Re: transmech editorial comments

[Pekka Savola <pekkas@netcore.fi>]

On Fri, 14 Nov 2003, Erik Nordmark wrote:
> > ==> this seems a bit unclear forwarding for the case where the tunnel is not
> > used for forwarding when the hop limit is not decremented.  I tried to think
> > of a better rewording, but perhaps the easiest fix would be to remove:
> > 
> > That is, the
> >    IPv6 hop limit is decremented by 1 when an IPv6 packet traverses the
> >    tunnel.
> 
> How about replacing it with?
> 	That is, forwarding
> 	packets into a tunnel or packets received on a tunnel has the same
> 	impact on the IPv6 hop limit as for other interfaces.

This would be good independently, but the big picture is:

  IPv6-over-IPv4 tunnels are modeled as "single-hop".  That is, the
   IPv6 hop limit is decremented by 1 when an IPv6 packet traverses the
   tunnel.  The single-hop model serves to hide the existence of a
   tunnel.  The tunnel is opaque to users of the network, and is not
   detectable by network diagnostic tools such as traceroute.

   The single-hop model is implemented by having the encapsulators and
   decapsulators process the IPv6 hop limit field as they would if they
   were forwarding a packet on to any other datalink.  That is, they
   decrement the hop limit by 1 when forwarding an IPv6 packet.  (The
   originating node and final destination do not decrement the hop  
   limit.)

... wouldn't we just be repeating the second paragraph in a bit shorter 
fashion?

Btw, maybe one should reword "implemented", because that isn't really 
"implementation-specific", to avoid that connotation.  Maybe use 
"achieved" ?

> >    Implementations MAY provide a mechanism, for example IP Tunnel MIB
> >    [RFC2667], to allow the administrator to configure the IPv4 TTL.
> > 
> >                 [RFC3168] for issues relating to the ToS byte and  
> > 
> > ==> s/ToS/Type of Service/ (I wonder if we should call the field DSCP...)
> 
> DSCP is 6 bits out of the byte AFAIK, so keeping Type-of-service makes sense
> to me.

OK

-- 
Pekka Savola                 "You each name yourselves king, yet the
Netcore Oy                    kingdom bleeds."
Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings