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Date:      Fri, 03 Aug 2001 12:35:54 -0300
From:      "Daniel C. Sobral" <daniel.sobral@tcoip.com.br>
To:        "Rodney W. Grimes" <freebsd@gndrsh.dnsmgr.net>
Cc:        stable@FreeBSD.ORG
Subject:   Re: Request for testers: multicast patch
Message-ID:  <3B6AC4DA.30007@tcoip.com.br>
References:  <200108031516.IAA51292@gndrsh.dnsmgr.net>

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Rodney W. Grimes wrote:

>>[Bcc'ed to -net]
>>
>>On http://people.freebsd.org/~dcs/ip_output.c there is a port to stable 
>>of the revisions 1.127 through 1.130 of /sys/netinet/ip_output.c. These 
>>patches do the following:
>>
>>1) Enable one to send multicast packets without a default route or 
>>routes to the multicast addresses.
>>
> 
> This might break part of the multicast propogation protection,  IIRC
> this was a specific feature of the original Deering multicast code
> to prevent unwanted propogation of multicast packets on multihomed
> hosts.


Not doing this would break the RFC on multicasting. It says there that 
the app specifies the interface on which it will send the multicast packet.

And, specifically, if you have a default route, the application will 
send the packet on whatever interface it choses. If you have a route for 
the multicast address, even to loopback, it will send the packet on 
whatever interface it choses. The difference here is that we do not 
require that a route which will be ignored exists.

Note that this does not result in an application sending packets on 
multiple interfaces unintentionally, nor the absence of this patch 
prevents such applications from doing it intentionally.


>>2) Enable one to send multicast packets on an interface without an address.
>>
>>3) Prevent trouble if packets are sent through an interface without an 
>>address (vlan excluded).
> 
> What source IP address is used for 2 and 3???


For 2 it uses 0.0.0.0 (as per Bill Fenner's orientation in message to Ruslan).


Point 3 is not really related to IP addresses. Rather, it just avoids 
assuming that IA is non-null.

-- 
Daniel C. Sobral                   (8-DCS)
Daniel.Sobral@tcoip.com.br
dcs@newsguy.com
dcs@freebsd.org
capo@notorious.bsdconspiracy.net

Exhilaration is that feeling you get just after a great idea hits you,
and just before you realize what is wrong with it.


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