Subject: Re: (IPng 5892) Re: Last Call: Internet Protocol, Version 6

From: [email-masked]
Date: Fri, 19 Jun 1998 12:54:20 EDT

In a message dated 6/19/98 11:38:45 AM Eastern Daylight Time,
[email-masked] writes:

> At 8:16 AM -0700 6/19/98, [email-masked] wrote:
>  > Is providing IP header length information necessarily meaningful
>  > at this point?  Suppose the destination is group or multicast.
>  > The packet may be transmitted on multiple interfaces with
>  > different amounts of header information transmitted on
>  > each interface.

>  A source of an IP multicast packet transmits that packet on one interface
>  only; it is the routers' responsibility to forward the packet to all
>  necessary links.  When a router originates a multicast packet, the same
>  model applies, in that logically the packet is "originated" on one
>  interface and then "forwarded" to any other interfaces required.
>  Forwarders are not permitted to insert headers into IPv6 packets.
>  (If they wish to add information to a packet, they can do so by
>  encapsulation.)

Telford Tools' <A HREF="http://members.aol.com/Telford001/#PACKET_SWITCHING">
VLAN Router</A>  contains a standard Berkeley network and 
socket layer.  Whether it runs as a host (pure LAN switching mode) or
as a router (VLAN routing moder), packet transmission takes 
place the same way.  The source address is filled in and
the destination is looked up in the routing table, and
the packet is forwarded out the appropriate interface(s)
with the appropriate IP headers. The VLAN router supports
several multicast receive interfaces, but the existence
of such interfaces are independent of multicast transmit and
these receive interfaces have no associated transmit logic.

In any case with IPv4, it would not necessarily make
sense to choose the same SERVICE TYPE on
all outgoing interfaces and there would be no obvious
reason to choose SERVICE TYPE on the basis
of the source address that happens to be chosen.

IPv4 options are not obviously outgoing interface
specific but there is no reason options should
not be outgoing interface specific in the future.

The point is the following.  In a router there
are multiple interfaces.  I think the claim is
that one interface is the source that should
govern that nature of the IPv6 header and
the packet is then forwarded to all other
interfaces that are not permitted to insert
headers into IPv6 packets.

In point of fact, in Berkeley and VLAN
Router architecture, a source address
is selected, but the packet does
not actually go through the output
logic associated with the transmit
interface associated with the receive
interface associated with that IP
address, and there is no obvious
reason why that output interface should
define the IP header for the packet
on the interface(s) from which the
packet is being transmitted.

Joachim Carlo Santos Martillo Ajami
<A HREF="http://members.aol.com/Telford001/">Telford Tools, Inc.</A>