RE: Win95 won't forget old IP address

[Munil Shah <[e-mail]>]

>
>We've just moved the client to a new subnet and attempted to boot.
>The sequence of events is:
>(1) Client sends REQUEST via all-1's broadcast
>(2) Router forwards to server via unicast
>(3) Server sends NAK to router via unicast
>(4) Router forwards to client via unicast

This seems wrong. Router should not be sending unicast NAK here
regardless of
whether bcast bit was set or not. As per RFC, if the bcast bit is not
set, unicasting
is done to the yiaddr. But in case of a NAK, yiaddr is 0 so unicasting
is not possible.
Router must broadcast NAK here. 

And again which address would you send bcast to? You cant use the NAK'd
address
because the server knows that's a bad address for whatever reason.

>(5) Client drops packet because it's not an all-1's broadcast

Are you sure about this. Have you taken sniff? 

>Conclusion?  The Win95 DHCP client is broken.
>
>Unfortunately, I can't prove the broadcast/unicast statements above,
>because
>the router broke sometime between 17:42:41 last night and this morning
>when
>I went back to try it again.  Sigh.  I probably won't be able to try
>again
>until tomorrow at the earliest.
>
>I see that RFC 1541 provides for the broadcast bit, which says that in
>step
>4 above, the router should use a broadcast rather than a unicast if the
>bit
>is set.  I cannot tell at the moment if the bit was set right now
>either;
>that too can be tested when I get the replacement router.
>
>In any case, we are somewhat confused about why we would need to do
>this.
>Using a broadcast address at both the link layer and the IP layer at
>this
>step seems very expensive and unnecessary...  Why can't we just use the
>client's MAC address at the link layer, regardless of what's at the IP
>layer?
>
>Our supposition si that the router is (was) indeed doing just this, but
>the Win95 DHCP client dropped the NAK packet because the broadcast
>address
>was not all-1's.  Does anyone else's experience back this up or refute
>it?
>
>If this is true, it may be impossible for us to support Windows 95 DHCP
>clients, until Microsoft fixes this.  This would be something of a
>disaster;
>people have been clamoring for support for Windows 95 DHCP clients, but
>it
>appears that without modifying either the Cisco code or the Microsoft
>code,
>it may be impossible.
>
>Several people have said that I need to be running Cisco IOS 9.21(4) or
>later, or 10.0(3) or later.  Anyone know if 11.1 qualifies as "later"?
>-- 
>Mark Sirota, Network Systems Engineer
>University of Pennsylvania, Information Systems and Computing
>[e-mail], 215/573-7214
>