modified":"2025-04-02T12:08:10","modified_gmt":"2025-04-02T19:08:10","slug":"3-ways-to-ruin-your-future-network-with-ipv6-unique-local","status":"publish","type":"post","link":"https:\/\/www.infoblox.com\/blog\/ipv6-coe\/3-ways-to-ruin-your-future-network-with-ipv6-unique-local\/","title":{"rendered":"3 Ways to Ruin Your Future Network with IPv6 Unique Local Addresses (Part 1 of 2)"},"content":{"rendered":"<p>To ULA or not to ULA. That is the question: Whether \u2018tis nobler in the mind to suffer the slings and arrows of multiple NATs&#8230;<\/p>\n<p>Ok, ok. I\u2019ll stop now (and in a moment, explain my lame joke to the uninitiated.) But first, in case you\u2019re wondering what exactly I\u2019ll be covering in this blog (i.e., whether you want to read it), I\u2019m going to review the critical details of IPv6 ULAs before offering some suggestions on the best and most proper uses of them. This will be at least partly accomplished by demonstrating three ways ULAs can be abused in ways that will almost certainly cause major headaches down the road.<\/p>\n<p><strong>Introduction<\/strong><\/p>\n<p>ULA, of course, is short for IPv6 Unique Local Addresses. Most of us gain our first, familiar understanding of <a href=\"https:\/\/www.infoblox.com\/glossary\/ipv6\/\" target=\"_blank\"><strong>IPv6<\/strong><\/a> ULAs when hearing them described (more or less) as the equivalent of IPv4 private addresses (RFC 1918). (A quick-and-dirty way to understand them is to think about what\u00a0<em>unique<\/em>\u00a0and\u00a0<em>local<\/em>\u00a0mean in this context:\u00a0<em>unique<\/em>\u00a0meaning no overlaps with others using the same address type and\u00a0<em>local<\/em>\u00a0meaning local to your company only.) If we\u2019re both new to IPv6 and used to running corporate LANs, it would be quite natural to imagine upon hearing such a description that we\u2019d soon be deploying these so-called private IPv6 ULAs and using NAT to translate to public IPv6 addresses (from the Global Unicast Address or GUA range) at the edge of the enterprise network. Fortunately, the relatively slow deployment of IPv6 among enterprises prevents this unforced error and by and by we learn that such a configuration is most definitely\u00a0<strong>not<\/strong>\u00a0recommended as a best practice (or 2<sup>nd<\/sup>\u00a0best practice, or even 3<sup>rd<\/sup>\u00a0best practice) for reasons we\u2019ll cover below.<\/p>\n<p>Ensuring your organization\u2019s <a href=\"https:\/\/www.infoblox.com\/solutions\/ipv6-readiness\/\" target=\"_blank\"><strong>IPV6 Network Readiness<\/strong><\/a> is essential for leveraging the full potential of modern network protocols and avoiding common pitfalls with ULA deployment.<\/p>\n<p><strong>Characteristics of IPv6 Unique Local Addresses (ULAs)<\/strong><\/p>\n<p>IPv6 ULAs have some particular characteristics, each with a caveat.<\/p>\n<ul>\n<li>They\u2019re considered global in scope \u2013 though as we\u2019ll see in a moment we have to be careful with how we interpret that scope description<\/li>\n<li>IPv6 ULAs are allocated from the fc00::\/7 subnet \u2013 though technically only from the bottom half (or is it the top half, the right or left half?) of fd00::\/8<\/li>\n<li>ULAs from this range have a randomly generated 40 bits \u2013 though in practice these 40 bits are often manually assigned to make them easier to remember<\/li>\n<\/ul>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-2907\" src=\"https:\/\/live-infoblox-blog.pantheonsite.io\/wp-content\/uploads\/unique-local-address-structure.png\" alt=\"Figure 1. Unique Local Address structure\" width=\"600\" height=\"256\" srcset=\"https:\/\/www.infoblox.com\/blog\/wp-content\/uploads\/unique-local-address-structure.png 600w, https:\/\/www.infoblox.com\/blog\/wp-content\/uploads\/unique-local-address-structure-300x128.png 300w\" sizes=\"auto, (max-width: 600px) 100vw, 600px\" \/><\/p>\n<p><em>Figure 1. Unique Local Address structure<\/em><\/p>\n<p>Gaining <a href=\"https:\/\/www.infoblox.com\/products\/network-insight\/\" target=\"_blank\"><strong>Network Insight<\/strong><\/a> into the usage of ULAs can help administrators prevent issues related to overlapping address spaces or improper configurations.<\/p>\n<p>According to RFC 4007 \u201cIPv6 Scoped Address Architecture,\u201d unicast IPv6 addresses are either link-local in scope and uniquely identify interfaces on only a single link (e.g., addresses derived from the prefix fe80::\/10) or they are global in scope and uniquely identify an interface anywhere on the Internet.<\/p>\n<p>Unique Local Addresses permit communication between nodes on different links and so certainly aren\u2019t link-local in scope. But their global scope is characteristically different than addresses from the actual Global Unicast Allocation (2000::\/3) in that ULAs are not currently indicated for routing on the Internet (you can review the IANA registries for IPv6 address types\u00a0<a href=\"http:\/\/www.iana.org\/assignments\/iana-ipv6-special-registry\/iana-ipv6-special-registry.xhtml#iana-ipv6-special-registry-1\" target=\"_blank\" rel=\"nofollow noopener noreferrer\">here<\/a>\u00a0and\u00a0<a href=\"http:\/\/www.iana.org\/assignments\/ipv6-unicast-address-assignments\/ipv6-unicast-address-assignments.xhtml\" target=\"_blank\" rel=\"nofollow noopener noreferrer\">here<\/a>). Instead, they are typically used in the way we first described them, as the equivalent of IPv4 private addresses; e.g., routed exclusively within an enterprise private network. Given this usage, their scope would appear to be somewhere between link-local and global.<\/p>\n<p>Incidentally, such a scope was formally defined. The site-local address allocation (fec0::\/10) was conceived to provide addressing exclusively within a site but has now been deprecated.<\/p>\n<p>The ULA prefix is fc00::\/7. But the 8<sup>th<\/sup>\u00a0most-significant-bit (MSB) determines which \u201chalf\u201d of the allocation a prefix is being assigned from, fc00::\/8 or fd00::\/8. According to the RFC 4193 \u201cUnique Local IPv6 Unicast Addresses,\u201d this bit indicates a locally assigned prefix when set to 1 and is undefined when set to 0. Thus, technically only prefixes from fd00::\/8 should be defined and used.<\/p>\n<p>As with the next characteristic, however, there is nothing preventing an administrator from bending the rules and defining and using a prefix from the fc00::\/8 portion of the allocation.<\/p>\n<p>Finally, the 40 bits defining any ULA prefix assigned from the fd00::\/8 ULA range, are supposed to be randomly defined. This is done to maximize the probability that any ULA prefix will indeed be\u00a0<em>unique<\/em>, not only within the site where the prefix is assigned but also truly globally unique across the entire Internet.<\/p>\n<p>The benefit of such randomness is almost no possibility of overlapping address space when different company\u2019s networks merge. All of the complex and potentially difficult renumbering, NAT configurations, or network overlays IT network administrators have had to rely on when dealing with overlapping IPv4 private address ranges goes away when using properly randomly-generated ULAs.<\/p>\n<p><strong>3 Ways to Ruin Your Network with IPv6 ULAs<\/strong><\/p>\n<p>For guidance and best practices on deploying IPv6 effectively, consider consulting an <a href=\"https:\/\/www.infoblox.com\/solutions\/ipv6-readiness\/ipv6-center-excellence\/\"><strong>IPv6 Center of Excellence<\/strong><\/a> to align your strategy with industry standards.<\/p>\n<p>Based on the characteristics of ULA we\u2019ve described so far there are three ways we can abuse ULAs that will, as typical with such abuse, save us time up front but cause much suffering down the road.<\/p>\n<p><strong>First: Deploy ULAs and NAT66<\/strong><\/p>\n<p>Have you heard the story of the grandparent teaching their grandchild to cook a fish?<\/p>\n<p>\u201cFirst, we have to cut off the head and tail before placing it in the pan.\u201d<\/p>\n<p>\u201cBut why?\u201d asks the grandchild noticing that the saucepan is big enough to hold the fish with its head and tail attached.<\/p>\n<p>\u201cWell, I\u2019m not sure exactly. We\u2019ve always done it this way.\u201d<\/p>\n<p>Turns out a distant ancestor didn\u2019t have a big enough pan and cut off the head and tail out of necessity \u2013 a step no longer necessary but taken out of habit.<\/p>\n<p>IPv4 private addressing and NAT, then, is the too-small-saucepan.<\/p>\n<p>First we used IPv4 private addressing because we worried we would not have enough addresses for enterprise networks. NAT provided the means for this but was always an inelegant and brittle kludge that broke or bent protocol behavior and interfered with application performance and reliability. Still, over time, the IT network folks began to perceive a measure of security from the way NAT hides the internal addresses of hosts on the corporate LAN. No help was the fact that the firewalls providing NAT were also providing a more concrete form of perimeter-based network security in the form of stateful packet inspection. It\u2019s been repeatedly demonstrated over time that perimeter-based security by itself is insufficient to protect corporate LAN and enterprise IT hosts and servers.<\/p>\n<p>Just as it sounds NAT66 typically provides stateful address translation between two IPv6 address prefixes \u2013 often ULA to GUA and back again. You still need all the NAT helpers and application fixups to make this configuration work with IPv6 and the resulting performance and reliability is just as brittle as with IPv4 NAT (it\u2019s even possible that said performance and reliability could be worse with NAT66 due to the relative lack of the opportunity to test at scale).<\/p>\n<p>Meanwhile, IPv6 was designed to allow for the configuration of multiple addresses on a host interface. Different address scopes allow for more granular administration of network routing and security policy. ULA addresses were not defined with the idea that they would be translated to Global Unicast Addresses at the enterprise edge. Instead, ULA addresses can be configured on a host interface along with GUA and link-local addresses, with each address routed and secured according to its proper scope: link-local on the local link, ULA addresses within a site (or between sites but not routed on the public Internet), and GUA addresses for Internet traffic.<\/p>\n<p><strong>NPTv6<\/strong><\/p>\n<p>By comparison, NPTv6 offers a way of statelessly translating between ULA and GUA prefixes of the same size (Figure 2). Since NPTv6 is stateless, no port translation is required nor other manipulation of transport characteristics. Other benefits include end-to-end reachability along with 1:1 address mapping, potentially allowing for redundant paths with no active failover required. Finally, no assumption about security is made given that a 1:1 internal-to-external (and back) mapping exists and no state is maintained with NPTv6.<\/p>\n<p>Perhaps most usefully of all, NPTv6 allows the effective use of ULAs to prevent the requirement of network renumbering without the accompanying brittleness of NAT66. One external network (GUA) prefix can be trivially replaced with another while the internal network (ULA) prefix remains the same.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-2906\" src=\"https:\/\/live-infoblox-blog.pantheonsite.io\/wp-content\/uploads\/simple-nptv6-translator.png\" alt=\"Figure 2. \u201cA Simple [NPTv6] Translator\u201d (courtesy of IETF RFC 6296)\" width=\"491\" height=\"471\" srcset=\"https:\/\/www.infoblox.com\/blog\/wp-content\/uploads\/simple-nptv6-translator.png 491w, https:\/\/www.infoblox.com\/blog\/wp-content\/uploads\/simple-nptv6-translator-300x288.png 300w\" sizes=\"auto, (max-width: 491px) 100vw, 491px\" \/><\/p>\n<p><em>Figure 2. \u201cA Simple [NPTv6] Translator\u201d (courtesy of IETF RFC 6296)<\/em><\/p>\n<p>Next time we\u2019ll look at the other 2 ways you can ruin your future network with ULAs as well as offer more suggestions for properly deploying them.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>To ULA or not to ULA. That is the question: Whether \u2018tis nobler in the mind to suffer the slings and arrows of multiple NATs&#8230; Ok, ok. I\u2019ll stop now (and in a moment, explain my lame joke to the uninitiated.) But first, in case you\u2019re wondering what exactly I\u2019ll be covering in this blog [&hellip;]<\/p>\n","protected":false},"author":319,"featured_media":2788,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"inline_featured_image":false,"_genesis_hide_title":false,"_genesis_hide_breadcrumbs":false,"_genesis_hide_singular_image":false,"_genesis_hide_footer_widgets":false,"_genesis_custom_body_class":"","_genesis_custom_post_class":"","_genesis_layout":"","footnotes":""},"categories":[17],"tags":[28,50,30,16,51,38],"class_list":{"0":"post-2905","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-ipv6-coe","8":"tag-ddi","9":"tag-dhcp","10":"tag-dns","11":"tag-infoblox","12":"tag-ipam","13":"tag-ipv6","14":"entry"},"acf":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO Premium plugin v27.3 (Yoast SEO v27.3) - https:\/\/yoast.com\/product\/yoast-seo-premium-wordpress\/ -->\n<title>3 Ways to Ruin Your Future Network with IPv6 Unique Local Addresses (Part 1 of 2)<\/title>\n<meta name=\"description\" content=\"IPv6 has a variety of uses and this article suggests how to best utilize them. Read more to find out how ULAs can be used through different demonstrations.\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.infoblox.com\/blog\/ipv6-coe\/3-ways-to-ruin-your-future-network-with-ipv6-unique-local\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"3 Ways to Ruin Your Future Network with IPv6 Unique Local Addresses (Part 1 of 2)\" \/>\n<meta property=\"og:description\" content=\"IPv6 has a variety of uses and this article suggests how to best utilize them. 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