Subject: (ngtrans) RE: v6[v4] address in ngtrans-bgp-tunnel

From: "Dave Thaler" <[email-masked]>
Date: Wed, 22 Aug 2001 10:51:24 -0700

Francois Le Faucheur writes:
> Would you agree "IPv4-mapped" definition matches exactly what we need?

I think the question really comes down to the tunneling aspect
of this draft.  It seems to say that multiple types of tunnelling
can be done, and proposes that a single address format be used
regardless of the type.  

*IF* that is a good idea (and I'm not saying that it is), then
I agree v4-mapped addresses are sufficient since they're not
used as the source or destination address in any IPv6 packet.
Other addresses are, and you may not know the peer's IPv6
address.  For this reason, I'm not convinced it's a good idea
to keep the address format separate from the tunnelling method.
For example, the list of tunnelling methods in section 6 should
probably include ISATAP as well.  If you're using ISATAP as
the tunnelling method, then it makes more sense to use the
ISATAP address as the nexthop in the BGP messages, rather than
the v4-mapped address.  (For one thing, it makes it easier to
manage since you avoid confusing the 2 addresses, and for 
another thing, you can easily detect misconfigurations where
two peers are configured to use different tunnelling methods.)

To reiterate one point of my earlier email, since I've seen
others restating the myth that (excerpt from Appendix A):
"Using ISATAP addresses would require an additional /64 prefix per
island (the latest ISATAP draft states that one has to use a
different /64 prefix for ISATAP addresses and native v6 addresses)."

This is NOT TRUE.  For the purposes used by this draft, there
is no need to assign a routable subnet prefix to the ISATAP link.
fe80::/64 is perfectly fine.

Furthermore, I question whether multiple tunneling methods are
really needed.  E.g., why would one want to do IPv6 over GRE/IPv4,
rather than ISATAP tunneling?  I think the draft needs to motivate
why multiple ones are needed, if it is going to allow a choice.

-Dave