[comp.sys.hp] Inquiry about broadcasting an address on a HP9000/320

anh@mit-amt.MEDIA.MIT.EDU (Viet Anh Ho) (11/23/89)

Two of our HP9000/320s think that they broadcast the addresses 18.85.255.255,
when instead, according to the outside world they are actually 18.0.0.0!

  # /etc/ifconfig lan0 
  lan0: flags=64b<UP,BROADCAST,ROUTE,RUNNING,IEEE,ETHER>
  inet 18.85.0.30 netmask ffff0000 broadcast 18.85.255.255

We couldn't find any reference on how to re-set their broadcasting addresses.
The following command won't do the job:

  # /etc/ifconfig lan0 $NODENAME netmask 255.255.0.0 up

We appreciate any suggestion and reference to the problem.

Thanks.

-anh (anh@media-lab.media.mit.edu)
-- 
Viet Anh @ The MIT Media Lab
E15-353, 253-0302

dfc@hpindda.HP.COM (Don Coolidge) (11/30/89)

If you're asking if HP-UX provides a way to arbitrarily configure your
interface IP broadcast address (a la 4.3BSD), the answer is, "not yet".
That capability will be available as a patch to the 7.0 HP-UX release,
and will be an integral part of all subsequent releases. 

The interface broadcast address is currently defaulted to all ones (4.3-ish,
and conforming to the Internet Hosts Requirements Document), subject to the
interface netmask and IP address. In your case (netmask 255.255.0.0; IP address
18.85.0.30), that would result in 18.85.255.255 (as in your example).

If other nodes on the LAN are seeing something else, you have a problem
that I don't understand and that should never be able to happen. If that's 
the case, please contact me via email at :

	dfc@hpindaw.hp.com

There's only one way I can conceive of that other nodes on your LAN could
be seeing 18.0.0.0 - if you have an application using sendto() with 18.0.0.0
specified as the target IP address.

By the way, even though the interface broadcast address is defaulted to all
ones, HP-UX will also recognize inbound and outbound datagrams with all zeroes
as valid broadcast packets.


- Don Coolidge

dfc@hpindda.HP.COM (Don Coolidge) (12/02/89)

>There's only one way I can conceive of that other nodes on your LAN could
>be seeing 18.0.0.0 - if you have an application using sendto() with 18.0.0.0
>specified as the target IP address.

>By the way, even though the interface broadcast address is defaulted to all
>ones, HP-UX will also recognize inbound and outbound datagrams with all zeroes
>as valid broadcast packets.

I've received some private email describing the problem in greater detail,
and wanted to post the final answer. The problem is rwhod, which is using
sendto() as I described above. HP's released networking code is based on 
4.2BSD, which used zeroes as a broadcast address. We've made many 4.3-ish
upgrades, but rwhod has not yet been one of them. Unforunately, the address
used by rwhod's sendto() is hard-coded in 4.2-ish zeroes.

So, for the systems mentioned in the original posting (6.0, 6.2), rwhod will
continue to pump zero-based packets onto the net unless you invoke it with
the -r flag (receive data only; don't send any). 

Administrators of large LANs might want to keep rwhod generally inactive,
anyway (on all machines, not only on HP systems) - large numbers of broadcasts
(one/node/3 minutes) unnecessarily eat up a lot of LAN and machine bandwidth
on LANs with lots of nodes.

- Don Coolidge

burzio@mmlai.UUCP (Tony Burzio) (12/05/89)

In article <4310077@hpindda.HP.COM>, dfc@hpindda.HP.COM (Don Coolidge) writes:
> Administrators of large LANs might want to keep rwhod generally inactive,
> anyway (on all machines, not only on HP systems) - large numbers of broadcasts
> (one/node/3 minutes) unnecessarily eat up a lot of LAN and machine bandwidth
> on LANs with lots of nodes.

You haven't seen network overload until you coexist with a VMS/VAX cluster!
The poor things constantly chatter amongst themselves.  For a short time
the VAXen herd were down today, and BOY did my HP-UX cluster speed up! :-)

*********************************************************************
Tony Burzio               * Oh no!  Not again!
Martin Marietta Labs      *         - the flower
mmlai!burzio@uunet.uu.net *
*********************************************************************