Saturday, May 8, 2010

link-local address, autoconfiguration IP address

Three addies for each device:

localhost address = ::1 (to talk to itself)
link-local address = fe80::/10 (to talk to other devices in the lan), even they are not connected to the net
world routable adddress = talk to the outside

"IPv4 addresses in the range are assigned automatically by a host operating system when no other IP addressing assignment is available, e.g., from a DHCP server. In IPv6, link-local addresses are required and are automatically chosen with the fe80::/10 prefix."

RFC 3927

When you plug in your laptop to, say, a comcast cable modem. You see "limited or no network connectivity". When you do ipconfig, you see an IP addy like this:

Autoconfiguration IP address:
Subnet mask:

How and when XP assigns it.

From M$:

Example 1: No Previous IP Address and no DHCP Server

Example 2: Previous IP Address and no DHCP Server

Example 3: Lease Expires and no DHCP Server

How to disable it on Xp:

For Windows 2000, Windows XP, and Windows Server 2003, APIPA can be disabled by adding the "IPAutoconfigurationEnabled" DWORD registry entry with a value of 0x0 to the following registry key:


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