![]() For example, imagine the scenario of a computer with two NICs, each with a link-local address on different networks. The scope ID indicates which scope the address is for. You can also tell it is link-local because the address begins with fe80.Ĭlear, simply-understood information on this topic seems to be rare, so I'm putting the rest of this together based on my best understanding of RFC 4007 and the other information out there.Ī computer can have multiple link-local addresses, each with a different scope. The article indicates that the presence of a scope ID in your address means it is a link-local address. Microsoft has published this article describing IPv6 addressing, which is the least-confusing article I found. This is an address that identifies the local interface, similar to 127.0.0.1. ![]() These addresses don't get routed around on the public Internet because they're not globally unique. It is an address that a computer assigns itself in order to facilitate local communications. It is available to use on the public Internet. This is an IPv6 address given to you by your ISP. IPv6 defines at least three reachability scopes for addresses: The number after the '%' is the scope ID. Oh, and all these three network adapters were link local. IPAddress has a constructor that accepts the address AND a scope ID. The answer was provided by Stephen: The number is the scope ID. What still confused me was why would the IPAddress class allow you to create an IP address in that format unless it was valid. As per MSDN, it uniquely identifies each network adapter and this property was introduced in Vista. I checked all the properties available for a network adapter using WMI and found that the numbers are exactly the same as the InterfaceIndex property of each network adapter. The addresses were: fe80::3dd0:7f8e:57b7:34d5%19Ĭlearly, the numbers after % are not some hex representation. I installed VMware to see what IPv6 address it issued. I just made some more observations about this and they match pretty well with what Stephen Jennings said in his answer. However, if I query the same using WMI, I get the address as fe80::71a3:2b00:ddd3:753f, without the %16.ĭoes the %16 have any special significance? I have a VirtualBox adapter which has both an IPv4 and IPv6 address. NET Framework classes to get the IP addresses for my machine: Dns.GetHostAddresses(Dns.GetHostName()) The result is that all protocols will see packet loss because the Ethernet frames were delivered to the wrong device, regardless of what IP address they use.I am using the. Modern Ethernet isn't a broadcast network – instead, Ethernet switches and bridges keep track of which MAC addresses were seen on which physical ports, and the switch will send the Ethernet frames through only one port at a time (the one where the address was seen last). IPv6 implementations using RFC 7217 use unique seeds when generating the interface ID, so collisions will usually not happen at all.īut aside from IPv6, the actual layer-2 network will be very confused by duplicate MAC addresses. Note that IPv6 has been phasing out the usage of EUI-64 for address generation for a long time, in favor of RFC 7217 "opaque" interface identifiers. ![]() same Ethernet) have identical MAC addresses, hosts generating their IPv6 addresses from EUI-64 will detect collisions during Duplicate Address Detection (which is mandatory in IPv6) and will mark the address as unusable. For example, thousands of hosts have manually configured addresses ending with the same :0:0:0:1. Regular IP routing is done on the entire 128-bit address, not just on the interface identifier, so machines on different networks can perfectly well use the same interface ID. they don't contact each other on layer-2), this is not an issue. If the interfaces belong to different links (i.e.
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