4.3bsd UDP generates ICMP_UNREACH_PORT for broadcast packets

[Van Jacobson]

Description:
	UDP will generated ICMP_UNREACH_PORT in response to packets
	sent to the 4.2bsd broadcast address (host part zero).  On
	mixed 4.2/4.3 ethernets this can generate unnecessary traffic
	in response to Sun RPC packets or 4.2 rwho packets.
Repeat-By:
	Run rwhod on a 4.2 system.  Don't run rwhod on a 4.3 system.
	Monitor the network & observe one ICMP_UNREACH_PORT is sent
	by the 4.3 system in response to each 4.2 rwho packet.
Fix:
	A check could be added in routine in_broadcast for the
	4.2 broadcast addresses.  This helps both UDP and the two
	broadcast checks in tcp_input.  The diffs for netinet/in.c
	follow.  However, the unreachable port message seems
	questionable.  My ethernet if very busy.  If someone is
	using up bandwidth babbling to an unused port, why should
	I compound the sin by telling him he's a fool?  If he were
	smart enough to shut up on the unreachable, he'd be smart enough
	not to cause the original problem.  So, I also ifdef'd out
	the unreachable message in udp_usrreq.c & just increment
	a counter noting that a packet for an unused port has been
	discarded (diffs obvious & not attached).
	------------
*** /sys/netinet/in.c	Thu Jun  5 00:25:19 1986
--- in.c	Fri Nov 14 03:32:45 1986
***************
*** 421,429 ****
  	 * with a broadcast address.
  	 */
  	for (ia = in_ifaddr; ia; ia = ia->ia_next)
! 	    if (((struct sockaddr_in *)&ia->ia_broadaddr)->sin_addr.s_addr ==
! 		in.s_addr && (ia->ia_ifp->if_flags & IFF_BROADCAST))
  		     return (1);
  	return (0);
  }
  #endif
--- 421,441 ----
  	 * with a broadcast address.
  	 */
  	for (ia = in_ifaddr; ia; ia = ia->ia_next)
! 	    if ((ia->ia_ifp->if_flags & IFF_BROADCAST) && (
! 	        ((struct sockaddr_in *)&ia->ia_broadaddr)->sin_addr.s_addr ==
! 		in.s_addr
! #ifdef COMPAT_42
! 		|| ntohl(in.s_addr) == ia->ia_subnet
! 		|| ntohl(in.s_addr) == ia->ia_net
! #endif COMPAT_42
! 		))
  		     return (1);
+ #ifdef COMPAT_42
+ 	if (in.s_addr == (u_long)INADDR_BROADCAST || in.s_addr == INADDR_ANY)
+ #else 
+ 	if (in.s_addr == (u_long)INADDR_BROADCAST)
+ #endif COMPAT_42
+ 		return (1);
  	return (0);
  }
  #endif