NetworkManager: IP address == Broadcast address?

[Chris Snook]

Rick Stevens wrote:
> Patrick wrote:
>> Hi,
>>
>> Problem: Internet via a Nokia from a laptop with F10 x86_64 does not 
>> (no longer?) work. Assigned IP address on laptop is the same as the 
>> broadcast address.
>>
>> A laptop with up-to-date Fedora 10 x86_64, NetworkManager version 
>> 0.7.0-0.12.svn4326, a Nokia E71 and a USB cable for use between the 
>> Nokia and the laptop. The Nokia has a working permanent GPRS Internet 
>> connection. Steps I do to setup a link between the laptop and Nokia:
>>
>> 1) I added the T-Mobile mobile broadband profile in NetworkManager
>> 2) I plug the USB cable into the phone and laptop and select "PC Suite"
>>    on the phone when asked
>> 3) I select the T-Mobile profile in NetworkManager
>> 4) NM starts chewing and reports after a few secs that a connection has
>>    been setup
>>
>> Result:
>> Internet no longer works on the Nokia nor from the laptop via the 
>> Nokia. In NetworkManager I select "Connection Information" and notice 
>> that the IP address and Broadcast address are the same. Pings fail 
>> except to the public IP address assigned to the laptop.
>>
>> Question:
>> Is this a bug? I'm no IP addressing expert so IP address == broadcast 
>> address might be valid.
> 
> It is absolutely incorrect.  Your NIC should NOT have the broadcast
> address as its IP address.

Not so.  PPP doesn't have subnets the way ethernet does, so broadcast is 
meaningless in this context.  Your netmask should always be 255.255.255.255 for 
a PPP connection, so the only address that could possibly be calculated for a 
broadcast address is your own IP address.

The only bug is that NetworkManager is showing a broadcast address at all for a 
PPP connection.  It should probably not do that, to avoid exactly this sort of 
confusion.

-- Chris