Localhost - value fe80 :: 1% lo0
Addresses in the fe80 :: / 10 range are local-local addresses. Addresses are only important for the link they are on, so a device with multiple interfaces can have the same address, and of course, will have the same local local area network on all of its interfaces.
This is where the% sign comes into play. This is the interface identifier on the device, which will distinguish the interface on which the address resides. Different different operating systems will have different meanings after the% sign.
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We are looking at writing "fe80::1%lo0 localhost"
to a file /etc/hosts/
in OS X.
This means that the hostname "localhost" uses the local IPv6 address "fe80::1"
in the zone "lo0"
. Link-local means that this address is not routable and will be dropped by any router on the local network (at least they should).
As we talk about OS X, a typical OS X "lo0" iface configuration is:
lo0:
inet6 :: 1 prefixlen 128
inet 127.0.0.1 netmask 0xff000000
inet6 fe80 :: 1% lo0 prefixlen 64 scopeid 0x1
This shows that the main purpose of this link-local address is to maintain the loopback network link in the link-local address space. But there are several applications that use it.
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