OT: Is the AutoIP range a special case IP address range?Bill Auerbach wrote:
  I just found out through testing that the PC with a NIC in the 192.168/16 
subnet (netmask 255.255.255.0) will ping and connect to devices on the physical 
network in the AutoIP range (169.254/16).  This is on a WinXP PC.  I find the 
ARP table contains AutoIP addresses and I can ping and open connections to the 
device at the AutoIP address.

  Is this something that is expected to occur?  Is it specific to Windows?  
I've not come across any RFC that mentions that this 'bridging' should or can 
occur.

Windows has simply set up two IP addresses on the same network interface, one 
AutoIP and the other in the 192.168.0/24 range. If you have a look at the 
network traffic with Wireshark you will find that pings to 169.254/16 are being 
sent from the PC using an IP address in that range. No "bridging" required. The 
AutoIP address might not appear in "ipconfig /all", so the only evidence will 
be if you try to send to an AutoIP address.

It might allocate an AutoIP address when the network interface goes active 
(before getting a DHCP address, or even if it has a static IP address 
configured), and keep it for later use, or it might allocate an AutoIP address 
when it needs to use one because it wants to send to an address in that range.

I'm pretty sure my Mac does the same but haven't tested it lately.


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