IP address woes

Angelo Fraietta afraiett at bigpond.net.au
Thu May 20 08:37:48 UTC 2004

Chris Johns wrote:

> Angelo Fraietta wrote:
>> You are right in that it is not in the arp cache - I tested with arp 
>> - a , and the RTEMS machine was definately not there on the list - 
>> even though it responded back directly. Is there a way to set it  to 
>> load it to the cache when it receives a message?
> I assume the 'arp -a' command was run on MacOS. If so it would seem 
> interesting to have this happen as the Steven's book is based on a BSD 
> stack and so is MacOS X and RTEMS. I assume this is MacOS X.

yes it is

> There are ways to directly play with the ARP cache but I would not 
> recommend this approach.
>> Also, when the RTEMS is unable to respond to the broadcast from the 
>> mac, it is able to respond to a broadcast from the Windows machine.
> What do mean by cannot respond ?

RTEMS says
Couldn't send out socket - host is down

>> Why is that the case? When this occurs, I unplug and replug my mac 
>> back in, and RTEMS can now find it - but the mac still can't find the 
> Not sure. Maybe the Mac's ARP cache is being flushed when disconnected.

It is - but the enry wass not there in the first place. Mayby it 
remembers that it could not find it?

> I would check the ARP cache entries against the tcpdump data.
>> How does a ping work? The machine pinging does not yet have the 
>> ethernet address before the ping?
> Ping is an ICMP echo command. ICMP sits next to IP and uses the same 
> ARP cache in the same manner as IP.
> What are the IP network configurations of each machine involved ?
>> I don't think that this is the case.
> You can prove this with all machines connected and tcpdump. It may be 
> a good to check this out.
> Also how are these machine connected, ie hub, switch etc ?
Tried on both a hub and a crossover cable

What would I do in RTEMS to do the tcpdump?

Angelo Fraietta

PO Box 859
Hamilton NSW 2303

Home Page


There are those who seek knowledge for the sake of knowledge - that is CURIOSITY
There are those who seek knowledge to be known by others - that is VANITY
There are those who seek knowledge in order to serve - that is LOVE
    Bernard of Clairvaux (1090 - 1153)

More information about the users mailing list