Re: Router incompatibility with Vista

Graham J wrote:
[snip]

The other problem that seems to missed in this thread is the difference between routers and computers providing DHCP services. Computers build a table of leases and hold it as a file. This allows them to reload the data at start up and continue to issue the same address to the requesting device until such time that a "new" computer requests an address and there are none in the "unused" pool.

Routers do not have a mechanism (in general) to hold the information when powered off, so will start from a clean *** at power up (possibly after re-boot also). There is no reason to lose this information otherwise, as it is needed to prevent duplicate addresses being issued.

Most computers help the situation by assigning themselves the address they last had, if there is no DHCP server available. But this is only true when the computer can see a network connection, for example one provided by a separate switch. In a domestic situation the switch and DHCP server will be combined in a router, so if the router is switched off, the computer does not see any network and will assign itself the autoconfiguration address.

However, when the router is switched on the PC will recognise that there is now a network connection and request an IP address. I suspect this is not reliably true of W98 (or earlier) machines, but it seems to be true of W2k

I know XP checks when a network connection becomes active, but I'm not sure if it checks at intervals if it doesn't initially find a DHCP server. ISTR autoconfigure addresses being allocated by XP under these conditions.

and XP. Some routers can be configured to issue IP addresses by reference to the client's mac address - this is convenient when you want to maintain consistent addresses.


That's what I use, but only because the router doesn't have a DNS server (as opposed to a pass-through proxy) and I can use a common hosts file.

If you have a separate switch and router (perhaps because you need to connect more than 4 computers simultaneously) my first paragraph applies. Because the computer sees a network but might not see a DHCP server, it uses the address it last had. If the DHCP server (in the router) is then switched on, another PC might request an address. The DHCP server chooses an address according to its internal rule, but before it issues this address, it should check to see whether any computer already connected to the network has that address - if so, it tries another. Of course, some routers might not check!! (see definition of the word "should" earlier in this thread.


The problem with checking if an address is in use is that it relies on getting a response to a message to that address (eg a ping). Some firewalls may stop that response happening by default :-( (Yes, I have seen that situation.)

PeeGee
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