Which Range of Link-local Addresses Can Be Assigned to an Ipv6-enabled Interface?ã¢â‚¬â€¹
In a recent article, I wrote about some of the common questions that IPv6 novices sometimes ask. We and then asked the question, "What are the typical questions you get when educational activity an IPv6 form?" Frequently, IPv6 instructors field questions from their students about IPv6 link-local addresses and how they piece of work. This article builds upon theIPv6 newbie questions theme and covers a couple of the IPv6 addressing nuances that are often surprising to IPv6 neophytes (and sometimes IPv6 veterans, too!).
It is relatively easy to grasp the concept that unicast addresses are used for one-to-i communications. Public IPv4 addresses are familiar to most, so grasping IPv6's global unicast addresses (GUA) (2000::/iii) is straightforward. Regardless of whether your organization's public IPv4 or global IPv6 addresses are provided past an RIR or your upstream Internet access provider, they are gratis to exist used to source and receive Internet communications.
Most enterprise organizations utilise private IPv4 addresses (east.g., 192.168.0.0/sixteen, 172.xvi.0.0/12, or x.0.0.0/viii) for their internal networks. However, with IPv6, beginners find that FD00::/8 Unique Local Addresses (ULAs) exist for private network addressing, although their use is not generally recommended. You are encouraged to read RFC 4864, Local Network Protection for IPv6, to larn well-nigh why you practice non demand private addresses for your internal networks and why y'all later do not need NAT for IPv6. Please also read Tom Coffeen'due south eloquent blogs (part 1 and part 2) on "three Ways to Ruin Your Hereafter Network with IPv6 Unique Local Addresses". This is besides a topic that nosotros discuss in our IPv6 COE Podcast #3.
Many people are familiar with how multicast addresses are used for one-to-many communications. IPv4 multicast addresses (historically referred to as Course D addresses) are inside the 224.0.0.0/four range. IPv6 multicast addresses starting time with the two virtually-significant hex digits "FF" and take the format FF00::/8. Afterwards the "FF", the next 4 bits of the address represents the flag value, and the following iv bits of the accost is the scope of the range of the multicast message. IPv6 multicast addresses can be used for link-local LAN communications or they can exist scoped for site-specific communications or even global use. An IPv6 multicast address for well-known link-local letters would start with "FF02" and you may recognize that FF02::1 is the all-nodes link-local multicast group address.
Only IPv4 has broadcast every bit a method of sending ane packet to ALL nodes on the electric current LAN. Whether the package's destination accost is 255.255.255.255 and intended for all hosts in the unabridged circulate domain or a broadcast address express to a specific subnet (e.one thousand., 192.168.i.255), both are converted to an "all-ones" layer-2 MAC accost FF:FF:FF:FF:FF:FF. Broadcast packets are sent out all Ethernet switch ports, regardless of whether or not there are any hosts on the fastened segments that demand or want the broadcasted letters. On the other manus, IPv6 doesn't use the broadcast method of packet delivery and so there is no equivalent IPv6 address type. IPv6 networks will never use broadcasts on a LAN. Yet, sending an IPv6 packet to the all-nodes link-local multicast group accost (FF02::i) comes close to that functionality.
The concepts of unicast, multicast, and broadcast and their accompanying addresses are familiar to IPv4 experts. However, there is 1 less-popular address type that tin can be used for unicast communications on a confined LAN segment. The caveat with these addresses is that they are only locally-meaning (i.e., restricted to a single LAN broadcast domain) and are never used to source or receive communications across a layer-3 gateway.
When first learning about IPv6, students are ofttimes surprised by the fact that IPv6 has another address type that is much different from the IPv4 address types that they are already familiar with: the link-local accost. Typically, link-local IPv6 addresses have "FE80" as the hexadecimal representation of the showtime 10 bits of the 128-scrap IPv6 accost, and then the to the lowest degree-significant 64-$.25 of the accost are the Interface Identifier (IID). Depending on the IID algorithm the node'due south operating arrangement is using, the IID may use either modified EUI-64 with SLAAC, the privacy addressing method (RFC 4941), or the newly published Stable SLAAC IID method (RFC 8064).
When a host boots up, it automatically assigns an FE80::/ten IPv6 address to its interface. You lot tin can see the format of the link-local address below. It starts with FE80 and is followed by 54 bits of zeros. Lastly, the concluding 64-bits provide the unique Interface Identifier.
FE80:0000:0000:0000:abcd:abcd:abcd:abcd
If you want to learn more nearly link-local IPv6 addresses and their usage on a LAN, delight read the latest edition of Rick Graziani's book "IPv6 Fundamentals: A Straightforward Approach to Understanding IPv6".
Many people get dislocated most IPv6 link-local addresses when they are first learning about IPv6 because there isn't actually whatsoever IPv4 equivalent of this type of IPv6 accost. Withal, the only thing that comes close to IPv6 link-local addresses is the IPv4 Automatic Individual IP Addressing (APIPA) method. When a host fails to obtain an IPv4 address with DHCP, it resigns itself to its fate of being incommunicado, and assigns its interface an APIPA address. You lot accept surely witnessed (probable in a moment of exasperated troubleshooting!) a host with an IPv4 accost in the 169.254.0.0/xvi range (see RFC 3927). Like IPv6 link-local addresses, these APIPA addresses are usable addresses for unicast communications inside a single broadcast domain on the LAN.
Link-local IPv6 addresses are on every interface of every IPv6-enabled host and router. They are essential for LAN-based Neighbour Discovery communication. Later the host has gone through the Duplicate Address Detection (DAD) process ensuring that its link-local address (and associated IID) is unique on the LAN segment, it then gain to sending an ICMPv6 Router Solicitation (RS) bulletin sourced from that address.
Even routers use link-local addresses on each of their own interfaces. When the router receives the host's Router Solicitation (RS) message (sent in the attempt to find any router available on the link and to reach the rest of the network), the router immediately replies with an ICMPv6 Router Ad (RA) message. That RA message is also sourced from the router's ain link-local accost. When the host receives the RA bulletin, information technology reads the contents, follows the address configuration method indicated in the packet, and, in the case where SLAAC is the address configuration method, uses the RA-included IPv6 /64 prefix to configure a globally-scoped accost. The host will and so use the router's link-local accost (and MAC independent in the RA) as its default gateway.
At this point, that host would have used this router's link-local IPv6 address as the next-hop accost for the 0::/0 IPv6 default route. Subsequently inspecting the host's routing table, IPv6 greenhorns are frequently surprised to find that a link-local address is the next-hop address for that route. They so might exclaim "How tin that be?!" The retort is "Keep Calm and Learn Link-Local."
The link-local address might be understood as an address used as a kind of stand-in address – one that indicates the link that should be used to reach the side by side hop. The host will all the same send packets sourced from its own global accost and destined for the global accost of the target. Yet, the link-local address in the routing tabular array is used to map to the side by side-hop's MAC address in the neighbor cache. The link-local address is not used as a destination address of any of the host's off-net packets, but rather, is just a way for the host to acquire the MAC address of the adjacent-hop router that will forward the host'due south IPv6 packets onward to the destination address. The host just needs to get the bundle started on its hop-past-hop journey toward its destination (and getting the packet to the default gateway is the first step).
Fledgling IPv6 engineers might be initially alarmed by the fact that the router'south link-local address is a perfectly valid next-hop accost. But over fourth dimension, an agreement of the neighbor discovery enshroud solidifies and this configuration becomes an accepted norm. This fact is also reinforced when y'all observe the IPv6 unicast routing tabular array on whatever router, and yous immediately run into the link-local addresses of its next-hop routers. Routers do non modify the source or destination global unicast accost in the packets, but they do utilise the adjacent-hop link-local addresses every bit a mode to become the packet forwarded across a link onward to the packet's ultimate destination.
The other surprising fact that IPv6 rookies may discover is that the same link-local accost can exist used on a node's multiple interfaces. This is because, typically, each node'due south interface is presumably connected to a different "link." Therefore, the local-significance rule of the addresses means that, then long at the IID of the link-local address is unique on that segment, all is right with the world.
IPv6 nodes employ either EUI-64, privacy addressing, or stable-SLAAC to derive the IID (i.eastward., the last 64 bits) of the link-local accost. In either instance, the IID is not easy to remember and may require cutting and pasting if used in a static configuration. The same link-local IID dilemma exists for routers and other middle-boxes like firewalls and load-balancers. In these situations, we may need to statically configure the adjacent-hop IPv6 address for a static route or for the default gateway on a host. Therefore, we want a way to brand things easy on ourselves when information technology comes to the configuration we cull to use.
One method to make things easier is to manually assign the link-local accost to the upstream router's interfaces. If you assign the link-local address FE80::1 on each of its interfaces and if that link-local address is unique on each of those LAN segments, then this becomes the default gateway for the hosts on those LANs. Therefore, each host, no matter on which LAN, will meet FE80::one as the adjacent-hop IPv6 address for the default route in its routing table. The movie below illustrates this thought of using locally-administered link-local addresses. In the example of servers with statically assigned IPv6 addresses and default gateways, this can brand things simpler for the system administrator.
Link-local IPv6 addresses may be initially disruptive when y'all're first learning nearly IPv6. Merely you volition quickly become familiar with how they piece of work and appreciate their functionality. At starting time, information technology may seem foreign to use a link-local IPv6 address as a next-hop accost for a static road or equally a default gateway router in a host's routing tabular array. Nevertheless, there are methods such as locally-administered link-local addresses that can dramatically simplify this static configuration. It's just another way in which IPv6 can be simpler than the legacy IPv4 protocol.
Source: https://blogs.infoblox.com/ipv6-coe/fe80-1-is-a-perfectly-valid-ipv6-default-gateway-address/
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