Subject: Re: Incorrect source address on multicast packets on multihomed m achines? (fwd)

From: Susanne Witschel <[email-masked]>
Date: Sat, 27 Jun 1998 13:19:09 +0200 (CES)

I forwarded the whole thread of messages to a colleague whos more familiar
with Suns than me. Here's his answer:

---------- Forwarded message ----------
Date: Fri, 26 Jun 1998 15:33:11 +0200
From: Olaf Erb <[email-masked]>
To: Susanne Witschel <[email-masked]>
Subject: Re: Incorrect source address on multicast packets on multihomed m achines?  (fwd)

     * You can't control which IP address outbound TCP connections come
       from on a box with more than one IP address. In the words of a Sun
       employee, "The current status of the 'problem' is that it was
       never guaranteed to work that way. The system now does pick one  
       address randomly." The work around is:
       "ndd -set ip_enable_group_ifs 0", and make sure that the interface
       address you want to be the primary address is ifconfig'ed last.

Gruss,
Olaf

-------------

 Susanne Witschel                      [email-masked]
 University of Karlsruhe
 Computing Center

---

From: Toerless Eckert <[email-masked]>
Date: Sat, 27 Jun 1998 18:50:32 +0200 (MET DST)

>        address you want to be the primary address is ifconfig'ed last.

I am not familier with current SunOS-5.6 bugs because i still use the good
ol' reliable SunOS-5.5.1, but some comments:

1. The behaviour of the "ip_enable_group_ifs" cannot considered to be a bug
   in the first place, rather it's a new feature. To cite "ip.c"
   (yes, i prefer citing documentation too, but i couldn't find it
    there ;-(:

   * ip_enable_group_ifs controls if logical interfaces should be
   * grouped together if they are on the same subnet.  By grouping
   * logical interfaces on the same subnet, the IP module can make an
   * attempt to balance traffic that leaves via a subnet across multiple
   * interfaces that are attached to it.  This allows a machine to
   * exploit switched Ethernet technology to allow 10n Mbit/sec, where n
   * is the number of physical taps on the Ethernet switch.
   *
   * If this variable is changed with NDD, the appropriate grouping/ungrouping
   * of interfaces will occur.

2. I would consider it to be a bug if it is not possible to specify a
   specific ip originator address for outgoing packets in case one does
   a bind(0 before the connect. I don't think that this is the case in
   SunOS-5.6 though.

3. From what i remember, ip_enable_group_ifs does not apply to the 
   problem we are discussing because the machine in question does only
   have different interfaces on different subnets, but not multiple
   interfaces on the same subnet.

Regards
	Toerless

P.S: For ip_enable_group_ifs=0, 105786-05 does fix some default handling.